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My other project(s).. post-war Sunbeam m/c's

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Ok.,  here's new topic, in the new public Social-Scene section of the TR Register forum..  This thread is in essence what's happening in my own garage, workshop or boat yard,  where I share my approach to and my work on various projects, which may be of passing interest to some of you.  If they are then please at least click on the 'like' so I know I'm not wasting my time., &/or join in the conversation with me.  It's not a one man blog - this is a forum which invites you to join in.   

For those who have access to all areas of the forum - I am also recording the process of buying a TR4A from the United States, and my restoring and then possibly also modifying it.  Again you are more than welcome to join in that conversation.

But for here and now, on a cold day in Suffolk,  in March '20 ..well here's a little of the progress on motorcycle engines I'm presently working on. .

I say engines in plural because I presently have three Sunbeams ;  Katie  is the 1948 'early' S7,  and then I have the sister bikes of 'Nudge' ..the skinny wheeled S8 (formerly my daily rider)  & 'Pudge' ..the fat tyred S7-deluxe.  Each were registered NXN from the same borough of London - Pudge on the day after the Coronation, and Nudge some  five weeks later. Both were finished in mono-chromatic silver and almost certainly were show bikes in that dealer's front window for that very special occasion. 


^ This is Pudge ..on the day I bought her.

However., at present neither of these bikes are presently on the road, and each engine is in bits.  Nudge's engine has the correct / original (# S8 116xx) for that frame,  but Pudge's engine  is # S8-31xx, which is incorrect and very likely from a late-1948 bike. (NB. from 1948 all the engines had an S8 prefix even when fitted to the S7-deluxe).  I do have a spare engine but that's from a slightly later bike (c.1954) so there's really no point in my using that ..as its number will still not match, and anyway that also needs rebuilding.


^ Pudge is the subject of a total restoration, and stripped to be repainted, but it stalled because I take on too many projects at once, often according to the season / weather.  This time of year, two years ago - I tried to jump start things by passing the engine over to a specialist to rebuild.  Our agreement was for a fixed price of labour + machining costs + any parts needed. Along with the engine I supplied many new parts such as seals and gaskets, timing chain, etc. and also a selection of good used parts which included x3 cylinder heads ..for the specialist to use whichever was the best one.  Unfortunately that specialist took advantage of me and the bill trebled, and still the engine was totally in bits.. So I took the work away from him - expecting to just have to reassemble it myself.  Naturally I looked at what had been done .. but the more I looked the more I became dismayed.  After a while I put the project away ..for fear that my pent-up frustration would explode and I'd smash it.  I moved onto another project and got on with that. This was two years ago.

I discarded the supposedly 'restored and ready to refit' cylinder head from Pudge, because its cooling fins had been butchered (..by a prior owner trying levering the cylinder head off) and the valves were not seating well. I substituted that with the best condition cylinder head I had on the shelf (..one of those I had supplied to the specialist) and reworked that.  However although the cylinder head numbers are not in accurate sequence to those on the engine block, nor are they recorded - their number is generally within five hundred of the engine block number.  And this one (#111xx) wasn't.  Nudge's original cylinder head ended up on Hovis, a 1955 S8 I sold last year,  whose engine I had borrowed to use in Nudge ..which at the time was my daily rider.  When the correct and original engine was refitted back into Hovis  I didn't bother to swap the head back, as I already had a good 'spare' cylinder head on my parts shelf, although the number on that number is just 30xx.

So I have the original engine block for Nudge, but whose cooling fins have also been butchered ..so I don't know whether I'll reuse that in a nice bike.  And I have Pudge's 1948 engine block (which is in nice condition) but whose rear dry-liner cylinder sleeve had been replaced, by said specialist ..but not sealed.!  I hope, I've now resolved that issue (that cylinder would have had no compression) by using Loctite VHT wicking bearing lock.  Only time will tell if that 'fix'  has been successful.   And then I have two cylinders heads, one from a 1953 bike and the other from a '48 bike.  The annoyance is that I had reworked the later head for the early engine block.!  This all comes down to my having done this two years ago when I used the best of what I had available at that time.  But now both engines are in bits - I've decided to put the later head with the later block and the early head on the early block.  I'm sure it makes no practical difference and these cylinder heads are supposed to be the same ..But I will know.  

Are there any differences ?  . . . yes,  but as far as I can tell those differences are superficial. 


^ the older (c.1948) cylinder head (top) in comparison with the c.1953 cylinder head (bottom). The difference seen is in the casting shape of where the head gasket sits.  On the older one the casting shape curves much closer around the studs. As the head gasket is exactly the same, it really makes no difference.  Another change is in the rear right-hand bolt hole (..next to the timing chain chimney). It's not clear to see from this angle but the height of the boss, which the stud bolts through, is 1-1/8"on the early head, but only 3/4" high on the later one.  Naturally stud length will have to be matched to those.

That seems a retrograde change as I have heard of these bosses cracking when over tightened. I might only imagine that it was a change to help in production, because in all otherwise important aspect such as porting, combustion chamber shape, spark plug position, etc,  all seem to be very similar. 

NB. Katie's / the 'early' S7 cylinder head was different to these in many respects. The spark plug position within the combustion chamber was for example different, as is the stud pattern, as is the camshaft and rockers. 

Anyways up.. I've made the decision to use the cylinder heads in close accordance with the engine blocks numbers.  So  ;  Pudge engine # S8-3178 will now have cylinder head # 3072  and  Nudge's engine # S8-11660 with cylinder head # 11107.   I'll not mix components within each block, nor within each cylinder head ..they'll all go back in where they came out.  But I have two engines to rebuild, so set about getting the parts ready.


^ the early # cylinder head as it was from sitting in store.  I had bought it together with a job lot of garage clearance bits, and done a drain-down test on this a couple of years ago ..so knew the valves needed re-grinding, but otherwise it appears to be a good condition item.   The original design of breather on these engines was stupid. It breathed out of the rocker cover and the fumes / mist / humidity was to the open air at the front of the engine. Of course this ran down the front face and was then blown back along the cooling fins, which being hot baked the oil residue on.!    One of the first mods many owners do is to buy a catch box from Stewart engineering (Sunbeam specialists) which a drain pipe fits to ..to take any mist down to under the engine. 


^ camshaft looks in serviceable condition.. I'll clean, inspect and measure that at some point to see if it still looks good. 


^ inside wasn't very clean.


parts cleaner and power wire brush made a good start, but as you can see cleaning up inbetween the cooling fins had limited success. 

I had to resort to chemical cleaner (acid) to improve this. . .


^ That's better.  I used what's known as 'de-carb'  short for de-carbon, which outside industrial use is sold as oven cleaner. And it literally dissolves carbon, which of course includes burnt on oils, but also is a viscous acid that dissolves carbon based things like skin, finger nails, hair, eyes, bone ..so  USE with GREAT CAUTION !

The de-carb also slowly attacks the aluminium, and leaves dull grey patches. After a good scrub down in water to get rid of most of the acid (I used a jet-wash, close up and at full power) the discolouration can be cleaned off with wire brush &/or scouring pads with engine cleaner.  It's perhaps not as pleasing a finish as bead-blasting - but for a single engine component it is much more convenient to diy it,  than to back n' forth to someone who has the facilities.  And after a few weeks on the road they'll not be much difference in the look of various engine parts. 

NB. that casting number seen in the rear corner is not on the later cylinder heads.    


Then I had something to work with, and could see what needed to be done.  I used a hand file to smooth out any dents and I used a Dremel to rework the combustion chambers.  . . 


^ the valves are so very close to the combustion chamber side walls, that even when open - the gas flow passed them has a very restricted route.  The job I'm doing here is to undercut the gasket face so the gasses have a greater width to get through.

The process takes great care and is a rather slow operation because of that,but otherwise is most likely very obvious ..so I'll cut to the chase . .


^ this shows a 2.5mm dia drill-bit, which I'm using as a width gauge to assess the amount of extra clearance the undercut is giving (with the valve open).  Before my re-work that drill bit didn't fit into the gap.  As you might see I've increased the width of the gas-flow route by 1.5 - 2mm. That may not seem a whole lot but as a 60-80% increase over the original gap of 2.5mm - it's significant ..and I've not touched the gasket face.  And as the advert says "every little bit helps".


^ likewise this photo shows a 5.5mm drill bit being used as a indicative gauge  ..which before I undercut the sides was a tight fit in that gap. So the clearance is now almost twice as wide as it was, and this runs about a quarter the way around the valve head perimeter. So again a significant improvement for the gas flow. 

