M20B25 scratched piston

[tommye]

Does anybody know why my pistons are scratched like this? The right one.
Picture is of the worst one.

And one more question, witch con rods is the best to use?
The left one from a M50 or the right one, the current ones from my M20.

[devon.818]

how do your cylinder walls look?

[tommye]

the cylinder walls are perfect,
hone cross pattern still visible no other scratches.

[devon.818]

i dont really know a lot...but someone else will chime in...could it be blow by and bad piston rings??

[jlevie]

Light scoring (like that) on a piston is common and not anything to be concerned about. When it comes to cylinder wear, don't trust your eyes. Use a bore guage with tenth of a thousandth resolution to check to taper and out of round. In most cases the top of the cylinder will show the least wear and lower down is where you'll find the wear.