Rootie524

iTrader: (2)

i have a b16a2 block bored to 81.5mm. cp pistons. i had it bored by a guy thats been in the business for over 40+ years. and im using CP piston rings.

i followed all the calculations to find out what my gap should be. first ring should be .017, and second should be around .023. (fored induction setup)

all was going well. pistons one and two were small and i filed them to where they should be. all was well. then i come to cyl three and i put the top ring in to see where im at, put the .017 feeler gauge in there and it goes right in the gap and there is enough room to move it side to side. so after some measuring it turns out the gap before i even touched it in that bore was around .025. the second ring was around .033.

i put those same rings in another bore and they are normal size starting at around .015 and .021.

what the hell happened? it seems like cyl 3 is way over bore. first question is, will this cause a problem? second question is, should i just go out and buy a single piston ring set for say a 82-82.5 mm bore? and go from there? seems this cyl needs oversized rings.

IN VTEC

iTrader: (3)

I'd try the same ring in another cylinder. If the ring end gap comes out smaller, then measure the cylinder bore diameters and see if cylinder 3 is larger than the others.

Rootie524

iTrader: (2)

it must be because i did move the same rings to different cyls and they came out the same. so for some reason cyl 3 is larger..but i have all 81.5mm pistons and the piston isnt loose or anything in that cyl.

very weird.

SAXON

you dont want to use that, if i were you id go get another block and have your machinist pay for it

Gunmetal_B20_Hatch

iTrader: (9)

You'd better give your machinist buddy a phone call ASAP.

IMO, i'd run the ring gap a bit more loose than .017. I gapped mine at .023 and .027 for top & bottom. I plan on making close to 600whp though... IDK how much power youre looking to make. Just understand that its usually better to err on the side of too larger than too small. If the ends of those rings touch after the engine gets into boost a few times then its bad news for the cyl walls and ringlands.

Rootie524

iTrader: (2)

that's very true. i think i got measurements of .025 and .032 on the screwed up cyl. you think i could gap the other ones a little larger and just let this screw up go? or is that too large of a gap?

SAXON

way too large of a gap, unless you go 82mm its not worth trying 81.5

Rootie524

iTrader: (2)

i just ordered a single set of cp piston rings 82mm. that should put me at the gap i need.

I'm just baffled because the piston fits the bore beautifully. no drag or anything. but for some reason the rings just come up too small in that bore. oh well, these rings should put me where i need to be.

Gunmetal_B20_Hatch

iTrader: (9)

your PTW clearance on #3 are going to be different even after gapping the 82mm rings... might want to check that out. You may end up with "piston slap"

V-SPEC 1

You probably would end up w/ bad oil consumption.

SAXON

do not do this, just because the ring gap will be fine does not mean your p2w clearances will be

Rootie524

iTrader: (2)

well the machinist took the used CP pistons that were in it and reconditioned them.

the skirts were all scratched up from the circulated metal particles from the spun bearing. what he did was smooth the skirts down and put a nurl on both sides to bring the metal on the skirt out some to match the bore precisely.

he took each individual piston and matched it to a specific bore than numbered them. each piston fits its bore just like brand new pistons would.

every piston fits great. no excessive drag, and no wobble. so I am not too worried about ptw clearance.

yes, i know there may be some doubters because it's possible hes the one that messed up the cyl 3 bore. but i was there for most of this process because he was showing me how it was done. and it all seemed like it was done by the book and fit correctly.

SAXON

it cant be correct if the rings dont gap out properly (since you tried a couple sets of rings in that cylinder and others)

you dont want to cheap out while you have it all apart

Rootie524

iTrader: (2)

yeah but what im saying is sure he may have ****ed up and overbored that cyl by a miniscule amount. but when he went though and nurled the pistons and matched them to each bore. he did it in such a way to compensate for the overbore. he musta nurled the #3 piston moreso than the others so it fit correctly. sure gap is still off, but the 82mm rings should fix that.

im not trying to be a naive ***** but it seems right. but i will definitely be micing it all out to double check.

but that is my theory:
1. accidental over bore
2. oh **** i screwed up #3 bore
3. ill nurl the pistons to match the bore
4. now i need to nurl the #3 piston more than the others to compensate for the bore screw up
5. ok, it fits fine now but his gap will be screwed up
6. oh well, he will figure it out
7. heres your stuff, thanks for the business

Gunmetal_B20_Hatch

iTrader: (9)

Hope all works out for you!

Never heard of knurling the piston skirt though... Learn something new everyday.

Rootie524

iTrader: (2)

yeah man thanks. i hope it does too. i never heard of it either. he says its something they used to do back in the day but you dont see it much anymore because of how cheap pistons usually are just to replace. but i mean cp pistons are like 500 ish for the set and he told me this is a great a effective alternative for reusing pistons.

im just trying to get this car running and get back to the 450whp it had before it broke. after its running fine ill be going all out in a all forged/sleeved build so im trying to save money where i can. hopefully it wont come back to bite me in the ***, but i have high hopes.