The amount I've removed around the tight spot of each valve is similar, simply to aid the flow of gasses - both into and out of the combustion chamber.  Easier means less resistance, and hopefully more gasses moved in each fraction of a second. Inlet wise that equates to more fuel in the chamber so a subsequently slightly bigger bang.!  That's the basic theory ..although port and combustion chamber shapes, and the flow of gasses around the valve guides, the swirl effect within the cylinder, as well as valve timing and back pressures all complicate the exactness of the science.

Without changing the carburettor, simply getting the fuel mix through the cylinder head inlet port is the next thing I address. . .


The black line has been marked from the carburettor's insulator / gasket. The port into the cylinder head is a restriction, in this case by about 1mm all the way around but further in was also angled towards the rear cylinder.  That restriction might be likened to using a 21mm diameter carburettor in place of the standard 24mm one.  So the object here is to let the standard carburettor do its job, and then again to allow an unrestricted (but not larger) route for that fuel-mix into the combustion chamber.


The insulator block is standard, and the restriction within the casting is apparent despite the amount of aluminium I've already cut out.  Again I must emphasis that I am not changing to a larger carburettor, nor do I want the inlet tract to be any bigger than necessary ..because a greater cross sectional area would decreases speed of flow. All I'm doing here is getting rid of the restriction.


^ I simply use an appropriate size of penny-washer to gauge what I cut away. I'd like to think it's pretty accurate. 


^ once I was happy with the size and shape I polished the inlet port, to minimize surface turbulence.  However I don't bother to rework the exhaust ports on these engines because they are already massive (not at all restrictive) and any polishing would soon have a layer of soot over them anyway.

Subsequent to doing this I cleaned out rough lumps of casting within the fins, and cut away the timing chain tunnel where again a loose chain had worn groves in it, and generally tidied the casting up, redressed gasket faces, etc.

I then ground in the valves  . .


Ok so I cheat.. but time is time whether you're at work or whether you're retired.  I use the cordless drill on the valve stem and gently pull the spinning / grinding valve onto its seat.  Like doing it by hand - I use a touch n' go action rather than just spinning.   Again I used coarse and then fine grinding paste, and then just a little more with no paste at all. 

So finally..


With the valve's temporarily refitted, and the cylinder head put aside where it will not be disturbed, and leveled. each combustion chamber is filled with parts cleaner. Any fluid which leaks passed a valve will be seen in the ports.  If there' fluid in the inlet port then there's a possibility of either valve leaking but which fluid level goes down indicates where it came from. After 12 hours it ought to be obvious which need a little more regrinding.  On this cylinder I had to redo #1 cylinder's exhaust port. No problem and much better to find out now than after I had put the engine together and found it low on compression.  

So that's it for today.  Hope it's been of some interest and not too boring or long winded. 

Any questions or comments, do please - feel free to contribute.

Have a good weekend, Pete.

Edited by Bfg

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Great thread Pete, I just love the old post-war Brit bikes and always appreciate when enthusiasts spend time and skill (plus money) to restore them back to their former glory.

My era was the Jap bikes of the early 70's (including the Triumph T160 Trident) through to mid-80's. Here's my November 1970 CB750 K1, a 20,000 mile survivor which I'm slowly bring back to life having been off the road since 2015.  This weekend's job is to remove the four exhausts and deep clean all the nooks and crannies.

I'll look forward to the next Sunbeam instalment. 

Cheers, Andrew




Edited by Andrew Smith

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Wow Andrew  ..better than new condition.  Everything looks superb.  The Japanese bikes I had always seemed to have just so many nooks & crannies, most probably because they were the smaller models which favoured pressings for so many parts.  Darn easy to start and reliable though.  Roll on summer time eh.!   B)

Thanks for your support of this thread, and also thanks to whomever else click on 'like'.  I'll carry on then :)


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Really interesting to see your Sunbeam rebuild I shall look forward to the next installment.

Back in my motorcycle days (1960s) a friend had an S7 and I was impressed by the build quality and some of the design ideas used on Sunbeams


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Great thread Pete.

very interesting to see your rebuild and looking forward to your next episode.

Takes me a long way back to the days of tuning and racing Vespa's:ph34r: ( sorry chaps , am I still allowed to join in:lol: )

In mitigation I did have a Honda Bros for a short while but ear / balance problems have curtailed any two wheeled fun nowdays. 


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Hi Pete yes I like your thread I was into bikes as a16/17 year old but had a accident (not my fault) but in them days if you got hurt mothers did not like it, so bike had to go and she gave me money to get a car so I got into cars and banger racing. It was only a few years ago that considered getting a bike again but with all our other interests I did not happen. Loads of mates have bikes and still like to look at and listen about there stories, so keep you thread going it nice to know what other members get up to when not working on there TRs, 

Mike Redrose Group  

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Thanks Guys for your support..

OK a quick update and then I'm back out to the garage..

As said above - I'm working on the two engines from my 1953 Sunbeam S7-deluxe and S8 sister bikes, and that I'd just reworked (combustion chamber and a little porting) the older cylinder head, which is to go with Pudge.  Well over the last couple of days I've been playing catch up with the later cylinder head, essentially cleaning it up for reassembly.   In brief, this is what's what. 


^ although not in too filthy a state, particularly on the outside, there was still a lot of burnt-on / oil staining which while I rather-like not to have.  So I again used de-carb to scrub it out and then the power wash to blast it,  before more scrubbing with scouring pads and degreaser, and the rotary wire brushes on the cordless drill. The gasket faces were also cleaned and checked (..as I don't like a leaky engine).


I striped the rocker shaft and individually cleaned each component, and checked it for wear, any signs of damage, and for gunged-up oilways.  The rocker-arm forgings look pretty crude, and massively overweight by today's standards, but for a 1950's motorcycle which I'll not be entering in the TT - they'll do fine just as they are. 


^ although the rocker shaft and bushes were in surprising good condition and well within wear tolerance, I noted this rocker arm's bush was a little loose.  Worryingly, if these bushes turn in their arm - then the oil feed holes turn out of alignment ..and the oil feed directed to the cam lobe is prevented.  So although this was not turning, I took the precaution of pressing it out (using the vice and a suitably sized socket as a drift) then liberally covered it in Loctite and pushed it back in again.


The hole was very close but I checked each one anyway with the correct size drill bit - just to ensure that non are slightly misaligned or otherwise have a layer of crud in them.  The drill bit illustrates how the jet of oil from this drilling is directed at the camshaft.  NB. This 1944 (designed) motorcycle engine has alloy block, cylinder head & cases, and is indeed OHC. 


I had ground in the valves previously and again recently checked them (via a drain-down test over 48 hours) and their seating was good.  Subsequent to its disassembly and cleaning - I liberally oiled the pushrod tubes and reassembled the valves.   ^ here I'm just quickly running around with the die to ensure all the threads are clean and free running (cylinder head is on its side, but still I'm careful that no bits fall inside). 


I have a brand new camshaft and a good used one to fit into these engines.


^  visually one can see the new camshaft lobe is shaped for a longer open duration.  The inlet valve lifts are ~ 0.295"  and  0.311 for the old and new camshafts respectively.   It will be interesting to see if I can feel any seat-of-the-pants difference in performance.  I'll put the new camshaft into the heavier of the two bikes.


Again after checking the oil ways within the the camshaft are thoroughly cleaned out ..and likewise within the cylinder head (there are no external oil pipes with banjos on this engine, all the oil ways are internal) - the camshaft was liberally lubricated and refitted.   Pretty neat design layout don't you think.  

The pressurised oil route is from gear pump in the crankcase, up via a drilling to the camshaft's rear bearing, then through the camshaft itself to its front bearing. From there the oil is routed up through that fat stud (..front on the cylinder head / left) to the rocker shaft's pedestal (see below).  And then through the rocker-shaft to each rocker arm, lubricating each bearing in turn and pumping a squirt of oil over each cam lobe.  Thereafter gravity returns the oil to the wet sump via the timing-chain chimney at the back of the engine. This oil wash takes with it heat from the rear cylinder.    


^ an oil splash plate covers the camshaft, even within the rocker cover. 


^ Camshaft & rocker assembly reinstalled. I'll now go around and loosely assembly all the nuts n' washers to check they are all present and correct. 

So that's progress to date ..with this, the later cylinder-head now close to being ready to refit. Today I hope to do the same with the earlier cylinder head - so they'll be both to the same stage.    

Have a good weekend.   Pete.


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Yesterday, I was doing much the same with the earlier cylinder head (I'll be using in Pudge) as I had done previously (above).  Indeed most of the tasks were the same ..but I had a few other things to do with this one. . .


