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I always wondered why the overhaul manual requires you to attach the pistons to the connecting rods before installing the cylinders, so that the numbers on top of the pistons face toward the front of the engine. Why is that?
Our friendly A&P/IA says it's because the pistons are asymmetrically weighted for better wear distribution. So, if you put them on wrong, i. e., reverse rotated by 180 degrees, you get excessive wear.
Some pistons are cam-ground so that when running at full heat they round out and fill the cylinder more accurately, top and bottom, but that wouldn't have anything to do with a north-south installation at the piston pin, I don't think.
Well, I tore into an engine recently where the previous rebuilder hadn't paid any attention to that requirement. But I couldn't get any input from him that it made any difference. What HAD made the difference was that he had installed O-200 pistons in a C-85-8, and the engine would hardly even run. He had "de-stroked" a C-85 to a compression ratio of something like 5 to 1.
Our friendly A&P/IA says it's because the pistons are asymmetrically weighted for better wear distribution. So, if you put them on wrong, i. e., reverse rotated by 180 degrees, you get excessive wear.
Some pistons are cam-ground so that when running at full heat they round out and fill the cylinder more accurately, top and bottom, but that wouldn't have anything to do with a north-south installation at the piston pin, I don't think.
Well, I tore into an engine recently where the previous rebuilder hadn't paid any attention to that requirement. But I couldn't get any input from him that it made any difference. What HAD made the difference was that he had installed O-200 pistons in a C-85-8, and the engine would hardly even run. He had "de-stroked" a C-85 to a compression ratio of something like 5 to 1.
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