Liner Protrusion

[PeteT]

Hi guys,

 

Yes I guess it's a spectator sport. Mick - no I'm afraid I didn't put the head and old gasket on before I measured. I can't see how doing that would affect the deck height ie the height of the piston crown in relation to the block surface? I can see your point about using the head and old gasket to squeez the liners down.

 

Regards,

 

Pete

Edited May 12, 2015 by PeteT

[Rob Salisbury]

ntc.

The old head will be not be flat even if it has been skimmed

Thanks for that Neil, not sure I'd agree after being skimmed, I'd hope the machinist was able to get it flat, but you never know!!

Cheers Rob

[Motorsport Mickey]

Err...if your liners squeeze down by .002 thou then the piston to deck height is reduced, the pistons being fixed in position by thecon rod length and the throw of the crankshaft journal.

The head sits upon the liners and gasket and is your effective deck not the block surface which can be up to .005 thou below that ie: the liner protrusion.

 

Mick Richards

Edited May 12, 2015 by Motorsport Mickey

[PeteT]

Thanks Mick,

 

That's interesting. I've never read or thought that the head surface was effectively the deck height for the Pistons. I can see your point. So once I've taken all the squish out of the soft copper seals the measurement I'm looking for is the residual liner protrusion plus the squashed remains of he gasket?

 

Regards,

 

Pete

[BlueTR3A-5EKT]

Yes and if I remember correctly 0.040" is a good measurement to aim at, as the 4 cyl TR is quite a 'flexible' engine - Correction please if any one has a better figure.

 

That's the piston to liner top plus the squished gasket.

 

Get it too small and the pistons whack the head.

 

 

Peter W

[Motorsport Mickey]

I work on 40 thou on standard composition copper gaskets.

 

Mick Richards

 

PS: Just thought, check out the Technicalities CD, good information on CR and compression heights on 4 cylinder engine.

Edited May 12, 2015 by Motorsport Mickey

[Guest ntc]

Spot on Mick and thanks,all a waste of time if the old block is knackered and pitted remember how old they are.

[PeteT]

Hi Mick/Neil,

 

Ok I have just been through the process you outlined above with the following results:

 

Liners - measured at four points average .005-6 thou.

Height of piston below liner top .003 thou

Old gasket thickness average is .0036 thou

 

So to my feeble calculations the piston deck height using the cylinder head face as the reference point is .0039 thou. Any good?

 

Regards, Pete

[BlueTR3A-5EKT]

Hi Mick/Neil,

 

Ok I have just been through the process you outlined above with the following results:

 

Liners - measured at four points average .005-6 thou.

Height of piston below liner top .003 thou

Old gasket thickness average is .0036 thou

 

So to my feeble calculations the piston deck height using the cylinder head face as the reference point is .0039 thou. Any good?

 

Regards, Pete

That'll do for an engine you do not intend to use in competition -

So what were the cylinder head combustion chamber capacities, so you have an idea of what compression you will have?

Then get it built and start enjoying the sunshine.

Peter W

Edited May 13, 2015 by BlueTR3A-5EKT

[PeteT]

Hi Peter,

 

Few! That's a relief. I still find it interesting that if I was using the 'textbook' reference point of the block face, I'd be hacking lumps off the tops of the Pistons. With regards the CR, I found a section in the technicalities CD that confirms that with the 87mm conversion on a standard low port head the CR rises from 8.5 to 9.5. Which sounds ok. I guess this conversion has been done so many times that the path is well trodden.

 

Regards, Pete

[BlueTR3A-5EKT]

Measure the chamber capacity to be sure or you could end up needing 5 star plus octane booster. Reading what you have done and the bits you are using, you are unlikely to have an engine so flat you wished you had bought a crippled slug.

 

 

 

See Minty Lamb

 

http://www.mintylamb.co.uk/?page=measurecc.htm

 

Peter W

 

PS The confusion you suffered is that the 'deck' is the highest point of the block. In the case of a wet liner TR the block includes the liners, which protrude. Therefore it is the distance from liner top to piston crown, once the liner is seated correctly in the block.

Edited May 13, 2015 by BlueTR3A-5EKT

[PeteT]

Thanks guys,

 

I'm off down to the chemist tomorrow and will be checking the combustion chamber volume. I will use a CR calculator I found on line. Hopefully it will be ok but if not further advice may be necessary. Many thanks for your patience.

