Strange engine event

"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?

--
Jim Carter

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

"Jim Carter" writes:


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.

Very Clever Design. I can't recall the details, but ISTM there are
[automotive] patents on making 'em creep along.

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

It does leak lots more; the gap between the rings is not all that
far, I guess...

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

perpendicular to the cylinder wall, there must be some other mechanism other
than just piston movement causing them to rotate.


I just can't get it into my head how that a ring can be put in and when the
engine is torn down all of the grooves will be in the same place as when
installed.

The keepers on a two cycle boat engine (not motor) are the only anti - Rotation
device that I have seen.

Dave,
I've torn engines down before and the distance between the rings is
relatively a lot more than the gap between the ends of the ring when
compressed into the cylinder. It is such a big difference that I don't see
how the intra-ring distance could be restrictive to the flow of gasses
passing through the ring gap.

I'd really like to see some information on the "Very Clever Design" you
mentioned. Even if the cylinders were honed with a diagonal pattern,
shouldn't the ring just reverse direction at the end of the stroke and
follow the honing marks?

--
Jim Carter
"David Lesher" wrote in message
...
"Jim Carter" writes:


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.

Very Clever Design. I can't recall the details, but ISTM there are
[automotive] patents on making 'em creep along.

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

It does leak lots more; the gap between the rings is not all that
far, I guess...

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

"Jim Carter" writes:

I've torn engines down before and the distance between the rings is
relatively a lot more than the gap between the ends of the ring when
compressed into the cylinder. It is such a big difference that I don't see
how the intra-ring distance could be restrictive to the flow of gasses
passing through the ring gap.

I'd really like to see some information on the "Very Clever Design" you
mentioned. Even if the cylinders were honed with a diagonal pattern,
shouldn't the ring just reverse direction at the end of the stroke and
follow the honing marks?

--
Jim Carter
"David Lesher" wrote in message
...
"Jim Carter" writes:


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.

Very Clever Design. I can't recall the details, but ISTM there are
[automotive] patents on making 'em creep along.

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

It does leak lots more; the gap between the rings is not all that
far, I guess...




I don't recall much more. I'll ask a friend who knows lots more
than I do on engine innards. But it was Detroit, not overseas...






--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

The piston really only approximately goes straight up and down.
Engines are not perfect machines. If you looked at the general
dynamic alignment of everything on the microinch level etc, there is
probably a slight amount of rotation inherent in the structure of an
engine including the crankshaft and rod deformations. When combined
with the varying pressure fluctuations on each ring, the ring
gradually rotates
in one direction or another. Remember you are dealiung with something
that is cycling back and forth 40 times per second, so that it doesn't
take very much rotation each cycle to give a lot of eventual motion.

Put it another way - why shouldn't it rotate?

I don't think it should rotate because the action of scrubbing against the
cylinder walls will wear "micro" grooves in the rings that match up against
corresponding ridges on the cylinder wall. If the rings rotated there would
never be this ridge/groove result. Since you can see and sometimes feel the
grooves and ridges, I can only assume the rotation of the ring is not
happening.

--
Jim Carter
wrote in message
om...

....

Put it another way - why shouldn't it rotate?

In article ,
"Jim Carter" wrote:

I don't think it should rotate because the action of scrubbing against the
cylinder walls will wear "micro" grooves in the rings that match up against
corresponding ridges on the cylinder wall. If the rings rotated there would
never be this ridge/groove result. Since you can see and sometimes feel the
grooves and ridges, I can only assume the rotation of the ring is not
happening.

That is why cylinders get a crosshatch pattern during the honing
process. The microgrooves go around the cylinder, not parallel to its
major axis.