Someone brought a Yamaha Grizzly 550 ATV over for me to look at. They said that it made a bad grinding sound and became very hot when they drove it.
I took a look at it and noticed that the top of the engine was covered with black dust. This machine, like a lot of newer ATV's, uses a belt drive CVT similar to the drive train on a snowmobile. On closer inspection the dust looked like the residue from a worn out drive belt. I took the cover off the clutches and discovered that a bolt had come loose and had been rattling around inside the cover. The belt was destroyed and the clutches are beaten up pretty bad.
The machine will need a new belt and I am going to recommend to the owner that the primary clutch be replaced. There is not much labor in this job, but the new clutch will be expensive.
Interestingly, this is the third Yamaha with clutch problems in the village in the last few months.