ATV is a 2002 Prairie 650 4x4.

Engine stopped dead while riding. It will rotate freely about 270 degrees.

Rear cylinder valves all move, so rear cam chain is fine. Front cylinder intake valves move fine, so I know cam chain is OK.

Engine fails to rotate just at the point where the front cylinder exhaust valves should move. Those valves do not appear to be stuck down at all.

Any ideas as to what might be jamming the engine up? Also note, the engine stops at the SAME place EVERY time. Not sure if it is gears not meshing (piece caught in an internal gear), or a valve broken?

Any suggestions appreciated!

 

Remove the valve clearance inspection cover and make sure ALL rocker arms move up and down as you slowly turns the crank. If any of them does not move, that might be a dropped valve. If not sure or can't be checed that way, it's time to remove the head. I think somthing's gone wrong in the top end like dropped valve.

 

One of the exhaust valves broke on front cylinder. Head and piston are trashed. I found a used cylinder head, piston, and cylinder itself. I will post back to see if I can get it all put back together!

Daniel

 

Installed the used head, cylinder, and piston. Except for the used head having bent exhaust valves (which I replced), all went well, and the quad is back together and running well!