^ The rocker-arm shaft is hollow ..to feed engine oil under pressure to the rocker arms.  These arms are so drilled to intermittently squirt oil onto each camshaft lobe.  However, I noted that the holes in this shaft were particularly blocked up with crud/ hardened dry dirty oil.    I use a  2.5mm drill bit to clean them out and even then this drill is a loose fit ..so very likely they were originally drilled at 7/64" (2.78mm).  However these little holes* were clogged to such a degree that even a 2mm drill bit wouldn't push through by hand.  The area of a circle is  x r2  ..which means that each hole aperture should be 6mm2.   However, restricted as these were - the hole's cross sectional area was only 3.14mm2 .. so just a little over half its correct size. 

Naturally, if the camshaft is to be lubricated as intended / as designed - these holes do need to be cleaned out, and also the inside of the tube needs to be clear.  Access to inside the tube is via a screw plug in one end. Oddly that was not at all tight.  Not good because if oil leaks passed this - then oil pressure to lubricate the camshaft is less. If the screw were to fall out then there would be no oil to the camshaft at all and a sizeable screw floating around inside the engine to chew thing up.!  So after cleaning the shaft's inside gallery - I refitted its end plug with Loctite.

Btw.,  the scoring you see in the above photos looks very much worse than it feels or measures. The rocker arm bushes fit is within tolerance.


Next little job was the dowel which locates the timing chain sprocket in correct orientation to the camshaft . .


^ The timing chain sprocket loosely fitted - to show where the dowel locates into the end of the camshaft.  The following shows that sprocket off and its through-drilled dowel.


The problem with these is that they are through drilled ..so the dowel can get pushed out.  The shouldered bolt which fastens this sprocket is supposed to ensure it is secure, but still., once pushed through it becomes loose. A spot of weld on the back face fixes that.  Only a one minute job to do, but five minutes needed to get the welder out and then another five to put it away again !


^ cleaning the parts and ensuring the oil ways are clear is just part of the task, close inspection of every tiny part is needed. As you can see this tappet adjuster lock-nut is cracked in several places around its perimeter. (NB. This was face down against the rocker arm so the cracks were not visible without dismantling and cleaning).  In time this lock-nut would have split right through and possibly broken in two.. Would those lumps of steel have then been washed or vibrated into where the camshaft is spinning ! ? 

Next task was the rocker arm's contact pads. Being an overhead camshaft these bear directly on the camshaft lobes (ie., there are no cam followers). .


Rocker arms 1 - 4 (left to right).  The first two are as they were.  You can see coarse groves and the flat with hard edge from wear ..which at one time was smoothly curved.  The third one I'm in the process of regrinding, and the fourth has then also been smoothed down to 1000 grit.   These are not hardened faces, so I can regrind them by hand.  The first cut is with a power file directly across that lower hard edge.  The object is to restore a curved shape but to ensure the contact pad remains square (rather than introducing a twist in its surface) ..so care is needed (especially when using a hand-held power tool).  Thereafter I used sharpening oil-stones, laid flat on the bench as I worked the rocker's pad over it (coarse and then fine stones) to smoothly curve the surface plane and to cut away the wear ridges.  I then used the power file again to round either side (so there's no hard side corners to cut into the camshaft lobe) before working through grades of emery paper.  Thereafter the contact pad faces were polished (below).


^ looking as if those contact pad faces had been chromed 

Naturally they are not perfect ..but certainly are much better than they were, where their hard ridges would soon have worn into the camshaft lobes.



^ A number of studs needed to be removed and refitted. One needed to be replaced, and most needed their threads cleaning so the nuts would run all the way down the threads.  Mostly invisible - but the valve's guides, the camshaft and rocker arm parts were each liberally coated with engine oil throughout reassembly.  The one tappet adjuster lock-nut still needs replacing (others were all fine),  but otherwise this cylinder head is also close to being ready for refit. 

For the eagle eyed.. the safety pin is there as a reminder that the nut is deliberately loose.  The reason is that I'll take it off again (once the head is fitted onto the block) so that I can back-fill the oil way through the camshaft with engine oil.

That's it for yesterday's tasks..  so now it's time for me to do some more..

Catch you later,  Pete.    


Edited by Bfg

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yesterday afternoon I made the decision to try and clean Nudge's crankcase up to see if I might reuse it, and thereby retain the original engine number. . 


^ poor thing has been abused by some previous owner who "thought" they might prise off a tight cylinder head ..by locally levering their screwdriver against a cast aluminium cooling fin that's only 1/8" thick.!   Very likely the cylinder head was 'tight' because the inner stud's nut hadn't been undone (seen here inbetween the timing chain chimney and the rear cylinder). Admittedly it is not easily seen from the outside of the engine, even when the inspection cover is removed, so unless one looks at the manual - then its easy to miss.  


The engine was stripped perhaps six years ago because the head came off the top of a big end bolt.  I felt the vibration and investigated what the issue might be before it threw the rod ..so I was darn lucky that no damage was done.   At that time I was working long hours and so I simply used another engine in this, my commuter, bike.

So, to get on with things I spent quite a few hours simply cleaning up dents, chips and other signs of its hard life.  In fact this engine casting is about as bad as I've seen (and I have worked on a lot of these bikes).  I'm not talking about abuse here so much as the casting reflects a set of moulds which were at they end of their production life, or else this was cast on a Friday afternoon near close of shift.


This oil filler / dip stick tube doesn't reflect the evenness of sand casting that's normally a feature of these engines ..In fact it's just plain ugly. 


Around the drilled and tapped hole (for the chain tensioner) are other examples of defects cast into this case.  Above the clip is not a crack in the casting, its simply where the sand casting (mould) had started to crumble. 

I exaggerate not when I say - I spent over three hours going around this casting a little more presentable.  And while doing so - I was pondering on whether I should leave such casting faults as 'original' or to try and correct them.? 


^ Like the cylinder head.. the block's timing chain chimney had deep score marks from where its chain had been running very slack.  I can only imagine when listening this engine run ..the phrase "oh., they are all like that sir"  came to mind ! 

And then I acid cleaned the block (using de-carb) inside and out, and  jet washed it, and then scrubbed it again with scouring pads.


^ Still wet from being scrubbed.  On the face of it, after eight hours work, even I could barely tell the difference.!   Mind you., as I do things I tend to forget exactly what they were like beforehand.  The fins do look pretty straight now and the casting in general is perhaps a little more true the design. The acid matted the shiny surfaces and edges I had filed smoother and/or otherwise trued up.     

Some owners polish the flat areas inbetween the fins, which is not original ..but if the case is a good shape it can look very pretty.  Personally I prefer the finish of coarse grit blasting (not sand), so then it is an even mat finish all over.  But for a road bike this will do.


And then today I sought to address the broken cooling fins. . .


I don't have aluminium welding equipment and even though I bought high temperature gas blow-torch ..and low temperature aluminium rods - my prior attempts (on another engine) were less than 100% successful ..I guess because the whole darn thing is a heat sink and so I just couldn't get it up to temperature.  So here I'm attempting a simply cosmetic repair which involves Araldite and aluminium powder (saved after grinding the cylinder-head's combustion chambers). . .



^ aside from the colour difference.. with care it can be made to look half decent, but the reality when working with Araldite is that it's a very sticky yet floppy consistency. The aluminium powder helps but still it takes a bit of dancing around to get it in the right place just as it sets.



^ dusting over with aluminium power helps achieve the final  'cast finish' result.


I know of engines which have had bits of broken off fins stuck back on ..with Araldite,  but I've never tried this aluminium powder filler mix before.  Time will tell if the heat / expansion / contraction of the aluminium, or indeed and engine's vibration causes these repair to break off again.  If it does ..well not all is lost - I can always clean them up again., and then have the fins professionally welded. 

That's it for today. Just an hour of work done but possibly more of a noticeable result than all of yesterday's long day.

Best regards, Pete.

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My memory of aluminium 2 part filler adhesives/putty was that they were good for up to about 150 degrees c.

Things like Metalset or Alumfast putty.


Peter W

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Yes thanks  ..I subsequently learnt of this . . 


Araldite® EP 300 A/B Adhesive is an extrudable, two-component, room temperature curing epoxy adhesive designed for service temperatures up to 400°F (204°C). This product is suitable for bonding a wide variety of materials such as metals, composites and many other dissimilar substrates.

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I've mainly been doing other stuff this week so just a little to update..


^ A bachelor's home..  Mine has elements reminiscent of a production line.

