Compression loss on cylinder when rings line up Truth of fiction?

I had a Datsun van once that had the rings lined up when I pulled it down
due to failing on one cylinder. That piston had a great big trench burnt
down the side where the ring gap was, about 3/8 inch wide and burnt right
though the side of the piston. All the rings were lined up, including the
three part oil control ring set.

It had managed to get me home on three cylinders, once I had disconnected
the crankcase blowby pipe from the air cleaner and removed the air cleaner
(switch to hot air intake?) as the blown out oil had saturated the air
cleaner. It also left the best smoke trail you have ever seen all the way
home! (info for skywriters!)

There is a theory that the rings rotate whle the motor is running, but,
since when has the real world fooled around with theory?

I'd prefer to pull the cylinder and check what is really wrong rather than
trying to guess in the air. Remember it's a bit hard to pull over and check
under the bonnet on the side of the sky!

Hope this helps,
Peter


"test it" wrote in message
...
I have heard many people, including a couple of A&Ps, say that when
the rings on a cylinder all line up that the cylinder will loose
compression. This doesnt make sense to me because if the rings are
going to leak, then they would leak anyway. There is an air path
between each ring for the air to go.

The reason I am saying this is that my wifes RV-4 engine has a
cylinder that is reading 55 psi on the compression check. She was
advised to run it a few more hours and then recheck the compression
because the rings might all be lined up and be causing the low
compression.

What say the experts. Old wifes tale or not?

Regards,
Tom Velvick