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Discussion Starter · #1 ·
I've begun to refurb a desmo of dubious history due to a prior owner swapping out components the extent of which I'm not yet sure. I've started with a chain and sprocket replacement. Its my first time working on the sssa and I used some prior threads on guidance on setting eccentric hub position. However, I've run into something I couldn't find any discussion on. When adjusting the eccentric, I could turn it through roughly the 3 to 9 o'clock positions and back, but could not rotate it all the way through. Since I understand the desired position to be between 4 and 5, and I didn't have any problem getting there, that's where I've set my position. I understand that it isn't desirable to set an upper position anyway, and while everything seems fine and test rides have been uneventful, I'm just bothered that it wasn't obvious what was preventing the hub from rotating through. I'd appreciate any feedback on whether this is normal to have only the lower positions or if it might be indicative that I've got a problem I need to look further into. thanks.

 

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I see you have had the tail off. Although I don't have any help to aid in your situation, perhaps you could tell me how easy your pins went back in. Mine is the posting right before yours. Come to think of it, mine only rotated partially as well. I thought that was how they were supposed to be. Did you go to a 520 setup?
 

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grand poobah
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I am no expert but like yourself like to wrench. I have two 748's and my experience is limited to these. I believe You should be able to rotate the hub the full 360. I cannot think of a reason a properly set up hub will not rotate. It is possible the newer 996/8 bikes had some sort of internal limitation to rotation for self protection. From what I know the older ones do not. I recommend you check the following.
The Rear Brake caliper carrier has a slot in it that slides on a stud on the swing-arm. This slot should allow the carrier to move forward and back as the hub is rotated though its arc. If something is blocking the full movement of the carrier on the swing-arm stud it could prevent full rotation of the hub. Ie an aftermarket carrier or maybe a carrier from another series of sswa bikes may be on there, or a wear spot on the carrier that prevents smooth sliding and preventing it from working properly. Please post pics to get more advice here.
Second thing to check. There have been reported cases of the Sprocket carrier cush drives backing out and contacting the swing-arm or hub. At speed this tends to shave off the castle part of the eccentric. In the shop it would probably be enough to limit the movement of the hub.
Next to check is bolt lengths. If you have replaced bolts on the rear rotor, or the sprocket carrier a bolt or head that is too big will catch. However this should have shown up before a test ride. After it will appear as though the aluminum has been machined away.
I recommend you carefully rotate the hub and watch for what is catching. You may have to remove the wheel and or sprocket to get a really good look at the moving parts.
Just for future reference. Setting of the hub to the upper positions will place the lower run of the chain too close to the swing arm and can lead to damage of the underside of the swing-arm. It also dramatically changes geometry/ ride height. Keep us posted of what you find. Best Wishes Brad.
 

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Discussion Starter · #4 ·
I didn't think about taking the photos until after I had reassembled the hub and had the chain on. At that point, I thought, gee it would be really nice to have taken a photo head on of the eccentric when I had the chance, but I wasn't about to disassemble again. Its always the photo you didn't take that bites you in the ...

In response to some earlier question, my seat pins are the plastic ones. I haven't had any issues with them and have had the seat on and off several times. the first time I took it off I hadn't consulted the web and undid the screws to pull the hinge..really bad idea. that was a b to get back on. the pins have been fine.

I had also read about worn cush drives backing out. I put on a 520 chain with fbf quick change carrier so even though I didn't change the cush drives I shouldnt have the back out issue even if they separate.

My look at the exploded view of the eccentric in the parts manual also led me to believe it should rotate through. I was wondering if it was maybe catching on the brake caliper but couldn't confirm it, though since I was working solo I didn't have the best look. I've been out on it several time since the change and everything seems fine so methinks I don't have an inherent problem. I'll have a closer look next time I get it apart. Thanks for the responses.
 

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Discussion Starter · #5 ·
hey neuroduc, I just noticed your location. I've done a few shop visits to a machine shop in your area several times over the last year. small world.
 

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The rear brake caliper and mount will stop the hub from rotating 360 degrees. The problem you will have is if you take the brake parts off first and then accidentally get the hub into the upper part of the rotation. Then when you put the brake back on you will be stuck in the upper segment. If you dont catch this you will tighten your chain and be totally in the upper section and you will snap your chain as it will rub into the swingarm. I watched my buddy do this exact thing this summer...
 

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Discussion Starter · #8 ·
Thanks superfly. Thats good info. I knew I needed to be in the bottom, but was just trying to understand what was stopping me from rotating through. You've explained it.
 

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The rear brake caliper and mount will stop the hub from rotating 360 degrees. The problem you will have is if you take the brake parts off first and then accidentally get the hub into the upper part of the rotation. Then when you put the brake back on you will be stuck in the upper segment. If you dont catch this you will tighten your chain and be totally in the upper section and you will snap your chain as it will rub into the swingarm. I watched my buddy do this exact thing this summer...
?? Moving axle position from 'upside' to 'downside' is possible anytime, or maybe you meant something else?
 
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