Posted by mark dingbaum on Thursday, March 11, 2004 at 2:06PM :
In Reply to: When is right time to bore an engine? posted by David N. Lundstrom on Thursday, March 11, 2004 at 12:57PM :
Hi,
It's probably not an out-of-round condition that causes the problem but rather the taper from bottom to top. If the rings have to expand and contract as the piston cycles up and down, the rings wear quickly and don't seal well.
Want a number? I don't have one handy. A very wild guess might be ten or fifteen thousanths 0.010 or 0.015 difference in measurement (diameter) from a worn to unworn area of the cylinder. Any scoring would probably require a rebore even if unworn.