Cp Piston To Bore Clearance And Ring Gapping

[N1GTR]

A tad off topic.... Booked in for a tune in 12 days time. See how she goes

Would love to hear results if you dont mind

[TriniGT]

Okay so should I be worried about the four thou bore the machine shop gave me for piston to wall? He used the pistons when doing the honing. Let me know.

Should I worry?

[proengines]

No. .0005" extra is much better than .0005" too little. The clearance they specify is normally the minimum clearance that will work in the vast majority of situations. In all honesty, most of the cheap bore gauges that people use to check a bore are only accurate to .0005" anyway and depending if the block was allowed to cool before the final honing and measurement they can move that much anyway.

[darren lewis]

Should I worry?

the cp,s will run .004 clearance at the pin if the bore measures right on 86mm exactly. get a competant machine shop to measure the bores , hone the bores correctly and the gaps at what youve stated will work fine. a correct hone finish would be my favor over a tad more piston to bore clearance. we have run the cp,s at .006 thou clearance after a few teardowns and you can hear them at that clearance and dont seem to upset the knock sensor.

[T04GTR]

i used trust/os pistons. at 1.9thou they are fine. but i didnt like the fact that they came with no ring spec sheet. and was told but the trust dealer at the time they are gapped to suit the 1.9thou bore.....

done 50,000km at 1.6 bar no drammas as yet

[ahh 33 s2]

hey guys, so to steal the thread but i am dropping my CPs off tomorrow at the machinist, my mate/ building adviser has not used CPs before. im looking at around 350kw-400kw at rears and spinning to around 8500 tops.

can i get an idea of what a couple of u recomend as far as piston to bore and ring gaps

and how much better is the ACL oil ring over the CP.

[GTRsean]

Mate im a big fan of the ACL's but no bastard wants to use them. The thick upper rings seal really well...even in big clearanced drag race stuff and as you say the oil control is much better than the CP's as even at 16 thou the CP's tend to 'float' on the bore.

Ha, ha I used em (ACL's)!!!

Built mine near the end of last year and have put 10,000k on it so far. Got the block machined to 86.5 and run a 3.5 thou piston to bore clearance, then built the rest up myself.

I was a little generous with the compression ring end gaps 17 top, 21 thou second ring, but it seems to work well.

Dynoed at 363RWKW at 20psi and revs up to 9000RPM. Daily driver since 2004! and still is.

[ahh 33 s2]

any opinions on my application i am tending to go with dirtgarages slightly larger clearnces, meeting the manufactorer in the middle..

as i have said its going tomorrow so an opinion would be great

its in a 26 at 86.5

[TriniGT]

Mate im a big fan of the ACL's but no bastard wants to use them. The thick upper rings seal really well...even in big clearanced drag race stuff and as you say the oil control is much better than the CP's as even at 16 thou the CP's tend to 'float' on the bore.

Whereabouts can I order the ACL rings from and are they piston specific or just bore specific? Meaning do I ask for an 86.5mm set of ACL piston rings? I have no problem spending the extra on them.

Jason.

[marks33]

"All car bitz" in coopers plains I just got a set this week.

[shanef]

quantum engineering in brisbane, they are aactually to suit a mitsubishi engine (forget the code) as you need to match the ring thickness up

[TriniGT]

I started my gapping process only to find out that when I place either the top or second ring in the bore that the gapping is bigger than what was recommended i.e top - 17 thou, second, 19 thou and oil around 16 thou. I am guessing that means that the machinist honed my bores too big allowing the rings to have a bigger gapping. What advice can you'll give me to correct this and please don't tell me to get 86.5mm and rebore? Can I get some ACLs that would fit the build? This has got me really frustrated.

[GT-RZ]

How much bigger?

[TriniGT]

These are the gapping readings I am getting,

Top Ring - 19-20 thou

Second Ring - 25 thou

Oil Ring - 25 thou

Could it be that I got the wrong set of CP rings? The number on the bag says CPN-3386. This is very frustrating.

[GTRNUR]

Back to basics. You need to measure the pistons witha micrometer and see what cylinder bore to piston clearance the block was setup with. Check your piston "recommended clearence" data. It will be between 2.5-4 thou depending on the brand and material of pistons. If thats ok then look at rings. Something not right and to proceed without the propper checks will end up in disaster.

[r33_racer]

Wouldnt you want a steel gas nitrided top ring rather then a chome/moly coated ductile iron top ring?

Or do CP offer a proper top ring now? like acl and mahle use. Out of curiosity, last time we used several sets of CP's they didnt offer a good top ring.

I would do what shane said and get a set of acl rings that have the same thickness about 1.5mm, 1.5mm and 2.7mm from memory???...but I would measure the thickness of your rings now with verniers to see.

Edited July 12, 2009 by r33_racer

[r33_racer]

Sorry for hijacking the thread, but I have a question....

Since most blocks when bored/honed are done with a torque plate(well if done properly)...if you were being precise with your ring gaps, then it would make sense to check and set ring gaps whilst a torque plate is bolted to the block right?

Does anyone do that? or only pedantic builders goto that length? I understand the bore distortion might only be .0005 or thereabouts going from torqued to untorqued.....but still...might only be half a thou, to some thats not much, to others thats alot.

Been thinking about it, and was curious if anyone bothers?

[BOOSTA]

Hey Guys,

I work for the Australian distributor of CP Pistons...

If anyone has any questions about CP Pistons.... let me know and i'll do my best to answer them!

Cheers Peter

[proengines]

Sorry for hijacking the thread, but I have a question....

Since most blocks when bored/honed are done with a torque plate(well if done properly)...if you were being precise with your ring gaps, then it would make sense to check and set ring gaps whilst a torque plate is bolted to the block right?

Does anyone do that? or only pedantic builders goto that length? I understand the bore distortion might only be .0005 or thereabouts going from torqued to untorqued.....but still...might only be half a thou, to some thats not much, to others thats alot.

Been thinking about it, and was curious if anyone bothers?

I've done it both ways on an RB and the difference is negligible plus its awkward to square the ring properly with the torque plate fitted as it's only slightly larger than the bore size.

[r33_racer]

appreciate the response mate. did you manage to get those pics of the rd28? or too busy? no issue if not.

Have you ever checked bore with and without torque plate to see what variation there is?