Piston Ring Positioning

[wsa111]

[THE FRENCHTOWN FLYER]

This is good info, and is a good practice to follow on a new build-up. However I have discovered that piston rings may rotate on the piston ring grooves during normal engine operation. Thus there is no guarantee that the rings will stay positioned as installed. While working as an engine development engineer I discovered this on a dynamometer experiment specifically set up to investigate this issue. A 5.0L V8 was blueprinted and assembled with the rings oriented as shown in the diagram. After several hours of operation - I forgot how many - the engine was carefully disassembled and the gap locations recorded. Most of the gaps had changed positions. I did not determine how fast or how many times they rotated. I did not determine if all the rings rotated at the same rate. I did not determine if there were any specific anomalies in the piston design or manufacture that contributed to this phenomena. All I can say conclusively is that the rings DID rotate. But as far as spacing the gaps as shown all I can say is "It wouldn't hoit."

[CNC-Dude]

Yes FTF, rings do rotate on the pistons as they move up and down. That's why most 2 stroke engines have a pin in the groove so the ring won't rotate and hang up in the cylinder ports. The initial spacing is really unimportant, but to spread the gaps far enough apart to prevent the likely event they align with each other. At some point they probably do, but each ring rotates at different rates and amounts so they probably don't stay aligned with another rings gap long enough to cause any problems.