The Diagnosis

Tonight I decided to see what was keeping the YFM225 from shifting correctly. If you will remember the former owner claimed the YFM stopped shifting after trying to pull start it. With the engine on the bench I pulled the crankcase cover and inspected the shifting shaft and shift cam. This all looked good so I decided to open the sub-transmission cover. As I cracked the cover I noticed the remains of a bearing sitting in the lowspot of the sub-transmission where the shift cam comes through. I pulled the middle set of gears out and found the bad bearing. Luckily the outside race was still whole and the structure around the race, although beat up, was not damaged to a point that if could not be used. The inside race was almost completely destroyed but surprisingly the shaft had no damage. I was able to slide the damaged race off the shaft and with a little work, pull the outside race out of the case. I was very lucky that there was not more damage done to the sub-transmission with a gear jumping around inside. I split the case and inspected the primary gears, shift cam, and shift forks, which all looked good. With the debris not impeding the movement of the primary shift cam, the gear movement worked well and slipped into all five gears. I put the two halves of the case back together and called it a night.
I will not only order the bearing that came apart but will replace corresponding bearing on the other end of the shaft.