Piston Rings and Sizing

[AarhusTr6]

Hi all

I made some posts before on burning oil and seeing a light blue haze, especially on hard deceleration and given some good suggestions, but overall feeling was ring/piston/bore.  So I start my winter work and here are some basic facts of where I am:

• Complete top end rebuild and head rebuilt by a well know UK based professional 2 years ago
• Fitted lovely, still burning oil though....
• For this Winter, I have removed head, and sump, one piston out, by pushing from underneath.  Also big ends etc all look really good.
• Despite some recommendations to lift engine, prefer to keep in situ, limited space is main issue

Piston etc all looks OK (not that I am really an expert in any way), but I am confusing myself on what to do next....

 

• I do not have any measurement tools, less for a cheap digital gauge.  But will buy what's needed, but I am not a rich man!
• Was thinking of removing a ring from a piston and measuring ring to bore wall gap - - not totally sure of what to then do with results...
• Was also thinking of measuring the bore and thinking results may show some data on if bore is worn or not
• Was also thinking of over-sized piston rings, but guess I need to address bullets 2/3 to decide on what to buy - or do next

Much looking forward to some good practical help

Richard in Denmark - in a cold small garage

Edited November 18, 2022 by AarhusTr6

[Andy Moltu]

Remove the rings from the pistons.

Select one and push it into the cylinder bore - push down using the piston to make sure it is sitting "square" in the bore and measure the gap with feeler gauges.

Do this top, middle and bottom of the swept part of each bore and compare the gaps using the same ring. If the gaps are similar and the bores are no major marks on the bores then you will likely get away with a hone and a re-ring to the size of piston fitted (std, +20 or whatever). (If the gaps vary then the bores are warn and you'll need to rebore.) Assuming there isn't too much wear, check the gaps with one of the new rings to be sure that gap isn't too large. (If the new ring gaps are small, make sure you have really honed it aggressively enough to have removed the glaze.)

If you need over sized piston rings you would be better off re-boring.

[Motorsport Mickey]

Don’t bother removing piston ring and measuring the ring gap ( between ends) when placed inside the bore. As long as it has a minimum gap of 15 thou ( to prevent the ring ends from butting against each other) unless you know what gap they started from ( I’ve run them at 30 thou before, it doesn’t give measurable blow through) it doesn’t tell you whether the ring or bore is worn.

Buy a cheap outside micrometer from e bay to cover your bore range £15 ? And a set of telescopic gauges ( often called snap gauges( it’s the noise they make when undone) used, …I’ve seen at £30. Use the telescopic gauge inside the cylinder bore opening them until they are slightly bigger and then rotate them through horizontal with the handle vertical. They will open and self centre then lock off just after their tightest feel, with the knurled end knob, do this 3 times and use the centre reading. You’ll get better with them as you get practiced, then measure the open tele gauge using the centre reading as said with the micrometre. You’ll be within 1 thou and as you use more often you’ll be able to measure within the 1 thou to judge 1/10s of thou. Measure the bore at 1” from the top, and then the centre and then about 1” from the bottom where it is likely to be your original bore. Write the dimensions down.

Then using the same micrometre measure around the dia of your pistons for the largest dia ( they aren’t made round) make at least 4 measurements in a cross pattern. I normally reckon on these Dias you’ll need a minimum 3 1/2 thou clearance piston to bore (new) but they’ll run up to 5 thou before you need to be replacing. Depending upon what you get, a piston re ring set might sort the job. Report back for more confusing info.

Mick Richards

Edited November 18, 2022 by Motorsport Mickey

[harlequin]

Richard 

When you get your new rings go for Hastings and avoid Grant. The Grant have a small tag on the ends of the corrugated oil ring which are hard to get fitted correctly and have been known to break of completely. 

They are probably OK if you are a professional and are fitting them everyday but why take the risk

George 

[BlueTR3A-5EKT]

Deglaze the bores?

[ntc]

46 minutes ago, BlueTR3A-5EKT said:

Deglaze the bores?

+1 ie hone you need new pistons and rings as the gap in the ring groves are to wide , and the pistons have side ware rubbing the bore.

[AarhusTr6]

Hi all

 

thanks for help.   Can anyone advise a bit on de glazing?   Is that the big wire thing you out on the end of the drill ?

Richard 

[BlueTR3A-5EKT]

28 minutes ago, AarhusTr6 said:

Hi all

 

thanks for help.   Can anyone advise a bit on de glazing?   Is that the big wire thing you out on the end of the drill ?

