i'm looking at getting this running 2wd moto4 350 to swap the rear end with my big bear. also I have an Yamaha tri moto 225 shaft with a seized engine. I was wonder if the the engine could work in my tri moto 225.

 

I would look it up or call a Yamaha dealer to see if the two shaft have the same Parts number.

The rear end of a 350Moto4 and Big Bear should match up. There were not real changes to the Big Bear untill 1993 and even then I think the rear was untouched.