The two  engine blocks of the engine's I'm rebuilding.  Both I've tidied up in regard to filing the cooling fins and around the edges to diminish the appearance of knocks and scrapes incurred over the past 67 years, as well as some pretty awful original casting blights on the later case.  The other / older one (to the right) was professional bead blasted, and will be used in Pudge ..the S7-deluxe Coronation window-display bike.  The original to Nudge block - is the one I chemically cleaned and then used a scouring pad and degreaser on, and then last weekend - cosmetically disguised its broken top fin.  Now there's not nearly the visual difference as it may appear here ..due to uneven lighting. 



^ what I'm doing here is sorting / checking I have the components for each engine, along with all the correct fastenings and gaskets etc.  It may seem obvious to keep all one bike's bits together, which on the whole has happened but these engines have been dismantled for quite a time now, and Pudge's was dismantled by someone else,  and subsequently each box has been rummaged through looking for bits from Hovis which I sold in April springtime last year.

The paper-type  Oil filter is not standard, but is another little conversion I like to do on my own Sunbeams.  I have to convert Nudge's engine yet so I'll come back and share details of that modification in a week or two.


^ Timing chains. The top of the three shown is a new one which illustrates how little it flexes sideways (no wear in its pins or links).  The middle one is just slightly worn, and the bottom one is plainly just worn out.  

So there you go, as I say not a lot to report on this week, but enough "little steps at time"  in the right direct ..and progress will finally be made. 

Wishing each and all of you a good weekend,


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Good afternoon all.  With so many other distractions, not much has been happening on the bench this week ..but here's a little conversion I do to the oil filtration on my old Sunbeam motorcycle engines. . .


^ The engine block (in aluminium) with the original filter ..the oval shaped brass top with gauze mesh around it, soldered onto a base plate. This plate (when inverted so the filter is facing downwards) is sandwiched (hence two gaskets) between the block and the cast aluminium sump (top right).  The plate has a few through-holes, but they are not so large because it also serves as a baffle between the turbulence in the crankcase (with the crankshaft spinning around) and the wet-sump oil reservoir. It would helps stop the oil in the sump from surging forward ..away from the oil pump's pick-up pipe, under heavy braking.  'heavy' being a relative term with 1940's drum brakes,  but perhaps the oil surging sideways is also a matter for concern, when the bikes are used with a sidecar.

To the left is a (HOF306) disposable paper element oil filter ..which I now use, along with viton o-rings.  Seen at the bottom of the photo is a spacer made and supplied Stewart Engineering, who are the primary supplier of post-war Sunbeam parts ..and I believe owners of the Sunbeam Motorcycle name and its design copyright. The 'sump spacer' is supplied with new gaskets and  x12 longer studs. It cost the best part of £100 + p&p  ..but is (sort of ) useful because it increases the standard (3-1/2 pints) engine oil capacity by an additional pint.

However, the spacer fits between the baffle plate and sump casting, so unless one extends the pick-up pipe, that extra pint of oil just sits in the bottom of the sump. True it does mix in with the oil being circulated - but it does NOT  add to the oil capacity which is accessible to the pump. For example should the oil run low - the pump will still suck air (despite still having that extra pint in the sump).

Why is the spacer not fitted lower ..between the spacer and the sump casting then ?  Well, without extending its pick-up pipe down to the bottom - the pump would suck air at the same oil level anyway. The gauze filter is soldered onto the plate with a soldered-on collar to snugly fit to the pick-up pipe. It' not insurmountable but would need to be removed for an extension tube to fit through it.  And then how well would the plate work with so much engine oil above it ?   I suspect that oil would literally be driven up the walls by the turbulence within the tight confines of this crankcase.   So I change things. I leave the baffle plate where it was designed to be but I extend the oil pump's pick-up pipe.


^ This shows the standard oil pump's pick-up pipe relative to the inside of the sump  ..this is without x2 thick sump gaskets, the filter/baffle plate, or the after-market sump spacer.  There is about 1/4" between it and the bottom, but because of the notch in that pipe - the pump would suck air if the oil locally surged away to be less than 1/2" deep.

" Well that's a ridiculous low level of oil " you might rightly say.  But let's do the maths (on these little engines). We'll start with a (standard) full capacity of 3-1/2 pints, and then there's,  let's say, 3/4  pint of oil needed to fill the oil-ways, cavities and galleries throughout the engine,  and then when the engine is running there's another 3/4 pint being splashed against / running down the insides of the cylinder head, rocker cover, timing case and crankcase.  And the 1/2" air-gap between the sump and the top of the notch in the pick up pint constitutes another 3/4 pint, so also does the distance between the top of dipstick mark to the bottom mark (ie., conceivably less another 3/4 pint).  So we have 3-1/2 pints,  less 3/4,  less 3/4,  less another 3/4, and less yet another 3/4 pint = 1/2 pint reserve !   Is it not feasible that this 1/4 pint (= just 3/8" deep) might surge under braking or when a sidecar bike turns quickly through a fast corner ?  


^  illustrating the crankcase, and sump, relative to the length of the oil-pump's pick up pipe with the sump spacer fitted.  The shiny tube I'm holding up to it  is a length of aluminium which I'll use to extend the pipe by the spacer's thickness (21mm). 


^ The aluminum tube I use is an interference fit, on which I use Loctite but then literally hammer it on.


^ With the sump spacer in place, but still without x2 thick gaskets and the filter/baffle plate, I've reduced the clearance between the sump and the tube to about 1/8".


^ I then cut the bottom at a 45 deg angle so there's no restriction to oil flow, even if the tube should happen to work loose and drop down.


^ The pipe is now cut, de-burred and thoroughly cleaned out,  and I'm fitting the new / longer studs.

. . .

Moving on to the engine oil filter itself.. whose casing would stop my extended pick up pipe reaching the bottom,  and otherwise has too coarse a mesh to prevent fine contaminates (byproducts of combustion and running-in engine wear) from circulating. . .  


^ the solder around the front of this one happened to be cracked anyway.  


^ Blowtorch used to un-solder it.  I leave the two anti-surge plates in situ.


^ cleaning off the surplus - it's surprising how the weight of this adds up.


^ Ok cleaning up job done.  two new holes (red arrows) have been drilled and I'm just about to add a piece of aluminium angle - longitudinally to the top face of the plate.  This is to stiffen the plate against panting ..in a small crankcase which changes in volume by 500cc with every half revolution, and might also help with lessening the amount of oil being driven up the inside walls of the crankcase by the turbulence from the spinning crankshaft.

P1340112s.jpg.98533e4feaed1626f1d05122193315bc.jpg .

^ Here I'm checking a length of rubber hose I've cut to sit between the crankcase and the baffle plate. It effectively seals around the hole through the plate and acts as a spacer to (again) prevent that plate from panting. 


^ Working on two engines at once.  That on the left shows the extend pick-up pipe with rubber hose sleeve around it. And the engine to the right shows the sump spacer in place and illustrates how the disposable filter fits. (NB. old sump gaskets are only used for dry assembly trials, and not for the final build).   A fair bit of filing was done to have the plate and the sump extension sit down on the studs, as those (although original) are not perfectly parallel.  


^ detail showing my extended oil-pump pick-up pipe inside the disposable filter.  The cast finish on the inside of the sump (seen in first photo) has been locally smoothed, so the o-ring forms a seal between it and filter, which is sandwiched in there.  The baffle plate is of plated steel - so I'll also place a strong magnet on it. Because of it's size and shape, it can't go anywhere but in practice I've also never known one move about.   


^ The sump loosely dry fitted in place.  And unfortunately yes, the sump does have to be removed to change that filter, but so did it when needing to clean the original gauze.  Once after 200 miles of running in and thereafter every 3000 miles is not such an issue with a wet sump design. And of course, the oil itself may be changed frequently without dropping the sump. 


^ viewed of the aperture for the rear bearing carrier ..which also carries the oil pump and oil way galleries. The hole between the two studs at the bottom of this flange face is where the oil pump draws the engine oil from the sump, via the pick up pipe.  And the hole through the flange near the top is where the oil-pump sends the pressurised engine oil up to the camshaft.     Inside the case you can just see the upstanding length of aluminium angle used to stiffen the sump's baffle plate and to hamper oil being driven up the inside wall of the crankcase.

In this morning's post I received a second sump spacer from Stewart Engineering, for the other engine. . .

P1340120s.jpg.642826838d7b715c1845214349e45edf.jpg .

^ Actually it's a nice casting, but their instructions neglect to say it needs finishing.  It's a raw casting and so the gasket faces are not smooth, and more often than not these castings are not flat ..but is often slightly bowed &/or twisted - so it needs flattening on both sides before it will be oil tight.  Often the holes need easing too, but that's because these Sunbeam engines were made on 'very tired' war-time machines. 

