<![CDATA[M20 scratched cylinder]]>Replacing a piston that was damage (likely due to running lean) found this vertical scratch in the cylinder wall. I know it's not ideal, but interested in others thoughts. We have already honed the cylinder, I wouldn't say a fingernail catches but you can feel it.a8c31925caba488873f52c96e6d56df9.jpg

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]]>https://wibimmers.com/topic/4889/m20-scratched-cylinderRSS for NodeWed, 16 Sep 2026 06:27:41 GMTSat, 17 Jun 2017 16:26:48 GMT60<![CDATA[Reply to M20 scratched cylinder on Sat, 17 Jun 2017 21:10:16 GMT]]>The "rule of thumb" my engine builder used was bore x .005 for upper compression ring and bore x .0055 for the lower compression ring which resulted in a cringeworthily small .016" and .018" gaps.

First of all use a piece of broken ring to make sure you clean all the carbon out of the grooves thoroughly.

Very important

The stock ring end gap for a stock non-boosted engine is

.012"-.020" upper

and .012"-.020" lower.

Some boosted V8 guys run .025" upper and lower gaps. The ring manufacturers will have some guidance as well

Personally I would go 020" upper and .022 lower at minimum. It was the lower rings that were wrecked the most from the thermal expansion on my engine.

fec94b0712260ac7df12f37455bfbb12.jpg

]]>https://wibimmers.com/post/80708https://wibimmers.com/post/80708Sat, 17 Jun 2017 21:10:16 GMT<![CDATA[Reply to M20 scratched cylinder on Sat, 17 Jun 2017 20:14:45 GMT]]>

Snap said:

It isnt ideal, but boring it out and getting oversized pistons is not a budget-friendly situation.

I say run it for now and if it ends up it has a little to much oil consumption/blowby/too little compression then you can buy a used engine or build another one on the side and do everything right.

Yeah I think that is going to be the plan, slap it together and see what happens. Any opinions on ring gap?

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]]>https://wibimmers.com/post/80706https://wibimmers.com/post/80706Sat, 17 Jun 2017 20:14:45 GMT<![CDATA[Reply to M20 scratched cylinder on Sat, 17 Jun 2017 19:50:43 GMT]]>It isnt ideal, but boring it out and getting oversized pistons is not a budget-friendly situation.

I say run it for now and if it ends up it has a little to much oil consumption/blowby/too little compression then you can buy a used engine or build another one on the side and do everything right.

]]>https://wibimmers.com/post/80705https://wibimmers.com/post/80705Sat, 17 Jun 2017 19:50:43 GMT