[tom tilson]

I am not having a problem here, just trying to understand why some of the engine manufacturers used to pin the piston rings. Did they feel the rings turned and were trying to keep the gap out of the exhaust port. Does anyone know whether piston rings, 2 or 4 cyc, actually rotate around the piston?
I am just curios and am looking for answers.
I was taught in school 47 yrs ago to never put ring gaps on the major or minor thrust side of a piston, but to start a little way, say 25deg from the wrist pin and place the gaps 120deg apart.
Maybe through the years, it has been determined that they do rotate, but if not all three uniformly, does it affect cylinder bore wear when all of the gaps line up? blowby? Tom

 

[30yearTech]

Usually piston on 2 cycle engines have locating pins in the ring lands and a mark on the top of the piston to show proper installation. This is to keep the end gaps lined up and prevent the end gap from getting caught in any of the ports in the cylinder.

On 4 strokes the rings do rotate around the piston, and it does not matter how the end gaps are installed because they do move and move quite a bit in a very short time. I saw this illustrated at a Briggs service school where they had a cut a way engine and they installed the rings with the gaps all lined up, then the engine was rotated (via an electric motor) for about a minute. When the engine was stopped all the rings had moved and the end gaps were no longer in alignment.