Do rings (and valves) move from original position?

[Gunter]

Someone with lots of rebuild-experience has told me that rings DO NOT move from their install-position on the pistons.
I tend to believe that; why else is care taken to position the rings if they move anyway?

Also, it is my understanding that the rocker arms hit the top of the valve stems slightly off-center to purposely turn the valves to achive even wear on the seat.
Is this correct?
If not, how else are the valves encouraged to turn during operation?

Expert opinions, please.

[john walker's workshop]

they both move. the valves are designed to rotate and there's nothing to stop rings turning, but really nothing to make them turn either, so it's more gradual over time. a 3 cylinder 2 stroke DKW i had used a pin in the ring gap to keep them in place.

[Gunter]

Thanks John:
I remember the 2-stroke Deutscher Kraft Wagen with front wheel drive, I think.
Pretty good performer but real stinky and became verboten because of clean air issues. DKW became Auto Union many years ago and now is Audi. The original Sweedish Saab started as a 2-stroke (FWD) and had to change with the times.
How exactly are the valves made to turn?
Is it because the rocker arm hits the valve stem slightly on edge and, in moving downward, the sliding movement turns the valve a little bit each time?
That would explain why the top of the stem is flat and not rounded off.

[Wil Ferch]

DKW, Wanderer, Horch, and Audi...all merged to become Auto Union in the 30's. That's why there are 4 interlocking rings for the logo. Audi is the "survivor" today...

- Wil

[Zeke]

All 2-strokes using a port system have the pin. The ring gap cannot be allowed to move over to a cylinder port or they will catch on the opening. Hence, they are known to rotate.

I think you want the valve to rotate, not so sure about the rings.

[Gunter]

Yes, I agree that the valves should rotate for even wear; that's advantages and I believe it is designed that way. Next time I am in there, I'll look closely how the rocker arms contact the valve stem so I understand how the rotation is achieved.
As for the rings, they may very well move somewhat even though one wonders why. An engine builder with about a hundred rebuilds told me that the rings really don't move. Of course, it is preferred that they keep the staggered position but not much harm is done should they move. Thought?

[304065]

If you check the late, great Harry Pellow (the "Maestro" of 356/912 engine rebuilding) web site, there's a great story about how the ring gaps inadvertently lined up due to ring rotation, and burned a nice hole in the side of the piston due to combustion gas blowby.

I remember an apocryphal story about a visitor to a BMW plant in the 1970s, where an apprentice laborer was using a straightedge to ensure that the ring gaps lined up exactly, not 120-degrees apart! Wonder how long that engine lasted before it blew up.

Anyway, my understanding is the rings do move, which is why the 120-degree orientation is critical to start with, to give yourself every possible chance of them NOT aligning.

[Gunter]

Thanks John, that makes sense.

[911pcars]

I'm unconvinced there's a system in place on a 911 to rotate the valves on purpose. If anything, I suspect it's more random. Since the valve is always under tension when it's open, the rocker arm would have to exert side pressure on the periphery of the valve tip as well as a wiping action as it pushes it open - not enough of either IMHO.

I'd be interested if anyone has knowledge of marking valves or retainers before and after a rebuild and documenting any consistent movement. Maybe mark the valve retainer next time you perform a valve adjustment, then observe where the marks are at a later date.

There used to be an aftermarket (or factory) device that automatically rotated the valves. I recall it being part of a valve spring seat.

Sherwood