Richard 

You probably mean a Flex-hone   Looks like a muddy hedgehog on a stick.   Not cheap but very effective.

You will need to wash out the grit after use or fully protect the crankcase when using with lots of rag.

Some would just rub the bore face with glass abrasive paper to remove the glaze.

 

 

 

 

Edited November 20, 2022 by BlueTR3A-5EKT

[poolboy]

Please wait while image is uploading...

Please wait while image is uploading...

I've used the flexhone...good results but there is a technique that should be followed...

http://www.brushresearch.com/flex-hone-instructions.php

Edited November 21, 2022 by poolboy

[poolboy]

Flexhoned

[Nigel Triumph]

I'm also a fan of the Flexhone, used it successfully on a Triumph 6 pot and Ford Essex V6. It can be used in situ but take great care to protect engine internals especially the crank journals. Clean up scrupulously afterwards,  as oil mixed with abrasive gets everywhere. 

Nigel

[Schnippel]

Hello Richard,
a very typical picture. Your machine once had a rust problem!
The rings then wear out disproportionately.
Also check the height clearance in the piston groove of all rings.
I think there are clear marks in the cylinder barrel.
You can take pictures and show us then we can decide whether big or small intervened. I could lend you Flexhone

Picture shows refresh with flexhone

Everything will be fine
Ralph

[Motorsport Mickey]

31 minutes ago, Nigel Triumph said:

I'm also a fan of the Flexhone, used it successfully on a Triumph 6 pot and Ford Essex V6. It can be used in situ but take great care to protect engine internals especially the crank journals. Clean up scrupulously afterwards,  as oil mixed with abrasive gets everywhere. 

Nigel

Clingfilm is your friend, it wraps easily around the crank and self adheres. Build it up in a couple or more layers and you can wipe it off easily to get rid of the detritus from the honing which falls down the bores, then strip it off the crank and bearing housings leaving it squeaky clean. Before you remove the cling film wash the bores with paraffin and paper towel, if it comes out grey you still have ground metal on the walls, continue until a clean paper towel rubbed on the walls comes out unmarked. Honed engines in situ like this a number of times...easy peasy.

Mick Richards

[Schnippel]

Hello,

Perfect ......... that's exactly how I do it too.
Because that's how I learned it at DB.

Ralph

[Motorsport Mickey]

4 hours ago, Schnippel said:

Hello,

Perfect ......... that's exactly how I do it too.
Because that's how I learned it at DB.

Ralph

Amazing ...even Deutsche Bank has it's fingers in good engineering practice ! Lol

Mick Richards

[Waldi]

Is there a difference between the ball-type and the 3-arm type honing tool? I used the 3-arm type with good results.

Waldi

[John L]

The main problem insitu is getting the bores clean, or your new rings will last only a day!  As Mick says white paper has to come out white, you will be amazed just how much wiping you have to do to get it clean.

John

[Rob Salisbury]

Hi Richard,

                 Really before you go down the glazebusting route, you have to follow Mickey's advice and measure the piston to bore clearance, if it exceeds 5 thou. then any success with honing will be short lived, .... as a quick, unscientific check put the piston back in its correct orientation and at the top of the cylinder bore. then see if you can slide a 5 thou. feeler gauge down the piston skirt just below where the score marks are, if you can then you either need new pistons or (preferably) a rebore, make sure whoever does the rebore has the new pistons so that the correct clearance is achieved.

In many ways pistons are just there to fill a big hole and keep the rings in position, it's the rings that do the sealing and if the piston can wobble around and bang into the cylinder walls (the scoring on your piston), then the rings will never seal properly.

Cheers Rob

[Motorsport Mickey]

Here you go Richard, try this article, it's how I've approached pistons/Rings/liner bores over the last 30 years. As Rob says all the pistons do is carry the sealing agent (rings) up and down the bores, the hocus pocus of various ring systems are debunked by an engineer especially as regards ring gaps, doesn't matter if they are staggered or in line and hardly matters if the piston ring gaps are large, just don't get them tighter than 15 thou.

Piston Ring gaps.

This article from the Institution of Diagnostic Engineers (first published 1995) may give you food for thought, and it's how I've approached piston ring fitment through the years.



Ring Gaps vs Knowledge Gaps

Frequently I hear in court that when an engine is dismantled it is discovered that the ring gaps were not staggered when they were installed. Frequently I read workshop manuals that go into great detail on the necessity to stagger ring gaps. Frequently these manuals specify ring gap limits – which is yet another myth we can bin before we are finished.

