Xiaotao, For the valve lash to cause the gear to slip I believe it would have to be very tight lash to add load to the cam rotation. From the looks of the shaft and the amount of heat I think the issue was caused by lack of lube possibly from some debris in the oil system. This may not have happened just before the gear slipped, it may have happened previously and the gear just now broke loose. The gear slipping should not be the cause of the excess heat in the bearing and shaft and more of a result of the bearing and shaft issue. Dan