 

Regards, Pete

[PeteT]

Hi guys,

 

Another problem (sorry it's all I ever seem to contribute to this forum). Following on from all the above. The liner protrusion is spot on and remains so. However I fitted all the Pistons today and noticed something very odd. When I measured the piston height in relation to the liner I found the measurements to be uneven. For example on number four the back of the piston is .003 below the liner (fine) but the front is .0012 above! The others are all different measurements but have the same problem in that when viewed from the exhaust side of the engine the piston is low at the left but high at the right. The 'deck height measurements I gave above were on one piston which I measured in the middle and seemed ok. The only thing I can think of doing is removing number four and reversing it on the conrod (no split skirt so can be fitted either way) and seeing if the discrepancy reverses. If it does I will be focusing on the Pistons.

 

Apologies again for this seemingly endless saga.

 

Regards, Pete

[Motorsport Mickey]

That's why I specified checking in 4 positions around the circumference.

 

Whether it be liner heights or Piston crowns they can all be incorrect through two planes, hence they need 4 measurements taking to ascertain what the parameters of the measurements are and remove the comfortable feeling you get when you just check one dimension which falls in the centre of the range. Go ahead and reverse one piston to see what happens.

The pistons of course should return the same dimensions piston crown to liner when measured in the plane through the line of the crank and their gudgeon pins. They being immovable objects and fixed parallel in line with another. However the pistons will obviously rock across the block as they hinge and tilt upon the gudgeon pins. Because of the mighty hand of volumetric pressure (the compressing fuel/air mix) the actual attitude of the piston should be neutral equalising the pressure across the piston crown and hence the tilt across the engine will even out, but not any piston to top of liner difference front to rear of the engine, it being fixed by the crankshaft and gudgeon pins attitudes.

So...measure the piston crown to liner in all 4 positions around the circumference, write in permanent marker on top of the pistons +3 -12 whatever. To give more meaningfull figures mimic the top of piston pressure by changing the piston attitude by pressing down with the shaft of a hammer on either side of the piston across the block - they should equalise at a median amount between the top and bottom measurements. If the reversing of the pistons attitude on number 4 also changes the measurements in the same order then given that the crankshaft axis and the deck height of the block is parallel the only other measurement or attitude that can change it is the straightness (or lack of !) of each conrod.

We are assuming that you have new pistons which will be manufactured to a high standard and will easily be within minute amounts difference between them, and the small ends in the conrods have been replaced and honed. That in itself should mean that the axis of the conrod big and small ends would be parallel and therefore the piston crown would lie perfectly even between the front and rear of the engine.

 

Bit of deduction to do before further advice can be given.

 

Mick Richards

[PeteT]

Thanks Mick,

 

I'm looking forward to finding the culprit tomorrow. All your assumptions above, re new little ends etc are correct. Fortunately I have another set of conrods etc if necessary, so it should be straightforward to find the problem. Many thanks for your patience.

 

Regards, Pete

[Rob Salisbury]

Hi Pete, as all 4 have the same problem to a greater or lesser extent, it sounds like, to me, that the small ends have been incorrectly installed or honed such that the gudgeon pins are not parallel with the big end journals, or the rods could all be bent. This all goes to show you can never take too many measurements, though the agricultural heritage of these old lumps means they'll work to a greater or lesser extent however they're flung together!!, this aint Formula 1 after all!!

Keep checking, Cheers Rob

[PeteT]

Hi Mick,Rob,Neil, (and others)

 

Just swoped out the conrod on the worst one (no 4) for a known good one and the figures are radically better. Mick - I rocked the piston as you suggested before I measured the height of the piston in relation to the top of the liner at four points and now it reads:

 

New readings: front +.002 back -.001 top +.001 bottom +.002

Old readings: front +.0012 back -.003 (only measured fore and aft)

 

I checked the conrods on a sheet of glass before I had the little ends done and they looked fine so my conclusion is the little ends have been screwed up.

 

Mick- so turning to deck height, my old gasket is an average thickness of about .0037 and you recommended a total deck height of .0040 ques do I need to take anything off the piston crowns or is that close enough?

 

Regards, Pete

[Motorsport Mickey]

Hi Pete,

 

If it was my engine I would now rebuild with conrods that are the finished article, ie straight and without twist and with little ends replaced which are a gentle thumb press upon the gudgeon pin and which are also parallel to the conrod big end.

 

When the engine is back together again carry out the measuring of the piston crowns in 4 positions, record them and then we can review what the then accurate component fitment give.

 

PS: On your new readings given above

 

"New readings: front +.002 back -.001 top +.001 bottom +.002 " - Does the reference to top and bottom refer to the piston deck heights when measured across the plane of the crank when the piston has been "equalised" upon it's gudgeon pin rotation ?

