How To Check Piston Rings

[bmw633]

Hi,

I have an 2001 GZ250 with 10K miles, and the engine suddenly has lost power. I pulled the head and everything looked ok to me, no broken rings, the valves appear ok. Carbon buildup on top of piston, which I assume is typical.

I cleaned everything and reinstalled the rings, and I used the old head gasket and torqued it down, according to specs. It started ok, but still doesn't have good power, only topping out at 45mph. I set the crank at TDC and then lined the cam according to the marks. It sounded different when I started it, like maybe I am off a link of cam chain. Is there a way to check engine timing without disassembling the engine?

The cylinder walls looked ok to me. The shop I took the bike to compression tested the engine and it only had 110 psi compression before I tore the engine down. I took the head, cam, and cylinder to a machine shop and he kinda looked stupid, said he didn't work on things like that.

How do you know the rings need replacing? Should I just buy the 0.5 or 1 oversize rings, and maybe hone the cylinder walls and put it back together?

Seth Anderson
Moon, VA