I have a 2007 yamaha big bear 250 I bought recently for a steal it dropped a valve and previous owner took apart and lost most of parts is there another engine I could put in its place like maybe a 350 or 400 that will bolt right up? Any help would be great

 

I don,t think it would work. The 250 is a different motor unlike the 350 and 400 which are the exact same motor just with a different stroke. (64.5mm vs 71.5mm)

So the 250 would have different motor mount points and the rear end would have a different drive shaft positioning and size.

 

You'd probably be better off to find another Big Bear engine or all the parts (EBAY!) and put it back like it's supposed to be.

 

So I started making a big bear tracker 400 this weekend yes there's a lot to change .motor mounts the whole rear end had to be swapped I had to add 2" to the swing arm connection point. That's all I've come across so far. Just a backyard project. I want something different than everybody else and I like my bear trackers.