 

Mick Richards

[PeteT]

Hi Mick,

 

Thanks for your reply. Yes I rocked the piston around the axis point of the gudgeon pin as you sugested and equalised it out. Though the figures are so marginal I'm guessing it's flat. The test conrod I used was known to be straight although the little end is a bit old it was good enough to prove the point. I've returned the con rods to the machinist who installed the bushes and he's busily measuring them as we speak. He said he's never encountered anyone who measures everything like I do, so I'm guessing he's never met you

 

Regards, Pete

[BlueTR3A-5EKT]

Has the machinist done any machine work to the top face of the block or the the liner?

 

If so you are correct to measure all the items as the pistons will be nearer the top of the bores compared to standard.

 

I too struggled when first encountering a block with 0.005" skimmed off it to "clean it up" I then had to have the liners done to get the protrusion correct, then machine the crowns of the pistons to get the deck height right.

 

Once the liner protrusion was correct------

 

First try swapping piston and con rod assy from liner to liner, to see if there is any improvement - Unlikely if the crank has been ground properly.

 

I trial fitted the lot then swapped pistons (not con rods) about to get the deck heights as near equal as possible. There may be a dimensional discrepancy on the pistons.

 

Next step----

 

Onto the lathe to machine off the known dimension needed to get the correct deck height.

 

Or if satisfactory build and enjoy.

 

Bucket of boiling water is useful when doing gudgeon pins.

 

Peter W

 

PS Take lots of photos and keep log of the dimensions.

Edited May 15, 2015 by BlueTR3A-5EKT

[Motorsport Mickey]

Hi Pete,

 

Sadly I've been exposed to many machine shops and realised that the operators are "jobbing" operatives ie: they plonk things on their machine and never give a thought to what they are doing or trying to achieve.

 

These engines are a classic well over engineered design and are relatively easy to get rebuild and get an excellent result as long as you have a relentless attitude to the minutia of how they go together. All parts are easy to machine and measuring the parameters of their dimensions allows you to build engines that will give you 100,000 miles without problems, and how many other 1950s engines will exceed their original HP figures by over 100% and give plenty of excitement at relatively little cost.

 

I read you'd said you'd had the block skimmed and if the pistons are new the compression height (gudgeon pin to piston crown) will likely be within a thou, so when equipped with straight conrods with little and big ends the correct size and parallel to one another, the measuring of the pistons should straight forwardly show an amount broadly similar that can be machined to give you your piston to head clearance. As Peter says boiling water is useful for gudgeon pin manoeuvring.

 

Mick Richards

[PeteT]

Thanks guys,

 

Mick Peter - yes the block was skimmed and .005 taken off the liners. They have been pulled down using the head and old gasket and are pretty much perfect. The conrods and the little ends are now being measured to determine the problem but as the readings consistently put all four piston crowns as slightly tilting backwards my money is on the bushes. When this issue is resolved I will trial build it again and get an accurate measurement of the deck height using Micks method of taking the cylinder head as the reference point. I will report back when I get to that stage to see what the advice is regarding any skimming of the Pistons.

 

Regards, Pete

[PeteT]

Hi guys,

 

Turned out the conrods were bent so have swoped them for another set I have which give better readings. I will give the readings for each piston 'back front top bottom' as before. Hope it still makes sense:

 

Number 1 back minus .002 front 0 top 0 Bottom minus .002

Number 2 back 0. Front +.006. Top 0. Bottom 0

Number 3 all zero

Number 4 back 0. Front +.002. Top 0. Bottom 0

 

Mick/Peter- I'm still in search of the .0040 deck height from liner top to head. Do you think these figures are ok? Do I skim just the Pistons that are high or all of them?

 

Thanks for your time once again

 

Regards, Pete

[Motorsport Mickey]

Hi Pete,

 

Well apart from No2 cylinder which shows a 6 thou lean the other 3 are acceptable, (not if I was rebuilding it as a race engine though you understand). Effectively all the other pistons are within a 2 thou range of zero No1 being -2 and No4 +2 and No3 being recorded as 0 in all planes. A skim on them to achieve the 40 thou deck height will be ok but I'd like to know why No2 has the 6 thou lean.

You say you swapped them for another set you have, are they checked as straight ? and have the little ends been replaced and honed on all ? Also how are you measuring these piston heights ? straight edge and feeler gauges or depth micrometer ? nothing wrong with feeler gauges but repeatable results are easier for most people to get with a depth micrometer.

 

Mick Richards

[PeteT]

Hi Mick,

 

The little ends haven't been replaced yet as I thought I would check the piston heights out first but I intend to replace them. I'm measuring with feeler gauges and a straight edge. I've repeated the measurements on number two and I can confirm the odd lean on this piston. Any thoughts?

 

Regards, Pete