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Discussion Starter · #1 ·
Does anyone know if they used a different chaincase cover between 90 and 91? I'm wondering if the 90 cover will fit over the much larger upper sprocket nut on a 91 jackshaft.

If you're wondering how I ended up here... in my "mid speed bog" posts on my 1990 Indy 650 you might have noticed where I mentioned the jackshaft bearing coming loose...

Well it did it again, cracking the bearing sleeve this time (I'm sure most of the damage was from last time though). The jackshaft spun enough to grind away 0.045" from the shaft, the 3 shim washers between the driven clutch and bearing got ground up into dust, the upper sprocket bolt was almost falling out and when I pulled the shaft out I found the key & keyway's holding the brake rotor were completely toast (don't know what was holding the rotor in place - the key came out in many pieces and the snap rings had fallen off).

I called around and found a place (a 1 1/2 hour drive away) that supposedly had a pile of used jackshafts for 80's and 90's Indys. When I got there I found they all had spline mounted rotors (91 up). I ended up picking up a shaft and rotor (spline mounted rotor, large nut with cotter pin holding upper sprocket).

To make my life more miserable, their calling for heavy rain Tuesday and according to my shop manual I'm missing a spacer that goes behind the rotor and a sealing o-ring.

I guess this thing's not going to be together this weekend...

Any info on that cover?

Steve S.
http://home.off-road.com/~ovo/members/sshaw/sshaw.htm
 
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Discussion Starter · #2 ·
Steve,

At this point I'll say they ARE the same basic peices. I can let you know better tomorrow morning. My 90 650 has the old style chaincase/caliper mount, but I beleive it uses a castle nut on the top sprocket. My 96 Ultra has the newer chaincase (obviously), and thanks to a reverse kit the cover is off the machine. As my 650 is torn down right now, I can easily compare the two tonight.

For reference, my buddy has a 92 RXL with the same chaincase as my 96.

 
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Discussion Starter · #3 ·
Better double check the gear spline. Polaris has two different size wholes on the 13 wide gear sets so you may have to change the top gear. Don't sweat it though if you use the larger one it is the same as the HYVO stuff. I have had a bad time with that bearing on my Storm, had to replace the shaft twice. Finally went back to the old style bearing with the lock collar instead of press fit and set screws.

 
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Discussion Starter · #4 ·
Steve,

I guess I was wrong. My 1990 piece is stamped, while the newer one is cast. The stamped piece has two "indents" that appear about 1/8 inch deep, on the cast peice the lower indent is about 1/4 inch deep, and the upper is about 3/8 (or more) deep. So, there is a considerable difference in the two parts, probably the difference between a bolt and a large nut! Sorry I didn't have better news.

 
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Discussion Starter · #5 · (Edited)
90/91 Chaincase upgrade

Just before Polaris discontinued the chaincase with the stamped cover they did a upgrade. The jackshaft was changed to the style with the castle nut and seals were added to the top and bottom shafts. The cover was also changed to accomodate the added length of the jackshaft. The cover is easy to identify, instead of the small dimple it protrudes at least half an inch.

http://s244.photobucket.com/albums/gg25/nitro-express/txl/th_polaris91chaincasecover.jpg
 
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