Hey everyone! 

Purchased this RMZ250 with the intentions to flip as it had “bad crank bearings”

previous owner said he was cruising in fifth gear when all of a sudden the bike bogged down. He clutched in to rev it up a couple times, and once releasing the clutch, the back tire locked up. 

Engine was previously disassembled by another mechanic in which I finished tearing it rest of the way down.

From my knowledge and analysis, I cannot see any reason why the engine would have done what the previous owner said it did:

- Crankshaft runout within spec and No up/down movement
- Crank bearings sound and spin over fine
- Transmission shifts through all gears, nothing bound up, bearings work smoothly
- Cylinder showing normal signs of wear, no gouging or pitting
- Piston (although has some carbon buildup) measuring accordingly
- Ring gap still well within the service limit
- Cylinder head, cylinder, crankcase surfaces all flat and look good
-Valves sealing properly, camshaft journals/bearings show minimal signs of wear. 

Attached images and video accordingly. Assembled the cylinder and bottom end together and all runs smoothly and feels fine. 

Will be cracking open the cases to get some piece of mind however all of this checks out. 

I cannot see why this engine would have locked up? Could it have been a fueling issue or such or am i missing something obvious?

Thank you for your time and hope I can get some help being un-stumped with this one!


Stumped on this 2012 RMZ250 Engine Service