1998-2001 Yamaha YFM600FHM Grizzly Factory Service Manual, Page 232Get this manual
TROUBLESHOOTING
IDRIV 1.c1
Too-little gear lash is extremely destructive to the gear teethIf test ride following reassembly indicates this condition, stop riding immediately to minimize gear damagec.A slight "thunk" evident at low speed operationThis noise must be distinguished from normal machine operationDiagnosis: Possible broken gear teeth
A WARNING
Stop riding immediately if broken gear teeth are suspectedThis condition could result in the shaft drive assembly lockingup, causing loss of control of the machine and possible injury to the rider
2.lnspect: Drained oil Drain plug shows large amounts of metalParticles -7 Check the bearing for seizure