Personally I also find they look slab-sided when fitted - and so, as you see in the other photos,  I file a grove all around it's outside, which (visually) halves its height and imo compliments the lines of crankcase cooling fins.

That's it for today - it's time for me to do some flatting and filing !

Best regards and take care,



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This afternoon I carried on from the above  ..catching up on the second engine. . .


^ the problem with studs is that if any of their holes have been drilled off-perpendicular to the gasket face,  then the stud either splays sideways or in or out ..relative to the others. Then the sump &/or sump spacer wont go over them. Of course the longer the stud is.. the more out of true alignment their free ends are.  Mostly this can be corrected by judicious filing of the holes in the sump and sump extension . . . 


^ The red felt pen ticks indicate where the stud fouls in the hole, in this case - preventing the sump spacer from going on.  So here (in this photo) I'm using sideways force on the drill-bit to ease the hole in the direction of the tick.  The sump spacers have slightly oversized holes., but even so they needed filing or in my case drilling sideways to make it fit.  The sump I'm using was not original to this engine, and its drilled holes were a tighter fit to the studs, so a time consuming amount of rework was needed. . 


^ this particular stud's hole was drilled n' tapped at slightly the wrong angle, whereby the free end of the stud was out of alignment by over 1/16" (1 - 2mm). After fitting and noting which way it fitted in the hole - I took it out again and bent it !  


^ This is that same stud, now refitted, and you can just about see how it's bent  (the shape did sprung back some, after being altered in the vice).  The end tip of the thread is now in alignment with the others, but of course it is still bowed out ..but by only half as much as its end previously was !


^ It took me a couple of hours to alter the spacer's and sump's holes to fit over these crankcase studs. Even now some are an interference fit - but those parts can be wiggled off by hand, rather than needing wedges to free them.  Once in place there's just a little slack on the studs - so the crankcase's holes were all drilled in the right place ..just not at the right angle.  

That part of the job is now done, but to my eye the spacer looks slab-sided and ugly,  relative to the otherwise beautifully sculptured crankcase. . .


^ pencil marked where it is to be cosmetically altered  . .


^ carefully shallow cut all the way around,  except in the area of the sump's drain plug.  I don't do that place - simply to indicate the spacer's correct orientation.  If fitted the other way around - my filing of the holes doesn't then suit the stud pattern and the sump outline shape won't align so neatly with this spacer ..as its holes have been drilled just little towards one end. 


^ widening that hacksaw blade cut with the corner of the file to form a v-shape groove.


^ and then rounding that v-shape groove into a shallow U shape.  The finish isn't critical. In fact any neater and it looks worse !  ..because the castings of the engines cooling fins are likewise never perfectly straight nor smooth.  


^ that's it.  A whole lot of work to file a shallow grove around the slab face of the spacer.  The proportions are reasonably compliment to the spacing of the engine case cooling fins ..and so after a few months on the road (when all the aluminium has oxidized to the same  colour) then it will not even be noticed.!  But to my mind - it is the details that you don't see which can make the difference between something looking right or something looking just a little odd.  

Enough of my prattling on today.  I bid you a good evening.



Edited by Bfg

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Me Big man.. me make big mess in kitchen !


^ a quick check for flatness of this sump's gasket face reveals a corner not sitting flat by 0.003". 


^ 320 grit wet n' dry taped to the flattest part of this kitchen worktop ..and with a little elbow grease + soap n' water - its gasket face was trued up a little.


* I use a felt pen (waterproof ink) as a very convenient substitute for engineers blue.  It works well.


^ the sump's gasket face is now very flat aside from a dint ..right next to the middle stud hole in its forward end (to the right you can see what looks like a black dot).  As engine oil might seep passed this and out through the stud's hole - I'll fill that dint with a spot of Araldite.   The new spacer was as flat as any I've yet bought and was generally fine after a few minutes work, aside for a slight low cut (see blue across either end). It been milled but this one cut was perhaps a thou deeper.  A bit more work on the wet n' dry pad took the surrounding aluminium down so it's barely discernible now.

So I moved over to checking the rocker cover's gasket face and that of the engine's timing chain inspection cover.



^ the rocker cover I had done before and so this was more a check than anything.  And this particular cover is in excellent condition.  Sadly I've come across so many which have been abused over the years with careless handling, over tightening of the three studs (which cracks the casings and then need welding), and most are badly bowed. Some I've known to have 0.035" or more distortion.  This one shows a little hogging, but it's now less than a thou, so as I double up on the card gasket I use here - I'll leave it as is.

The gasket face of the little inspection cover though is pulled down at every fastening hole.  I could slip a 0.006" feeler gauge inbetween the worktop and gasket face, in the short span between the holes. That's more than the gasket can take up, so it must have been leaking badly when last use.


Awkward little so n' so to hold down and rub against the wet n' dry., but little by little it succumbed to the threat - be flat or be scrapped !


So, only an hour of work today ..but an hour in the right direction is better than non at all. 

......even if it take me a further half an hour to clean the kitchen again !  :wacko:



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Just two to three hours yesterday to quickly report on. .  


^ For a 1953 motorcycle engine these bores, lightly de-glazed with fine-grit wet n' dry, are in remarkably good shape - not least because they are still to the original standard size.  But as you can see from the photo they are worn.  It's more visible than a hard edge, but measurements suggest there's 0.004 - 0.005" of wear.  The vertical scoring lines are visible but are so shallow as to be immeasurable and not felt ..so perhaps just 0.0005 - 0.001".? 

The 1/4" high rim around the top is where the piston rings (which are situated part the way down the side of the pistons) don't wear.  The darker colour immediately below this is where most of the wear occurs because that's there the top two compression piston rings come up to and as the conrod sweeps over tdc they stop and cock sideways a little ..and then under the full explosive power of the combustion are pushed about and accelerate away again.  And of course, near the top of the compression stroke the cylinder is densely packed of air-fuel mixture, and the latter part of this dissolves lubrication on the cylinder walls.

In the present circumstance of our country's lock down I can't just take the block in to the machine shop and have these rebored to +0.010", so I'll just replace the piston rings and use things as they are. Let's face it., this bike will probably not average more than a couple of thousand miles a year anyway ..so it will last another 10 years without issue, by which time I'll be in my mid seventies so I won't worry too much about squeezing every last ounce of performance. 


^ here I'm using a Dremel with small sanding drum to reduce that rim's step-height.  The primary reason to do this is so the piston rings, when correctly sized (tight) to the slightly worn bore, will also slip passed this lip as they are fitted with piston into the cylinder.  Even if a remnant of the lip remains and it's rough - it'll not be an issue because the pistons and rings do not run on that short length.


^ I then used a honing tool to de-glaze the cylinders.  The very fine scoring the stones produce helps retain lubricating-oil as the engine is run in, and also help the new piston rings to bed in (wear to a very snug fit). 

With this tool, I use a cordless drill at its slowest speed (controlled by trigger pressure) and at the same time I bob it up & down ..so that scoring is at an angle to the piston rings (rather than straight the way around - which would tend to snag the rings).  I use thinned engine oil (50 / 50 new engine oil to engine parts cleaner) as a cutting lubricant.  Aside from clagging, this stops the grindings of metal and stone becoming airborne dust, so although it's messy - it can at least be seen, contained and more easily cleaned up.   Naturally it has to be thoroughly cleaned from anywhere within the engine before reassembly.   


^ New old stock Hepolite piston rings versus Italian made ones.   oh the nostalgia in old packaging. I love it. 


^ interesting that it says Sunbeam 1946 / 52, when these bikes were made through to 1956.  Perhaps these piston rings were made in 1952 ?  I also love the long-hand £-s-d arithmetic scribbled on the back of the packet. 

"Ring gaps should never be less than 0.003" per inch of bore diameter, or for racing engines 0.005" per inch measured in an unworn portion of bore" is interesting because the Sunbeam manual specifies 0.004 - 0.006" for its 2-3/4" bore.  (Hepolite figures being 0.003 x 2.75 = 0.00825").  Personally I've found from experience of these engines that too tight a piston & rings tend to seize during the running-in period, so thereafter I used 0.008" for the top compression ring (which gets hottest) and 0.006" for the other three. Perhaps I ought to up my figures.  The Italian piston rings don't specify any fit, but I might only presume they would expand as much as the Hepolite rings ..despite their being much softer steel  (..evident when I was filing their length and also in their springiness). 