Piston rings are free agents and can rotate or not rotate as they see fit. They are not in touch with the base of the groove and neither are they trapped between the upper and lower faces of the groove. The rings are entirely free to rotate – except where a stop peg is fitted – so what's the point in staggering the gaps on installation?

We used to work on a minimum of 0.020" back clearance on radius or, to put it another way, the inside diameter of the ring when installed in the cylinder must be at least 0.040" bigger than the groove root diameter. Minimum side clearance was generally held to be 0.0015" and if you could fit a 0.006" feeler gauge in the groove along with the new ring then the groove was "goosed" so the piston was replaced.

The piston ring was manufactured with a tangential load – the force with which the ring presses against the cylinder wall – but apart from that it is completely uncontrolled. There is no way, under these circumstances, that you could prevent the ring from turning so, to repeat the question, why stagger the ring gaps on installation?

Equally mislead are those who expect ring gaps to stay staggered when the engine is in operation. When there is clearly nothing to prevent the ring from rotating, why should the gaps stay staggered?

More than one county court judge has fallen for the hocus pocus that because the gaps were in line when the engine was dismantled, they must have been in line when installed. Absolute poppycock! Yet the inclusion of such rubbish in workshop manuals does admittedly give it an air of authority.

When you think about it, you don't need me to tell you – but I will anyhow – that rings do rotate in operation. Every now and again the gaps do line up – and once lined up there is a tendency for them to stay lined up at least until the vehicle hits the next pothole in the road when one or other will rotate and break the line. Staggering ring gaps when installing rings is a myth that we can bin forthwith.

Even worse is the preoccupation with the size of the ring gap. Yes, there is a minimum but this varies considerably depending on the material used. Normally 0.003"/0.004" per inch of bore size is given but where, for example, low expansion SG (spheroidal graphite) iron is used, it can be considerably less, so what about rings with gaps that are too big.

Well, the answer to that was that you melted them down and started afresh – until AE research asked the question, "What is too big?" and set out to quantify that. The results were interesting – very interesting – and what you are about to read was kept quiet because it bestowed an enormous commercial advantage on AE. This is probably the first time the information has been published although the research was undertaken in the late 1970's – almost 25 years ago.

A Ford Kent engine was stripped and fitted with compression rings which had end gaps of 0.015" when fitted in the bores. The engine was wired up with the usual telemetry to measure blow-by and oil consumption and then run in one of the test cells. After making due note of the blow-by and oil consumption, the engine was stripped and fitted with new compression rings with gaps of 0.025" and the test cycle repeated.

These rings were subsequently replaced by ones having end gaps of 0.035" and the test cycle repeated again. It had been planned to stop at 0.035" gaps ----------> but the results were so interesting that it was agreed to proceed to 0.045” and then not to 0.0055” but to 0.0625” – 1/16"!

Whoever heard of rings with 1/16” gaps – a ridiculous figure – but the interesting thing was that the increase in blow-by and oil consumption at 0.0625” was only marginally above the figures obtained with 0.015” gaps.

Practical tests established that the gap was not the villain of the peace. To all practical purposes the size of the gap didn’t matter. It is important to stress at this point that we were dealing with compression rings that were brand new when fitted to the test engine.

The gap was specially manufactured for the tests. So how come all oil burners and heavy breathers have ring gaps you can back a bus through? Well, the tangential load that the ring exerts onto the cylinder wall is a direct function of its radial thickness.

As the periphery wears in contact with the bore, the radial thickness obviously decreases, as does the tangential load. Peripheral wear means a smaller ring o/d and this manifests itself as an increase in the ring gap, it's not the gap but the reduced tangential load that is detrimental to the performance of the engine. The ring gap is a complete red herring.

Imagine four top compression rings all with 1/16” gaps. The total gap for all four would be 1/4”. Now imagine the seal provided in an 80 mm diameter bore. Pi x Diameter = Circumference, so we have 3.14” x 3.15” = 9.891”. Multiply that by four cylinders and we have 39.564” – over a yard of contact seal between piston rings and bore. Now visualise the many litres of blow-by and consider whether all the gas is squeezing through 1/4” of total gaps or passing through 39½” of reduced pressure contact seal!

But even this ignores one important facet of the argument because there is not just the one compression ring on a piston – there are usually at least two and that is because rings work as a team to form a labyrinth seal.

