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Thanks Karl, that was my thinking also.

G'day guys,

New here and joined to get some ideas to try and fault find.

Have a UXV500 for over ten years and 3500 km.  Has been a good unit.  Parking brake is stupid design and some rust developed in the rims issues but otherwise it has been a good unit.

Recently however, it has developed quite a rattle that is getting worse. Replaced the drive belt and gave that a clean out initially thinking it was a belt flapping but this did not change the noise at all.  Took the tray off, underbody protection and things to ensure it was not some heat shield or something rattling on something at a certain resonance and that helped us to be 95 per cent sure the problem is in the engine, and it sounds more top end than bottom end.   We have never done the clearances, being used to Japanese things that never go out of spec', so is this something they have an issue with?  Or a timing chain tensioner or something, does that go in these things..?  It is hard to tell how much power it seems to have lost over time, as I think it has been a very much gradual decline in power.  My place is very hilly so the 500 works hard to drag itself and some wood in the tray around my place even when it was new, especially compared to the MXU500 quad that has so much less weight to carry, but I am fairly confident it has lost a fair bit of grunt.  Thus could just be valve clearances gone right out of wack?  Are shims required or do they have adjusters to set the clearances and is this a common issue? 

Thank you for your time and your advice.