I've had my Fourtrax trx350d 89 model for about 8 years. (not used very much)
Its always had a tap/rattle/knock in the engine. It does sound metallic. It is quite loud!
At idle its not too bad, but gets louder when revved, with or without load.
I've done the tappets several times over the years, but not helped.
I've tried to isolate the noise with a mechanics stethoscope, but it sound similar all over the engine.
A few years ago I took the rocker cover off and found the cam was badly worn through the bearings, several mm of wear! I line bored the journals and re bushed the ends of the cam, made phosphor bronze shells for the ends. And it all went back together like new. That must have clearly been the knocking noise as the cam could dance all over the place, or so I thought! It didn't make any difference to the noise, it was still there!
Yesterday I decided I better have another look, the chain is tight, the tensioner is working correctly with plenty of reserve travel.
So I pulled the clutch side casing off. Chain, clutches, gears all looks ok. There is a fair amount of end float in the crank. No side to side, or up and down, just end float.
Hopefully seen in this video.
What do you Guys think?