Do piston rings rotate on the piston?

[Dominik]

We did a 59 Cadillac motor once with STD size pistons where we had to skip the next overbore straight to the following... 30 over wouldn't clean the bore.

Which we only realized once first oversize pistons had arrived. Maybe we should have quietly inserted the 30 over pistons and close it up again. Can you imagine that ring gap?

BTW, the rings cannot be 100% round if your bore is not exactly matched. The rings get more oval when you compress them. Unless they are made to be round when they butt.

But then they might as well come exactly gapped to begin with?

Yunick says they rotate at BDC and TDC

[Barry_R]

Originally Posted by Dominik

Unless they are made to be round when they butt.

But then they might as well come exactly gapped to begin with?

They are round when they are made and finished. Then they get "split" at the gap. The gaps on presized rings are surprisingly close considering the variables involved - .020-.025 is common to see. That allows for some bore size variation while remaining in a safe working range - remember that a .001 bore size difference is .003 gap variance. They don't know if you're putting them into a mom & pop driver, a taxi cab, a hot rod, a boat, or a MD truck when they go into the box...

[xb-60]

It's simple....if it's a La Nina weather cycle, the rings rotate clockwise and if it's El Nino, they go anti-clockwise. And if the weather's stable, the bores wear oval shaped and the rings don't rotate. I did a PhD on this.
Cheers,
Glen