Cush/sprocket runout

Hi guys. How much runout is considered normal on the rear sprocket? I cant be 100% certain if it's the sprocket or the cush drive itself but there is definitely some run out. The wheel spins true.

The sprocket is larger diameter than the other sprocket I tried so it's more noticeable, but both show some runout.

I have a dial indicator but no good way to set it on the cush drive as the sprocket mating surface isnt a continuous piece.

The wheel is in place and tight. So I would have expected all the slack out of the cush drive to have been taken up.

I would say at the tip of the largest sprocket its maybe 1/16" to 1/8"? Eye balling it. I'll get the dial indicator on it tomorrow when I have time to swap the sprockets.

Thanks!

I wouldn't think your runout would be that much. Is it left-to-right runout or radial runout? In either case, I would check your bearing on that side, then your cush rubbers. Unless the sprocket is warped, I suspect one of them is worn. I've also had sprockets that weren't a tight fit on center, so they needed to be shimmed to center on their hub.

irk miller said:

I wouldn't think your runout would be that much. Is it left-to-right runout or radial runout? In either case, I would check your bearing on that side, then your cush rubbers. Unless the sprocket is warped, I suspect one of them is worn. I've also had sprockets that weren't a tight fit on center, so they needed to be shimmed to center on their hub.

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It is side to side runout.

As part of adapting my 93 wheel onto an 83 bike I put in all new bearings. Everything seems seated fine to me and when tightened up the wheel spins fine.

The cush rubbers were reused but they looked ok, without any cracks. In fact, when reinstalling the cush drive I had to tap it in all the way around to get it to seat as it was a nice tight fit. I took that to be a good sign of the condition of the rubber.

Is there supposed to be zero run out? Or is a little ok? I never checked this before I took the original wheel and sprocket off

I don't think 1/16" is too much runout, but if you had to tap it in to seat, could be that you're not all the way seated. Seems like most parameters are measured in the thousands, or even hundreths, not tenths. So, 1/8" might be a lot, but not necessarily too much. Is there a lock ring or other means of holding the sprocket in it's cush pockets?

irk miller said:

I don't think 1/16" is too much runout, but if you had to tap it in to seat, could be that you're not all the way seated. Seems like most parameters are measured in the thousands, or even hundreths, not tenths. So, 1/8" might be a lot, but not necessarily too much. Is there a lock ring or other means of holding the sprocket in it's cush pockets?

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I found my dial indicator and i set it up to confirm the wheel was true, which it was. Then i found where the high spots were on the cush drive and really beat them in with a hammer and piece of 2x4. Now the runout is 0.6mm or 0.02" ... dont think you can ask for better than that.

Thanks for the advice!

Now put the chain on, tension it, and check the runout.