^ I use a short bolt as a measuring stick to accurately position / level the piston ring all the way around - a set distance down the bore.  The length of this corresponds to the level of the top oil scraper ring on the piston, and this in the bore is hardly worn.  The overlap of my 0.010" oversized rings is then marked using a fine felt pen. . .


^ and then that is filed down (using a square sided wooden block to help keep my filing true / square).  It's a time consuming task filing (deliberately cutting too little) then repositioning the ring back in its bore to recheck the measurement and also that the filing is square ..to the nearest fraction of a thousandths of an inch, with feeler gauges (below) and then filing a little more, re-measuring again, filing some more, and so on ..until the gap is spot on.   

BTW, the ' T '  I mark on these is simply to more clearly highlight which is the top face of the ring (the sides have a slightly tapered angle), and then I only ever cut / file the other end of the ring  ..only one end is ever touched so needs to be kept square.   


^ checking the end gap with feeler gauges.  

Tip ; even with freshly rebored cylinders there's always a slight difference in diameter of the bores. It may only one thou of an inch (machining tolerance) but as a perimeter measurement (which is what the ring's end-gap is measuring) then that 0.001" difference in diameter = 0.003" difference in end gap.  So it is good practice to measure and file your rings for the larger diameter bore.  And then if you file a tad too much (perhaps if that cut didn't go perfectly square and you want to true it up), then you can use that ring in the other / tighter bore.


^ these are the Italian rings, each measured and carefully filed to size.. Each is marked to indicate which cylinder, and which piston's ring position it is to fit into.  I've cut these all to be 0.005" end gap in accordance with the Sunbeam Workshop Manual (seeing as these bores were already worn near their top) but after reading the instructions on the Hepolite packaging, I think I'll go back and ease them just a little.



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I was asked whether the bore wear was even in the two cylinders. On these engines it does tend to be.  But contrary to the obvious - the forward one runs hotter and is more prone to seizure.  I'd suggest the reason for this lies with its design utilizing the oil  (return from the camshaft) running down and splashing around inside the cam-chain chimney ..which in turn dissipates heat from the rear cylinder's casting to the aluminium cases including that of the bell housing - that acts as a massive heat-sink.   So whereas the forward cylinder has relatively thin cases and mostly relies on air-flow past it,  the rear cylinder relies on the excellent conduction properties of chunky cast aluminium to transfer the heat away.  The heat management / balance of these engines is imo very clever.  Of course the real 'hot spot'  is the rearmost segment of the forward cylinder where the heat between the two cylinders has almost nowhere to go. ie. the most common seizure is just above and below the gudgeon pin on the rear face of the forward piston.

- - -

  This afternoon I was doing the same (piston ring gaps) on Pudge's engine.  


^ This was easier and quicker because it had already been rebored, so no rim around the top of the cylinders and no wear immediately below that ..so the bores are almost parallel sided. The rear cylinder is however one and half thou smaller in diameter.   That's a little odd, if only because some machine shops anticipate the rear cylinder running hotter and so leave a little extra room for expansion.  But this one is to the contrary. 

Anyway no lip meant that placing the piston rings in to check / measure them was a swifter task, because I only needed to aligned them just inside the top. Only when fine fettling the finished end gap size did I position them further into the bore.. Then I used the thickness of a nut as a 'measuring stick' for the compression rings (..so that positioned them about 1/4" down the bore), and then the same short bolt as used previously as the measuring stick for the oil-scraper rings  (.. so those rings were eased 5/8" down the bore).

I did have to be careful though because those Hepolite piston rings are very hard and brittle ..needing to be handled with extreme care.  The difference is that they are cast iron which I presume were then machined before being surface hardened.  Cast iron makes a very good spring which is also very hard, but you cannot bend it very far at all.  The Italian piston rings are most probably made by rolling high carbon steel, which are then machined to shape, again before being surface hardened.  The rate of springiness is less but they bend more easily and so are much easier to handle, without breaking.  Same job but very different characteristics.

Anyway that job is now done, with my following the end-gap guidelines set out by Hepolite (so ignoring what the Sunbeam Manual says). All these rings are set to 0.008".

- - - 

As an aside, I guess this is an opportune moment to briefly discuss removal and refitting of rings to the piston.  Many of you will know how best to do this,  so it's just a guide for those who are new to tinkering with old motors. .


^ Bottom oil scraper ring ..also known as oil control ring(s).   The oil scrapers are wide and have double blades to scrape oil around the piston (see its  shiny edges above).  I gather most people think of an oil scraper / oil control ring's job is to stop oil from the crankcase getting passed and up into the combustion chamber. But that's mostly not their purpose.  Actually the piston has numerous drilled holes within this groove ..purposefully to let oil into the gap between the two blades. And then as you can see there are more holes drilled between the two oil scraper / control rings fitted to these pistons.  And so the rings are like oil galleries ..to route / transfer lubricating engine-oil all the way around the piston skirt and the cylinder walls.  NB., unlike these solid but slotted piston oil-scraper rings (seen above) - modern ones generally have two blades and a corrugated style of spring inbetween them (to hold the blades square / in place).   But the same principle applies ..of letting a controlled amount of oil splash and oil mist from the crankcase through to lubricate the piston running up and down in the bores.  

Anyway because these solid (rather than spring) oil control rings are wide  (almost square in section) - they don't easily bend or twist.   So (above) you can see me using two old feeler-gauges to slip between the piston and the ring.  I carefully lifted one side of the ring out of its groove, and slipped in one of the feeler-gauges to suspend the ring above its groove. I then slipped in a second one ..and carefully worked that around to the other end of the ring.  Some folk slip in a third gauge, to hold middle of the ring out of the groove while the first two are eased towards (and therefore lifting) the ends of the ring to very gently lift them out of the groove.  The ring is then slid off the end of the piston.


^  Personally I prefer not to use a third feeler gauge, but instead I carefully twist / ease the ring over the bottom of the skirt - so it can curl inwards to a smaller diameter (..less stretching to the limit) .


^ I do the same, gently twisting over the end for the top piston rings.  I find the sideways flex is more forgiving (less breakages) than stretching the ring outwards all the way around to the much bigger diameter. 


^ however the top oil scraper / control ring cannot twist / sideways flex enough, so for this one it is a matter of inserting the feeler gauges ( 0.008 - 0.012" thick ones work best) and very gently easing this ring outwards so it might be slipped upwards and over the two compression ring's grooves. 

Fitting piston rings is a reverse procedure.  I fit this top oil-scraper before any of the others, by resting one end of the ring onto the side of the crown and gently pulling (springing outwards) and curling / twisting the ring onto the feeler gauges, before sliding it down to its groove.   And then the feeler gauges are moved around ..away from the ends (one at a time) so the ring's end eases into the groove.  It is a task that might benefit from having three hands (..together with a fair degree of patience) but of course is manageable on your own.  If in doubt.,  practice with the old (worn out) rings before trying to fit brand new ones. 

It's really as simple as breaking twigs.  

.               Argh.. did I just say that out loud ! 


With the old piston rings carefully (..I never know when I'll need a used one - in case one of the new ones darn-well breaks !) removed,  I could clean up the pistons ready for fitting with new rings (already perfectly sized to each bore). . .


^ Just so many oil holes through those pistons !

Hopefully from a quick glance you'd never guess these were very old pistons ..that had been up n' down tens of thousands of times before.  I even polished up the gudgeon pins (..still a good tight fit).   Tomorrow I'll do the same with the other engine's pistons.


That's it for now folks.  Take care and a very good day to you all.


Edited by Bfg

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evening all.,   This afternoon's task was to weight match the pistons and rods  ..after cleaning up the second engine's pistons and rods.! :blink:


^ Standard size and in really good condition.


^ after general cleaning I set to with cleaning out the crud from the grooves, using a needle file. almost no pressure is required after all I'm just removing the oil deposits and don't want to cut into the aluminium itself.  Another time consuming task ..but tbh I couldn't bothered to get the de-carb acid out.  


^ again carefully cleaning out the burnt-on oil crud out of the oil drillings (..my last post which explains why).  I'm using a 2.5mm drill bit here, and many were blocked to less than 2mm.


^  Those in the skirt,  rather than in the grooves, are at an angle.   There's also a couple more to be cleaned out inside the piston (of 3mm size) which are to lubricate the gudgeon pin. 


^   #1 cylinder's piston has light scoring and pitting (from heat) from where it had seized at sometime (..perhaps when new).  It's usual and this is as good as the best I've seen ..and certainly redeemable.


^  yes I'm a butcher !! .. I used a power file to linish it down a little


^ ..and then 400 grit wet n' dry to smooth it again.  That'll be just fine.


