Piston Ring Questions

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Alexis
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Piston Ring Questions

Post by Alexis »

2 questions really...

I have a set of CP pistons and they have supplied me with a top, 2nd and oil scrapper rings, but you need to set the gap correctly due to the application. How do you go about doing this? File ever so slightly on the end of one of the rings? Then how do you measure the correct clearance of the ring?

Other question is i have total seal rings for the 2nd ring, again i presuming this again needs a certain clearance, but the main question is, how do you go about installing them? :lol: Do you put the first ring on, then the other ring and try and get them to press together?
Alexis
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Joined: June 22nd, 2006, 9:06 pm
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Post by Alexis »

Ok, figured out i was being a bit silly with measuring the gap clearance on the piston rings (google came to the rescue), so if anyone else needs to check gap clearance, piston rings are put into the block, then measure the gap bewteen the ring. Also read that you should check the clearance at the top of the block as well as the bottom of the block due to the way the block can taper?

Although still none the wiser on how to fit the 'total-seal' rings
Guy Croft
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Post by Guy Croft »

Alexis, sorry just pressed for time, I will reply..

GC
Alexis
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Post by Alexis »

No problems Guy, i'm not actually fitting the rings just yet, so can hold off for the time being if need be :)
Guy Croft
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Post by Guy Croft »

Re:
Ring fitting with his Fiat Coupe 16v Turbo Alexis wrote:


…œI have a set of CP pistons and they have supplied me with a top, 2nd and oil scraper rings, but you need to set the gap correctly due to the application. How do you go about doing this? File ever so slightly on the end of one of the rings? Then how do you measure the correct clearance of the ring? Other question is I have total seal rings for the 2nd ring, again I presuming this again needs a certain clearance, but the main question is, how do you go about installing them? Do you put the first ring on, then the other ring and try and get them to press together? Ok, figured out (Google came to the rescue), so if anyone else needs to check gap clearance, piston rings are put into the block, then measure the gap between the rings. Also read that you should check the clearance at the top of the block as well as the bottom of the block due to the way the block can taper? Although still none the wiser on how to fit the 'total-seal' rings‚



OK - First we need to be absolutely clear about the type of ring pack. As I understand:

Top: You have a CP lightweight racing top ring, conventional style rectangular, possibly molybdenum inlay or chrome faced/plated made from ductile iron or plasma nitrided steel and possibly carrying an etched mark or dot to indicate the top face of the ring. (Markings always go uppermost ie: toward cylinder head)

2nd: The second ring is a 2 piece Total Seal ring consisting of coated steel machined ring and associated steel sealing rail.

3rd: The third ring is what type? A 3 piece ¢‚¬Å“ 2 rings and expander rail?

Please also tell me what you found by way of ring end to end clearance when you offered them to bores.

You can safely assume that the rings for each piston are the same, but you need to check one top ring and the machined TS second ring (not the rail), plus the rings of 3rd ring (not the expander). It is important to make sure that the ring sits perpendicular to the bore axis, turn a piston upside down and use it to push the ring in about ‚½‚.
For ring end clearance you want 14-16 thou (thousandths of an inch, 1 …œ = 25.4mm) ring end clearance on top and second and more is allowable on 3 piece expander type 3rd rings ¢‚¬Å“ as much as 25 thou is OK.

The ring end gaps are measured by aligning them in the bore one at a time and slipping a feeler gauge between them. This in itself is not easy. Rings are very easily damaged/snapped.

If the rings look like they will butt together hard in the bores don¢ž¢t force them.
Overlap one on the other and mark with a very sharp scribe on one ring the excess material to come off. If a lot has to come off I start on the grinding wheel (nicely dressed for the job, I add) and then do a first check, then I clamp a fine sharp parallel file in the vice and work the ring up and down for the next bit, then final stoning with a fine small carborundun stone or fine carborundun / aluminium-oxide tape wrapped round the file. Sometimes you have to adjust the entire pack and this should take the best part of 4-5hrs done carefully. Take the material just off one end of the ring only each time you adjust. Keep the ends square to each other. Each time you adjust the ring length you must dress the corners or you will scratch the bore to bits. How much can you grind or file off, well I have got away with 1mm.

If the rings, as-supplied for your bores, are loose ¢‚¬Å“ they are wrong and you should not use them, though I have to say that you could get away with top ring say 18-20 thou end gap and take a chance on blowby, won¢ž¢t hurt the power on a turbo unit overmuch, some say it¢ž¢s a good thing (I don¢ž¢t agree) but the breather will be working overtime and they won¢ž¢t last as long because they are already oversize. By 22-25 thou end gap (in the worn state) they are ‹Å“worn out¢ž¢. The TS ring, well, they are supposed to be fitted with the gap I have described, but, hey, they are a Total Seal ring so more forgiving about being ‹Å“looser¢ž¢ than they should be.

As far as taper is concerned the bores sizes should have been certified correct by the machining firm if it was rebored, if it is an old bore honed up that is another matter. A well bored and honed block should show no more than 0.01mm (3/10 thou‚) deviance on diameter top to bottom measured with a bore gauge. In fact this is about the limit of calibration of most peoples¢ž¢ bore gauges, unless they have a very expensive electronic one.
It is not necessary to check the rings at any particular section of the bores if it has been rebored and honed. It is vital that the bores are correctly honed for the composition of the top ring and detergent cleaned prior to build.

When putting the ring son the pistons the 3rd ring pack goes on first, then the second and the top last.

More about that when I know precisely what rings you have there.

I hope this is helpful.

GC
Attachments
using a Mitutoyo bore gauge to measure - a rod bore in this case, rod from Simon Bray's GC Vx unit. Lousy photo, it happens sometimes, sorry.
using a Mitutoyo bore gauge to measure - a rod bore in this case, rod from Simon Bray's GC Vx unit. Lousy photo, it happens sometimes, sorry.
SB rod measure D R.jpg (34.34 KiB) Viewed 6667 times
Lightweight 1st, 2nd rings, 3 piece 3rd ring. Thorsten Scheffner's GC race piston (Lancia MonteCarlo Fast Road ) - two thin rings with expander rail between. This is the low turning-torque unit at: http://guy-croft.com/viewtopic.php?t=57
Lightweight 1st, 2nd rings, 3 piece 3rd ring. Thorsten Scheffner's GC race piston (Lancia MonteCarlo Fast Road ) - two thin rings with expander rail between. This is the low turning-torque unit at: http://guy-croft.com/viewtopic.php?t=57
TS forged piston closeup.JPG (13.79 KiB) Viewed 6666 times
Alexis
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Joined: June 22nd, 2006, 9:06 pm
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Post by Alexis »

Guy

That is fantastic and really appreciated :D

I can not confirm exactly what the rings that i have are, put will get some photo's this weekend and post them up, so hopefully can understand what rings i do have.

The oil control ring (3rd ring) as you said is correct, 2 rings and the expander rail.

As for the engine used for this. This was bought 2nd hand after a cambelt had snapped, this was stripped down by myself and given to Serdi UK in Uxbridge along with one of the pistons and the spec sheet that was included with the piston to give them the correct clearance for flex-honing the block.

Hope this info helps in the mean time.

Alexis
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