Piston-Head interference Issue

[bmw633]

Hi,

I disassembled the low compression engine and took the head, camshaft, cylinder and head to a machine shop to have them do a valve job, rehone/rebore the cylinder and fit new rings in it. The machinist noticed a place on the piston where it had contacted the head. It is in the area between the exhaust valves in the flat area. He asked if I had run it without the head gasket, which I hadn't. He said there may be some vertical play in the connecting rod, and I checked and only found a little lateral play, which is within normal limits. Not knowing the history of the engines, I don't know if the heads had been shaved or if the head is warped, causing the interference.

I went ahead and gave the machinist the go ahead to do the work. I have two bottom ends. The original engine is the one the exhaust valve broke off and grenaded the engine. The other is an EBay dud that PinWorm Cycle Parts would not give me any credit on. The engine ran good for 100 miles before it started lagging, topping out at 52mph. Only 110 psi compression.

Any thoughts/suggestions? I really hate throwing money at this bike. I want it to be dependable, like all of the other Jap bikes I have owned.

Seth Anderson
Moon, VA

2001 Suzuki GZ250
2012 Honda NC700X
1991 Honda ST1100