^ it's difficult to see from the photo but the (+0.030") piston on the left, which is from Pudge, has a much rougher internal casting with cast-in part numbers ..and their wall / skirt thickness is perhaps twice as thick as the standard size piston from Nudge.   Of course with it being oversize I cannot even guess its age.  

I checked the weights of these and found them to be pretty darn close.  The naked pistons were 243.3 and 242.2 grams respectively and their rods with big end bolts & shells were each 342.4 grams.  I'd say that's pretty good for a 1950's vintage road bike.  However the gudgeon pins were odd. One was 74.7g and the other 64.6g.   

The standard sized pistons from Nudge's engine were 20g lighter but not quite so well matched at 214.1 and 220.0 grams respectively. Its rods (again with bolts and shells) are 349.6 and 351.9 grams respectively.  Perhaps tomorrow I'll see if I can lessen those differences a bit. Again the gudgeon pins were odd, as if they had been mixed up between the two bikes ..which I can assure you they were not. But they were similarly out at 66.7 and 75.7g respectively..  Coincidental but a very similar difference in mass to those from Pudge's engine.

I have a spare set of pistons and rods in my shed, so pulled the gudgeon pins from those  . .


^ gudgeon pins (in order) from three engines.  Despite it being heavy-weight, the first from Pudge's engine is 1/16" shorter than any of the others. The third pair (right) are a matched pair at 61.0 and 61.3g respectively.   I'll use those for one engine and the other two lighter ones for the other.  They are all a good fit anyway despite there being no little end bearings on these bikes. I guess they are so lightly loaded with either 6:1 or  7:2 compression ratios. 

So that's it for today ..


Have a good evening.


Edited by Bfg

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..just finishing up on balancing the weights of piston gudgeon pin and con-rods from yesterday.  .


^ I started off with ; pistons 8g difference in weight, and a pair of gudgeon pin 2.2 difference in weight.  Matching the heavy piston to the lighter con-rod, and vice versa (as above) still left me with 5.8g difference.   The lighter gudgeon pin looks to be the heavier (above right) but it is straight drilled through whereas the heavier one is drilled hollow as a taper from either end, so is thicker in the centre.    The pistons themselves look to be very similar indeed, and I know that 5.8g of aluminium is physically a lot of metal to remove, so removing that much wasn't really an option. 

Conversely because steel is that much denser I need take less out of the gudgeon pin to achieve a better saving.  So that's what I did.  Starting with the already lighter pin I wondered if I might work the hole through it to be a taper ..and the metal removed would be the weight saving I sought . .

.    P1340250s.jpg.a9c09e886b6a84ae0a7239b3f74d0fcc.jpg

^ I didn't honestly think it would work, gudeon pins being hardened steel an all,  but I tried to used a burr bit in my cordless drill.  Despite that bit being old and well used (seeing much use in my fibreglass boat) - amazingly it did cut this steel.! 

I steadily worked my way around the inside of either end of this pin ..which did take me three hours,  but yes - it worked. 


^ the pile of grinding is testimony to that. I took 4.6g  out of it *  ..just in tapering the hole from either end. This brought the gudgeon pin down to 61g which is the same as those I'm using with Pudge's set of pistons & con-rods.  My reasoning of course was that ; if just this amount of metal is good (from standard) with the other gudgeon pins, then it ought to be equally as safe to use in this engine.                                     * for reference a 5/16" weighs 5g


^ That's it.. I took just 0.2g out of the heavier piston which brought it down to 221.7g but paired with the 61g gudgeon pin their combined mass is 282.7g.  And this is now just 2.4 heavier than the lighter piston matched to the heavier gudgeon pin.  

And then, pairing the heavier of these with the lighter con-rods for that engine, and vice versa.. there is now just 0.4g difference in their total weight.   

I can happily to accept that.   Job Done.!

Cheers, Pete.

Edited by Bfg

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Hi Pete , don't know if you noticed but on another thread by Pete Fenlon (Engine advice pls) there is a photo showing his crankshaft and on the journal you can see where an aggressive balancing grind has taken the journal shoulder down very low (maybe lower than yours) which may point out that they still work ok when lightened to that degree. Might be a comfort to you.

Mick Richards

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34 minutes ago, Motorsport Mickey said:

Hi Pete , don't know if you noticed but on another thread by Pete Fenlon (Engine advice pls) there is a photo showing his crankshaft and on the journal you can see where an aggressive balancing grind has taken the journal shoulder down very low (maybe lower than yours) which may point out that they still work ok when lightened to that degree. Might be a comfort to you.

Mick Richards

Thanks Mick,  Yes indeed.  I haven't had mine checked yet ..due to the restrictions in place, but Pete Fenlons looks to be very similar to my own (now).  I spoke to Richard Coles (Coltec Racing Engines, Hollesley, Suffolk) and he'll check mine as soon as we get back to normal.  Would such grinding not imply that Pete F's crank had also been re-balanced ?    

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4 hours ago, Bfg said:

Thanks Mick,  Yes indeed.  I haven't had mine checked yet ..due to the restrictions in place, but Pete Fenlons looks to be very similar to my own (now).  I spoke to Richard Coles (Coltec Racing Engines, Hollesley, Suffolk) and he'll check mine as soon as we get back to normal.  Would such grinding not imply that Pete F's crank had also been re-balanced ?    

Yes Pete, that's what I thought. I don't think Peter has run his engine (or if so only briefly) but I hope it is good news and both cranks are ok.

Mick Richards

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a week on from my last post., when I was matching the weights of the pistons and rods and carefully gapping the piston rings ..


^ dry fitting the con-rods, with new shells, to the crankshaft to ensure all was well. It was ..but for a slight confusion . .


^ you note #1  con-rod had at some time also been stamped on its other side, so when I first fitted this cap it happened to be on back to front front - so not quite true and binding.  It was soon spotted and corrected though, and I've subsequently scoured across these back-face marks to avoid making the same mistake when working inside the crankcase.


^ No it's not a double-crankshaft four-cylinder engine but two twin-cylinder engine being worked on at once.

On the one crankshaft (that at the rear) you might have noticed ( to the rhs) a large screw plug hanging out by its front journal. . .


This 1" screw / core plug closes off the large drilling inside & between the two big ends.  It is designed to come out - so the inside oil gallery can be properly cleaned out. Because that is a centrifugal oil filter..  As the crankshaft spins ; heavy particles within the oil are naturally thrown outwards by the centrifugal force, and eventually build up in there as a very tightly compacted sludge.  The drillings into that gallery for lubrication to the big-end shells are so positioned to allow that 1" dia x 5" long space to be half packed before the oil flow is in any way restricted.  And if the oil is changed frequently - that equates to a monster mileage.  If however oil changes are neglected and filthy heavy black oil is spun - the plug needs to be pulled and the compacted sludge gallery chiseled out.  .. yes it gets that hard.! 


^ the professional who pulled this engine apart removed most every stud and every plug in every part, even though that was neither necessary nor useful. 

What's the big deal with taking everything out.?  Well I come from the perspective of not disturbing things which need not be, unless not touching them is detrimental to the long term well being or reliability of the engine. ..for example ; old oil seals. They may seem to be in good shape but because of its age and their perishing - they ought to be changed.)   Conversely a fastening into the engine needs not be disturb unless it is weak or because the flat is needed for machining.   In this instance a large roller bearing overlaps the core plug and so that needs to be removed first ..and because there is no space behind it to get a decent puller in - they are more often than not damaged.  At £89 +P&P.,  unless it is needed replacing (very rare on these engines) then why risk it ?


^ Before pulling the bearing and taking the core plug out,  you can easily check whether it is necessary to do so.  A curved piece of wire simply poked through the big-end oil drillings can be used to feel if there is a build up of sludge in there. Without packed sludge the wire feels the smooth, hard metal side walls. But if it is full of crud - then the feel is dull and the wire digs into in the surface. 

A parts washer (pumped cleaner) can be used to wash through from the three oil-way drilling to ensure no loose bits are in there.  I left one running overnight because what was inside was soft sludge. And after 14 hours of being pumped with parts cleaner it was fine. 


^ It took me two hours to get this thread needle-filed clean enough to go all the way back in.  


^ before refitting the plug I did however check the drillings for the oil-way to both big-ends was clear.  It was mostly but the correct imperial size of 7/32" revealed it not having been properly cleaned out.


^ Likewise the drilling from the rear main bearing carrier into the crankshaft's gallery. This was furred up a little more ..right near the bottom end, as if someone had run a 5mm drill down into it but even that drill wasn't long enough.  It needs to be the same 7/32" imperial-sized drill which protrudes at least 2-1/4" from the chuck.  Having stripped the engine this far why not just do it ?


