Quote:
Originally Posted by elgyqc
I only know what I have read... but I have read more than once that bore scoring starts at the bottom of the cylinder.
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It did on my CSS. The thought is the cyl is too short at the bottom and too much of the piston is exposed below the cyl at BDC. When it heads back up for the compression cycle, it rattles a bit before it fits back into the cyl. The rattling means the piston and cyl are scraping against ea other, which wears the coating off each and starts the scratching effect that worsens with more cycles because it's alum on alum now.
I thought I had some pics of my #6 cyl but I couldn't find any. The shop that confirmed my BS said there was a thin crack developing in the cyl and would have eventually chipped off a section if I'd ignored it. And this was on the bottom of the cyl, so I couldn't see that from on top with my scope. The scratching had gotten so long I could see them with the piston down, but you don't see the worst part from above since it's hidden by the piston.