piston ring end gap spacing ?

[40 Deluxe]

Originally Posted by BRENT in 10-uh-C

To answer your question, ...yes, but again most rings today are gapless so it is moot.

FWIW, we monitor high-performance engines closely during assembly and then in teardown. The ring gaps are noted where they were installed and where they come out. They generally do not move, and usually it is because the piston was inserted and twisted as the rod was connected to the pin.

So going the other direction, what causes the ring to rotate?? Compression pressures are not going to rotate it, and if the piston is moving in a straight line within the bore, unless the rod is rotating the piston slightly during the cycle, tell me what is moving them??

Hmmm... I think most gapless rings are only used in high performance engines, not production engines. Do you use gapless in your Model A rebuilds?
Which auto engines have the rod installed after the piston is inserted?
As far as why rings rotate, maybe temperature changes as the engine warms up? Not sure, but let me relate what I saw years ago. I was cleaning the muffler on an old chainsaw and started it with the muffler off. At BDC the ring was visible in the exhaust port so with the engine running it appeared to be motionless. Running at part throttle I could see the ring gap moving. The gap would appear at one side of the exhaust port, then move across the port and disappear. It did this several times a minute. Visible proof that rings rotate!