Forum » General Engine Building Discussion » 2JZ CP PISTON 86.5MM RING NOT FILE AT ALL


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Hi, i recently build a 2jz with cp piston 8.5:1 86,5 mm, and when i went to check the ring gaps to cylinder wall, after some measurement i'll notice that the first and second ring were in standard size with the road size gap on cp piston datasheet.

the engine has only one start up to check if it crank, but never tested on road or at standard temperature.

my question is this:

is it possible to have perfect size ring gap without filing at all?

there's a mistake in boring work at machine shop?

Should I disassemble all to check another time in order to avoid critical engine failure when it will work at standard temperature?


Possible, but did you check the bore on assembly?


- The critical issue is if the gap is too small and when brought up to operating temperature the ring expand to the point where the ends butt up against each other, preventing further expansion - well, except outwards which forces them hard into the bore where two things happen - the oil film is broken down and friction increases the ring temperature massively in an instant, basically seizing the piston and then lots of bad things happen as the connecting rod cries "Freedom" and make an escape attempt out of the engine.

- If the gap is greater than the critical range, the ring cannot heat and expand to the point where the ends butt. there will be a fractionally greater amount of ring leakage through the gap but as it's only a few thou', it is negligible in real terms.

You're looking at the second, which is relatively good.

Today's manufacturing is VERY good. Even for high-volume parts the tolerances are very good. And for parts intended for high-performance use -- I would expect them to be near perfect.

So, not surprised. Still worth checking when installing.

Relax. Don't worry. Have Fun!

Thanks a lot @David Ferguson , I checked the rings before install, first and second ring match perfectly to the specs in the cp piston table, so i'll need only to bolt on last part on my 2jz and see if all works correctly.

I'll let you know if it will be all ok at first official start.