^ when the plug's thread is clean and refitted with medium strength Loctite - it does not need to be peened with a centre-punch to lock it.  Btw. you cannot peen the forged steel crankshaft as that's too brittle a material and its edge will tend to crack off. .  

With that done I refitted the studs into the crankcase. . .


^ the studs had their threads checked and then dry fitted first, also cleaned up of gouges where the grips had been used on some of these studs, before being refitted with Loctite.  Again only if necessary are the studs replaced ..as I better trust the quality of the original parts over a replacement.

More to come later with the rear bearing assembly and oil pump, and also trial fitting the cylinder head. .



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as I was saying ...the rear bearing assembly and oil pump, and also trial fitting the cylinder head. .

well ok then, but in reverse order


^ Ok no head gasket is fitted but if it doesn't sit down and be reasonably flat ..what hope is there ?


^ I don't know who but someone previous replaced the two rear outside studs with stepped /shouldered ones.  That is, their 5/16" BSW holes have been tapped out to be 3/8" and an aftermarket stud fitted. That's not terrible, although I personally prefer to use helicoil type thread inserts, because they cut less metal away in the aluminium case. However these were screwed in as far in as their hole allowed and that wasn't enough.  In retrospect, I should have taken the thread out again and cut their threaded length down, but instead I countersunk the holes in the underside of the cylinder head, just enough ..perhaps 1/16", so the head would then sit down.   A little scraping with a craft-knife blade flat on the gasket face removed the slight stretch around the studs fitted into the cylinder head. The gap is now less than my feeler gauge so a head gasket will take up any more.  

Tbh., the three 5/16" studs, around the timing chain chimney, barely do anything compared with the nine 3/8" cylinder-head studs.  I guess they are there to help prevent the corners from lifting and so distorting. 

However, the workshop manual says to tighten the main cylinder-head nuts with two spanners (one interlocked to the other ..to double their leverage), but it doesn't exclude nor mention how to tighten the three smaller ones ..which of course strip out with that amount of applied force.        

- - -

Moving on - Rear bearing carrier and oil pump . .


^ The rear main bearing carrier is of cast iron with the white-metal main-bearing pressed into its centre. The crankshaft end float is determined by a flange on the back face of this bearing. The geared oil pump is machined into this casting, which is also drilled with oil ways ; from the sump's pick up pipe, to the rear main bearing (..and crankshaft),  to a machined-in oil pressure control valve (situated to the left of the pump), and to lubricate the spigot (at the top) which carries the geared cam-chain timing wheel (..that has the chain sprocket on its reverse face).  At the top, in its rear face, is an oil-way drilling to the crankcase which leads up to the cylinder head which likewise is drilled to the camshaft and rockers.   So really it is a brilliant piece of (lubrication) system design ..with all but the pipe from the sump and the drilling to the camshaft contained in this one part.


^ the components of the oil pump, which as you can see has had it cover (bottom) leveled. The gears themselves just drop in but any end float in those needs to be taken out by removing the two studs and milling the face of that housing. 


^ These gears had a couple or three thou of an inch end float (seen as light through the gap above) ..and I don't have a milling machine. But I did have that craft knife blade and found by scraping that there was a tiny lip around the machined hole ..and with that carefully scraped flat - it removed the gear's end float completely. I was lucky with this one.  

I physically blow into (pressurise) the oil pressure valve ..with just its ball (no spring) in place.  If that ball seals the air-flow when dry of oil - then it's fine for service. 

The pump and its pressure control valve were refitted, checked to be within fine tolerance, and oiled.  I also checked the rear main bearing dry fit onto the crankshaft - it to ensure it was exactly the right size.

- - -


^ It's not what it seems !       My next job was to ensure that the inside of the block was thoroughly clean, and so I poured clean petrol through the orifices..  Inverted it and did it again.. Stood it on end and washed it out yet again.  Without any oil (or even oil residue or staining) facilitating "bits" sticking to the inside of the case, I'm satisfied that its clean and ready for reassembly.  That is after it sat out in the sunshine and light breeze to dry out. I have enough stink of petrol over me that I don't need to bring more into the house !

- - -   


^ speaks for itself, so I'll shut up (for a moment !) 


^ front roller bearing was liberally oiled before assembly. The bearing outer just sits in there against a circlip in a sleeve which is part of the crankcase.


^ look Mum.. no hands !


^ up ended for convenience of fitting the rear main bearing carrier. 


^ Likewise the rear main bearing was liberally oiled.  


^ being very careful not to catch that white-metal bearing on the hard edge of the crankshaft.  They damage easily and bits can chip off.


^ and there we are. The crankshaft is now in and the rear bearing carrier fitted and tightened evenly ..but with those nuts sitting on plain washers just for the moment.  


^ checking end-float of the crankshaft at the rear main bearing. It's awkward to get in there with a feeler gauge but this 0.003" gauge is just fitting.  The spec says a minimum of 0.004"  but I learnt a while back that it's not so critical. This is because thermal expansion of the alumunium crankcase is more than that of the steel crankshaft ..so as the engine gets hot then this gap will increase.  In the meantime anything more than 0.002" will be sufficient for the thrust bearing's oil lubrication. So with 0.003" I'm happy not to pull it out ..just to scrape another one-thou off its white-metal arse.!

The bearing carrier's plain-washers were subsequently changed for split washers (I believe star washers were original ..but I hate those things), and the nuts were refitted with medium-strength Loctite.  Although there's no specification for their torque - I did these to 12 ft lb., as I like things to be evenly loaded.   

Well I think that'll do for now ..so again I'll come back later with a further update..

Bidding you a good 'un - on this gorgeously mild and sunny spring day.



Edited by Bfg

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With the crankshaft and the rear end main bearing now refitted . . .


^ the components of the cam-chain tensioner blade and its bronze bush.


^ because the engine case limits fitting clearance, the blade is fitted first and then the bush (which is a sliding fit) is popped in.  Naturally, to get the blade out is the reverse whereby the bush is lifted out before the blade.. That's not intuitive, and clearly from some of the damage I've seen on other engines - some prior-owners simply didn't get it.!


The blade and its bush are retained on the pin with a sprung plate. One end sits directly onto the nut of the rear bearing carrier stud, and is fastened with another 5/16" nut.  Although it has its own lock washer - I still use Loctite on the thread. The other end of the plate has an elongated hole, as the plate sits astride the pin - so the spring bears on the blade and its bush.  Again beautifully simple, super reliable and easy to fit.


^ the valve timing is via this gear with sprocket (also referred to as a "half time gear"). It of course carries the timing chain which loops around a sprocket fitted onto the end of the overhead camshaft.  The gear has a bush within it, and this and the spindle need to be a nice sliding fit (not wobble). The spindle is pressure fed with engine-oil but they seem to wear more than most other parts on these otherwise unstressed engines.

New ' half-time-gear-spindle' and bush are available from Stewart Engineering, Poole, Dorset.  And for the best part of £75, for the pair - they are not cheap ..but a wobble free fit is required to avoid twist and therefore excessive wear in both the gear and chain, and more importantly - so the engine oil's pressure is not lost through / passed the spindle.  Both bush and spindle are an interference fit in their respective parts, and so need to be assembled using heat and a press (a vice will suffice as long as its jaws are square as it squeezes together ).   The spindle is drilled for the oil way and this needs to be carefully aligned before it is pushed in. Check the orientation after fitting by blowing through the hole to ensure it's clear.  The spindle should also be pushed in so there's minimal end float between the gear and its retaining thrust washer.


^ As stated above, there should be only a tiny amount of end float of this gear on it's spindle.  Measuring this., I found it to be 0.015" ..which is too much to retain the lubricating oil.  However., with a confident tap squarely on the end of the spindle - it went in ..and this end float is now 0.002 - 03".


^ The cam-chain has to be assembled onto the sprocket and fed through the engine case as the timing gear is fitted. The original timing chains were endless, but most replacement chains have a link, and this link ought to be pointing in the direction of rotation so its tail-ends cannot snag. Please see small red arrow next to the chain link in the photo above (that link is also seen below).


^ The timing cover (which I'll be fitting later) is secured by ten screws, and the top one (which I'm seen holding) is extra long - so it protrudes into the cam-chain chimney. This thoughtfully little detail prevents the chain from slipping down and getting tangled.  You might also note that I've temporarily wired a couple of the chain links together, so even the top loop of chain cannot drop passed that screw as I turn the block upright.

Small details but a little forethought helps subsequent assembly.

More to come later. Happy Easter - Pete.

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