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Scratched pistons and cylinder wall

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Hi Guys! I have rebuilded engine with custom made CP pistons. Honda H22 with stroker 95mm NA 270HP. Run 5000km.

Engine was fine, no oil consumption, good leakdown test. Im going to turbo so that was the reason to put head off.

All pistons are as new. Some scoring on walls, but nothing wrong. BUT on cylinder 2 on exhaust side a found bad scratches :-(

All clearances are fine within specs. P2W is 0.0035 inches. I everything rechecked when looking for couse of scoring.

What could cause this? Debris? Detonation? Bad clocked rings?

Photos looks worse then reality.

Thank you!

Attached Files

Have to mention that block is sleeved with Dartons.

My thoughts, and I would encourage checking with others as they may have specific experience of the same problem. For example - https://honda-tech.com/forums/forced-induction-16/piston-cylinder-wall-clearance-darton-sleeved-block-3123877/

What was the specified clearance for the actual piston and it's alloy used? That looks like it has a momentary seizure, or loss of clearance, not enough to seize entirely, but enough for material transfer. If you're considering using those pistons under forced induction (I'd replace the marked one), then opening the clearance up a little may be a wise move, as the pistons will be absorbing more heat.

If the engine was driven briskly from a very cold start, the relative expansion rates may have caused the piston to heat up fast enough to 'catch up' with the liners, which would be heating up and expanding much more slowly. I recall this being a problem with some seizures of the very early Honda in-line motorcycle engines. In the link at the start they suggest the DARTON's have a slighly lower thermal expansion co-efficient, so a little more clearance may be warranted - there is also mention of the piston expansion with temperature, specifically 30C being mentioned, and I would remind you that the skirt, where the clearance is measured, is much cooler running than the crown which has a much greater bore clearance - and so the expansion along the piston is going to be different.

I would expect a LIGHT hone will clean the mark up as it's a rub mark, rather than actual material removal.

It doesn't look like debris, and I would expect that to show more on the lands, anyway.

Detonation normally affects the top of the piston and with a NA engine is very unlikely to collapse a alnd and pinch a ring - and that would also be restricted to the top of the piston.

Ring 'clocking' isn't something I ever concern myself with (I know that's sacriligous to some ;-) ), as in use the rings are in constant rotation at different rates, anyway, some at times lining up and at other times opposite each other. Again, not something I would expect to cause any damage like that.

Oh, that looked like a lot of carbon for a limited mileage...?

Thank you. Alloy is 2618. Looks rich for you? I think that scratches are from debris. Hope to rehone will fix that. How far i can go with p2w please?

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