So I picked up a Yamaha Warrior this last summer for $400 bucks. It had some flaws but I fixed it up and got it running great! This last fall before I was going to put it away for the winter, I noticed that the four wheeler began to make a loud banging sound when I would turn over the electric start and it would make a loud bang when I shut it off and then spin the starter. I took it apart to find that the jackshaft post had cracked on the stator case and on the transmission case. At the time it didnt bother me much, since i had a second engine. I swapped out the cracked cases for the good cases and the electric start worked good for awhile. Then it began making the loud banging sound when I would turn over the electric start and it would make a loud bang when I shut it off and then spin the starter. I recently took it apart again and found the jackshaft to be broke in half and that both cases were cracked yet again! For this to happen once I understand, but for the cases to be cracked again, this is a reoccuring problem.
Anyone have any ideas?

 

are all the bearings ok in the case?? and are you sure? a crankcase doesn't crack for no small reason, something is loose, works it's way loose or a bearing is shot. Where exacally does it crack?? and when? while your shifting? these countershafts are not easy to break.

 

Give me your email and i will send the pictures to you of the problem. My email is skatike27@yahoo.com