I have a 96 Fourtrax 300 that has a knocking noise in the top end? I'm fairly confident its the piston But figured I'd ask a few Questions! I have heard this same noise in one other fourtrax and thought maybe it was common? It only has 85PSI of cranking compression, I'm not sure what it should have but this seems low? The noise is a little deeper noise then a valve train noise. Anyone ever have this problem? Thanks for any info in advance!

 

ya i have a 300ex and noticed that noise as well. you have a loose chain or a loose bolt. try checking that and make sure everthing tight.

 

You should have at lease 150 PSI. If its really at 85, you need to rebuild you motor. I did myne 2 months ago and changed my cam chain also.