For gaps to be the villain of the peace, the gas would have to find the gap in the top compression ring and pass through. It would then have to circulate to find the gap in the second ring and pass through that and so on. Now this may be possible if the power stroke lasts for 10 minutes but it doesn't, does it?

At 3,000 rpm the power stroke duration is a mere 1/100second. Quite simply, the power stroke does not last long enough for the combustion gas to find its way around the maze – or labyrinth seal, so the villain of the peace has to be the reduced tangential load of the ring on the bore caused by peripheral wear or reduced radial thickness of the ring.

This was our hypothesis based on the results obtained in the engine test cell but it took a very clever American to prove it. This genius invented telemetry that measured gas pressure between the piston rings in a working engine.

Use of his brainchild revealed that some gas did get through the top ring gap sufficient to generate a hell of a pressure between the top and second rings – so it clearly was not finding the gap in the second ring. The labyrinth was working well. Caterpillar and IHC must have thought it was working too well because they increased some second ring gaps to 0.050” and 0.070” thought to be beneficial.

Come to think of it, the exception proves the rule – as usual. Two stroke engines would not need stop pegs to prevent the end gap from crossing a port if the ring didn't rotate. The people who allege that ring gaps were not staggered when installed just because they are in line when the engine is dismantled don't need stop pegs.

The very presence of a stop peg also proves my point about the size of ring gaps. Where a peg is fitted, the end gap has got to be 1/8” to accommodate the peg. There would be one hell of a draught through that if the 0.015”/0.018” boys were correct.

This knowledge was commercial dynamite because, instead of the '0.015”/0.018” spec., it meant that new rings with gaps over 0.018” could be used without any detriment to the engine's performance. The gap was only detrimental when it was the result of peripheral wear. Customer acceptance was the only problem.

To re-educate the customer would let the cat out of the bag, thereby losing the distinct commercial advantage. It was decided, therefore, to accept rings with gaps of up to 0.030” in a nominal bore but even then there were arguments. 0.030" in a nominal bore is 0.045” in a bore worn by 0.005” – and it's normally engines with this sort of wear that get new rings.

It made diagnostics a lot harder too because when all rings set off in the 0.015”/0.018” area gaps of .040” meant something but now, when you don't know what they set off at, what they measure is meaningless.
Well, now you know. All rings are free agents to rotate as they like, making staggering of gaps on installation a joke and ring gaps are not a problem provided that the gap is not the manifestation of reduced ring radial thickness caused by peripheral wear.

M H Booth F.I.Diag.E


Interesting eh... for what it's worth I always fit my Piston rings staggered it just makes me feel better, having confirmation that it doesn't matter a damn is just insurance...I can't possibly get it wrong !

As for Piston ring wear as stated in these posts previously it could only be estimated by confirmation that the bores were in a good condition in the first place and the piston rings had been accurately gapped. Where this information is not known measuring the piston (remember they are not round) and the cylinder dimensions will show how worn the cylinder is in comparison, remembering that on Pistons up to these sizes wear up to as much as .005 or .006 is allowable. (Complete Automotive Engine Rebuilding by Robert Scharff ) If you get up to this wear then resizing of the pistons and bores are the way forward.
 

Mick Richards

Edited November 21, 2022 by Motorsport Mickey

[poolboy]

MIck's post about BMEP might be useful for breaking in those new rings, too.

https://www.tr-register.co.uk/forums/index.php?/topic/50484-cylinder-bore-wear/&do=findComment&comment=410396

 

Edited November 22, 2022 by poolboy

[john.r.davies]

Indeed, rings rotate at about one thousandth of the rpm, but in random directions and speeds.  So staggering is pointless.

And, as occasionally they will line up, no one suggests that this as a cause of intermittent power drop.   

John

[John Reilly]

I found this thread very interesting, looking at the flex-hone tool supplier, I see there are variables for honing as well as selecting the diameter, what would be the correct abrasive and grit for the TR engines?

When I restored my TR3 engine I fitted new liner, piston & ring-set kit. Should I have been more selective in the choice of piston rings? I see from the previous that Grant and Hastings (albeit for a TR6 I think) merits were mentioned......? What does the small tag on the end mentioned look like?

Curious

John

[poolboy]

3 1/4  inch diameter flex hone 240 grit gave the result in the picture I posted

You should get 3 1/2" a cylinder wash brush as well

Grant ring tabs,,the picture is blurry but the red tab must remain  butted against the green one...not overlapped.....Hastings were my choice