Friend did a top OH after a prop strike.
They borescope after oil burn started to increase dramatically and found this (pic)
O470R
Cylinder, piston , rings all are 50 hrs since new
Strange pattern in cylinder and high oil burn, 1 quart per 2 hrs of flight.

Any ideas?

I had something very similar 60 years ago when I put new rings in an old motor. When the old mechanic looked at it he just laughed and said "Kid your piston groves are worn out and you installed a ring in upside down and that is called ring chatter". New pistons and rings installed correct and I was off and running. Your situation may be entirely different but that was my experience.

two things...

One.. Exactly what 175 magnum said. Rings installed upside down. If it is that then the pistons are now probably junk. Replace rings and pistons. Hone the cylinder and re-install.

Two.. Ring gap, I have seen them chatter and also break due to improper ring gaping. A broken ring will cause excessive oil consumption.

Brian.

Yup, what Brian said!!
John

As said above, it’s ring chatter.

Another possibility for the cause of the chatter. The ring groove is out of spec which allows the ring to tilt in the groove. If the pistons are not old and worn out or manufactured incorrectly another possibility is that the engine was ram lean which overheated the pistons and caused the ring lands to fail. This would allow the rings to tilt and chatter.