This 4-wheeler sounds and runs perfect. It has lots of power and doesnt smoke or miss. Then at about half throttle or when it is under load it makes a piston slap noise and starts vibrating badly. sounds like the motors going to fly apart. I thought it was piston slap but it doesnt go away when warm or even hot. The faster I go the louder it gets if I bring the throttle back down to half way or so it stops. So I thought maybe it was the rod bearing but if that was the case should'nt it quit under a load or always make the noise? I just had it apart a week ago and seen nothing wrong. The rod bearing was tight, the piston was tight, the rings looked good, the timing chain is brand new, ect. So now i'm thinking something in the head just need a second opinion. Has anyone else had this vibrating with a noise problem before?

 

Have you checked valve adjustment? Chain tensioner extending like it should?

 

Hey endo, thanks for the responce. The chain is tight so I don't think that is the problem. I'm getting ready to adjust the valves so i'll let ya know how that goes. Hopefully thats the problem.

 

There could be a possibility of the crank going south,my Wolverine made some pretty unusual noises before I broke down and sent it in for the total rebuild and a 446 kit, but unlike yours, mine was not running fine, it was down on power, didn't smoke, but felt like it missed a lot. The guys at FST told me the crank was pretty shot. Vibration at certain rpms could definately be a worn crank finding its "harmonic" frequency, vibrating only at a certain range.

 

I think your right. There is nothing wrong with the valves, piston, cylinder, chain, wrist pin, rod and the oil pump is sending plenty of oil to the top. The only thing left is something in the bottom end. Im going to change the flywheel and check the clutch basket. I guess the clutch basket could of lost a chunk and knocked it out of balance or the flywheel lost a counter weight or something.
If it's not that I think it'll be time to get rid of it. lol.

Oh, I just thought of something. I'm pretty sure I didn't but I wonder if I put the piston in backwards if that would cause it to be out of balance somehow or maybe cause it to hit the valves at high rpm's??

 

You hit the valves at high rpm, and you will come to a halt real fast, I had a valve keeper come out when I was running my motor after a top end rebuild, bent that sucker instantly, and damaged the top of the piston as well.

 

I have had my exhaust pipe start splitting a few inches away from the motor, and when I hit the gas hard it would sound almost like piston slap. The pipe was so dirty it took me forever to figure out where the noise was coming from. Also I had a head gasket blow one time that sounded very similar.

 

I found the problem. I know this sounds crazy but the timing chain was so tight that it was draging accross the plastic adjustment bar slider (can't think of the name of it). Anyways, I never thought that would have caused a problem but looking back now I guess it would. When I put the new chain in i gave the adjuster a little help by pushing on the chain until the adjuster clicked a couple of more times. Don't do that it's a bad idea. lol
I guess by all the draging and friction that's where I was getting the vibration and noise. Thank's for all your help