my 2cnts
Awesome thread
Awesome people here.
Thought I would chime in with a few of my issues with a 97 600sx
Oil pump:
Make sure you get a 98 or later model pump.
The 97,s had a recall for excess oil use.
This happened to me, oil pump started really pumping oil, was so much that I burnt a piston, oil ratio was so high that is would run lean, too much oil, fuel too thick = jets wont pickup fuel like they should.
Brace on PTO side of frame:
I noticed in a later picture (One where sled is together with rebuilt motor) that the hack job brace was not installed.
The frame for sure should be repaired properly, but if not done yet I would for sure at least install the brace that was there before (As bad as it is). You were having clutching issues and if the frame is not correct your clutch alignment will never be right.
Bearings:
You have spent so much time and effort so far I would for sure replace all the bearings in the chaincase, jackshaft and drive axle. Just not worth the possible damage that a failed bearing can cause. And based on the abused nature of the sled what are the chances they are any good?
I have always replaced these on my sleds at 2500 to 3000 miles as a matter of normal maintenance. Had a couple issues years back and learned the hard way just do em. The damage caused by a failure is always way more expensive.
My 97 600sx has been a great sled. After I rebuilt and got the new oil pump (around 2000miles) I have over 8000 miles on it. Use it as a backup sled now but always reliable.
Was it raced?
Maybe but the 600 Yamaha twins were not the fastest sled around.
Probably just a terribly abused sled owned by someone with 0 patience or mechanical skills.
Good luck going forward