Aluminum spacers should work fine. The first series early 851's had aluminum spacers between the swingarm and the engine block. Lou

I may be wrong but I think you will have to narrow the mounting bosses on the engine about 5mm on each side. The big block 900-1000 cases are wider than the 750 cases.Looks like the swingarm will work OK, the orig. cross brace was closer to the case and won't allow clearance for the rear exit exhaust.

Thanks Lou, that sounds pretty straight forward to do.

Looking at the swing-arm is there any way of identifying if this one is the type that cracked at the shock absorber mount? Going by wdietz186 comment, this may be a 900 swingarm that accommodates the exhaust?

When fitting the spacers to center the swing arm make sure to leave some extra end play. As the cases get hot and expand they can actually bind up the swing arm. Adding the spacer might make it worse. Thank Pat for re-reminding me of that lesson learned the hard way.
-Cranky-

It does look like an early 900 arm. The later ones had thicker braces going up to the upper shock mount.I wouldn't worry too much about it being an early one though,I raced my 900SS for about 10yrs. with the early arm['till the 100+ getoff tweaked it] and it still could be used if I straightened it. The thing to look out for is if the axle adjuster bolts are stuck,they are a real bitch to drill out if they break.
Neat looking project!

Could it be a 750 sport swingarm as well? Lou

Lou has the eagle eye! Yes it appears to be a 750 arm with the internal sliding blocks,just like the F1 arm.

Cranky, care to throw a rule of thumb number on that "some extra end play"? Something that could be measured with a feeler gage?
Thanks, Bill

Since the spindle size is the same as the 1100 engine, could this swingarm be from a 1990 900 Super Sport?

I would think the 1989 Nuovo 750 Sport would have a large spindle like an F1 engine case.

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I wonder what do these aluminium spacers look like? Will I need to have them made?