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Bad leakdown test, scratched cylinder walls

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Hi guys! Before i pulled my head out i made leakdown test. It was 20 percent in all cylinders. Test was done on COLD engine! What do you think abou these numbers? I think that it is bad on engine that has 2000 miles. There was very little oil consumption. And pictures of scratches on cylinder walls are attached. The scores can be very hard feeled by nails.

What do you think, it is ok and i can run it? Do rehone and put new rings? I have CP piston 88mm and 300HP NA engine - what is your recommended p2w clearance? Now i have 0.003" and i dont know what rehone do with clearance and possible piston slap.

Thank you.


Attached Files

With the exception of the 3rd photo you've attached, most of that looks like fairly typical wear in the bores coupled potentially with some amount of debris that's made its way through the engine. I'd pick that the scratching visible in the other 3 photos probably would be hard to feel with your fingernail. The 3rd photo looks worse though.

I've found that leak down testers can vary in their readings so I wouldn't necessarily be worried about 20% on some testers. Where is the leakage occurring though? Past the rings or past the valves? If you have the engine apart then a light hone and a new set of rings probably isn't a bad idea. 0.003" is probably adequate for a N/A engine but it wouldn't hurt to increase this to 0.0035 or 0.004". Much more than this is likely to result in noise when the engine is cold.

Thank you Andre. Leakage is past the rings. So bigger P2W is not problem? P2W 0.0045 is right for high HP NA car or is time to buy bigger pistons? Do you have experience with cold vs hot leakdown test and differences in measurement? Thank you.

Leakage past the rings doesn't mean that you've got excessive P2W clearance - It's the ring seal that results in this sort of leakage. Now P2W can affect this since the correct clearance is important to stabilise the piston in the bore and help ensure ring seal, but this won't affect the leak down test that's performed in static conditions. A clearance of 0.0045" isn't what I'd call excessive but it's certainly more than you'd need for a 2618 forged piston in an N/A engine. If you're at 0.003" right now though you should be able to clean up the bores with a light hone without resulting in excessive P2W.

Generally you can expect a cold leak down to show higher leakage than a hot leak down, much like a compression test. The true value of the test is tracking historical data on your engine from new, performed under the same test conditions.

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