Engine Swap Question

[Sisyphus]

So I just blew up the engine on my 79 standard. I'm looking for donor candidates, and was wondering what the most compatible years are. Or, which years would NOT work or make my life harder. Thanks so much for any help!

 

[5twins]

'74 -'79 would be most compatible.

 

[cooltouch]

I would go with a '78 or later. Yamaha changed the gear design in the transmissions beginning in '78 and to maintain that level of compatibility is mostly why I recommend the later motors. Also, if you think you might ever want to install MikesXS's OD 5th gear (to drop the engine revs for more comfortable highway cruising), it will work only with the '78 or later tranny.

But first, you should find out exactly what happened to your motor. The XS650 has a pretty stout bottom end. It might not be all the difficult of a fix to get it running again.

 

[XSLeo]

He has a 79 engine, so if he wanted to use Mike's 5th gear he can put his 79 gearset in most any year engine.
I agree with 5twins the 74-79 is the easiest swap. The 80+ engines will need the bushings to support the advancer rod for the points. Not to hard to swap out, or put in new ones.
On the earlier models I think they will swap right in too. There is something about engine mounts, but I think as long as the mounts match the frame, the engines swap fine.
The first two years 70-71 had no starter, the 72-73 have the starter and decompressor.
The pre 74 engines also use the 256 crank, longer rods and shorter pistons, different rings. Harder to get the parts.
So the 74-79 is the best option.

 

[Sisyphus]

Thanks so much guys. This is extremely helpful.

 

[cooltouch]

The 80+ engines will need the bushings to support the advancer rod for the points. Not to hard to swap out, or put in new ones.

Ah yes, forgot about the points. Riding an '81 SH for so many years, it's easy to forget about 'em.