I have a 1987 fourtrax 250 with a slight metal to metal knocking sound in the head when at idle. I took the head apart to check the rod but found no play in it. The wristpin also seems to be fine. There is no up , down looseness I can find that would cause the knocking. Any idea? The knocking is only heard at idle and sounds like metal to metal slapping. Like a rod knocking but not as loud or hard.Not a tapping like a cam chain more of a slapping of metal. As far as I know the engine is all stock with maybe new rings.
Thanks for any Info.

 

I have a 300cc fourtrax that was making a similar sound. I thought it was a crank knock, so I began to tear down the engine. Upon further inspection I found a missing tooth on the gear on the crank that drove the balance shaft. Everything else checked out and that was where the knock came from. Maybe yours would be a similar issue, good luck.

 

Valve adjustment?

 

Thanks for the replys. I tore down the motor and bore the cylinder .002 install new piston & rings. Installed new timing chain and Ebayed a used crank. I don't know what the knocking was but its fixed now. $50 for bore, $55 new piston and rings (ebay), $25 new timing chain (ebay), $20 complete gasket kit (ebay), $25 used crank (Ebay). Not to bad for about $175 and have a rebuilt motor with no knocking.