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Originally Posted by olddog
I'm sure the rings would make a differance, but back in the day (60's & 70'S) I have pulled engines with 100K miles apart that had 0.030" taper worn into the cylinders. Generally the bottoms of the bores would be way out of round from the thrust of the piston skirts.
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I ran an Automotive machine shop for several years in the late 60s into the mid 70s and again in the later 80s. It is my recollection that most of the wear is at the TOP of the cylinder( that's why the lip). The heat ,etc. makes the wear more prominent at the top. Piston skirts of aluminum are going to wear themselves away much faster than it could ever wear the wall. That's why they went to aluminum from the cast iron they used to use for pistons. The rings, always under extreme tension to keep a seal, are much harder and do much wearing. If you examine a worn cylinder closely, you see that the wear starts at the top and tapers off to less wear as you go down, hence the word taper. The wear in a cylinder, while not exclusively in the ring travel area, is mostly confined to that area. I will credit some of the newer ring coatings for some of the reduction in wear also. But the low tension rings have more overall impact on wear reduction.