How deep of a scratch in the cylinder will affect it?

[Detroit Dazzler]

I just pulled down a 029 that was run lean, and the jug cleaned up pretty good. All I have left is four tiny scratches, sorry couldn't get a good pic to post. I can barely feel them when I run my finger over them. Is this enough to cause a compression loss?

 

[o8f150]

personally if you can hang your finger nail in it after cleanup then its to much,, you can try it and see what happens,, if you loose any comp it won't be much

 

[cutforfun]

where are the scratches, if they are above the ports they will hurt compression.

 

[Detroit Dazzler]

where are the scratches, if they are above the ports they will hurt compression.

The scratched are above the exaust port. I think I might just pickup some rings a see what happens. Maybe might try working on it some more

 

[galde]

A shallow scratch will not hurt compression nearly as much as the ridges on the side of the scratch. A tiny ridge will produce a long gap in the ring-to-bore contact. I have had good results in compression restoration by truing up the bore by cutting down the ridges and leaving the scratches. Some have said that the scratches will tend to fill with carbon. I did one just yesterday. It was a discard at a dealer that now has 140 lb comp, and starts on the first pull.

 

[grantwolland]

depends on the saw i guess?

i just rebuilt an echo cs-370 for a buddy who accidentally straight gassed it. I put a new piston kit in it but it had one maybe two large scratches between the transfers and one of the ports all the way up and down the wall. no chrome whatsoever. however i got it tuned up and pops pretty strong for only 120 psi on the compression tester. maybe will hit 130 after the rings seat? 120 is plenty good for smaller saws in my experience. hell my old big homies and macs run 120 psi and are beasts! as far as retaining the 300 hour durability period...that will be the test if he'll cut enough with it to wear it out. but a 50.00 piston kit is better than a 150.00 shortblock(might as well get a new saw). course, the catalytic material in the muffler got melted out(don't know how that happened?!lol) and she got opened up in the process! hell she screams like she's in the 40cc class now lol...

 

[BSmitty]

A shallow scratch will not hurt compression nearly as much as the ridges on the side of the scratch. A tiny ridge will produce a long gap in the ring-to-bore contact.

Absolutely right! You'd be surprised how much you can get away with as long as you have a "true" bore and good rings.