On Fri, 25 Jun 2004 14:03:16 +0000, Jim Carter wrote:

"WARREN1157" wrote in message
...
The piston rings rotate whilethe engine is running. The grooves on all of
the
rings could have aligned up with each other for a little while and then
rotated
back into un - aligned positions. If thei happens reguarly the cylinder
could
be out of round.

This condition would make CHT go up and EGT go down

What causes the piston rings to rotate? Since the piston movement is
perpendicular to the cylinder wall, there must be some other mechanism other
than just piston movement causing them to rotate.

Also, why would the grooves on the rings have to be lined up to allow
leakage through the groove?

On car motors, isn't this the reason the that you hone and crosshatch the
cylinder wall? That way, during breakin, the rings are encouraged to
rotate and mate in such a manner? Once the rings mate, they'll naturally
want to follow the same rotational, mated path. I ***assume*** the same
thing is done with plane engines. I believe the closest analogy would be
to picture a bullet in a barrel, where the spin in placed on the bullet by
the rifling. Now, just imagine the bullet traveling back and forth in the
barrel, whereby, it natually wants to rotate along the length of the
barrel, in spite of the direction of travel.

Any AP guys, feel free to correct as needed.

Cheers,

Greg