I have a '10 YZ450, that broke the 4'th gear, and ruined a bunch of other transmission parts. So I bought another '11 motor from E-bay. When I got that motor, I found out that the left side case was broken, so I decided to split the case on both motors to swap cases. Then, I discovered that the[SAME 4'th gear was broken in the '11 motor as well! It looks like this is a common problem with these '10-'13 motors.
BTW, do not do any dealings with TERRY HARDISON out of CA. He is the &%$#@! who sold me this motor claiming it was a perfectly good motor. He is currently parting out 2011 YZ450.
Edited by yam314, March 15, 2014 - 11:21 AM.