2004 yz450 piston has rotational "play", this normal?

Replaced the valve stem seals but had to take the head off. Inspected the piston to find that i can move it a little side to

side within the cylinder wall, but seems strange that i can move it back and forth in a rotational direction as well. Clockwise and counterclockwise.

No performance issues whatsoever, and the cylinder wall is slick as glass. Could this indicate wear at the top of the connecting rod where the wrist pin

inserts? Or this could be totally normal, service manual made no mention of this. Any ideas? I wouldn't think its normal. Just wondering because if the connecting rod is going bad, i would rather replace it now since half the engine is torn down. And if so is the OEM rod the best? Would also entertain the idea of a big bore kit.

The rotation is normal to an extent, and is mostly a function of rod bearing clearance. The manual does offer info regarding how to check the rod bearing clearance. It's done by measuring the amount that the small end can be rocked back and forth on the crank (NOT slid side to side, which is bearing side clearance). If you're concerned. you should pull the cylinder and check.

Everything else seems in good shape. Just replaced the valve stem seals (had to remove the head). Mega amounts of carbon buildup and even an oily residue on top of the piston. Valves were all within spec, and passed the solvent leak test. Cleaned everything, re-assembled, and it started on the second kick. If the time comes to really go internally, will probably do a total head rebuild and big bore kit. Will just ride and enjoy for now, and thanks for the info!

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now