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Crank Rotation

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The plug for the decomp hole popped out of my head. I got about a lap in before I realized it was blowing oil out. I have a 2004 cylinder head from a yz250f on a 2006 motor (runs great). While I was cleaning the head, I checked valve clearance and shimmed two valves. When i put my ratchet on the crank to turn the motor around to verify valves weren't hitting the piston, i noticed a notchy feeling. Its when the piston is almost BDC and the valves arn't open. Its ever so slight. I'm worried dirt got into the bottom end or something. I'm 100% sure it has nothing to do with the valves. The bottom end has 54 hours on it. The cylinder and valves only have 20 hours. I didn't notice any play in the crank when i took the flywheel off to replace the cam chain. Has this happened to anyone else? Any ideas as to what it might be? Is there an easy way to find out whats going on without pulling the motor apart?

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I have not lost that plug, but a friend had one work loose.  These engines are close tolerance, meaning that there is not much margin for loose components in the rotating assembly.  Do what you want, but for me, I'd tear it down and inspect.  I'd look specifically first at the con-rod bearing, then crank main bearings.  Next I'd check the piston pin clearance in the piston AND the small end. I'd look for any signs of interference between the piston and crank flyweights, like its touching, or cracked piston skirt.  Last, I'd pull the oil pump apart and look for any scaring, might replace gearrotor assy, and I'd clean the flywheel magnets and keep and look for any metal stuck to it and determine if aluminum or steel.  Precision measuring tools might be used to check for excessive rod up and down movement on the big end bearing.  Due diligence, good luck.  Hopefully its not the crank.... cross your fingers.

Edited by ronbuell

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