Mojave
New Member
As I've gotten used to my bike I started to notice an odd noise - a undulating schess-schess-schess. It seemed to come from the front of the bike and was there if I coasted with the clutch pulled in. It definitely varied with speed and seemed to be front wheel related. But not the brake it seemed since applying the brake made no difference. Hanging to the side I couldn't really heard anything from the chain area. Anyway, I finally put the bike up on the centerstand, started it up and put it in second gear. The chain was pretty snatchy. Looking at the rear sprocket it was obviously "running out", that is the chain circle is not centered on the wheel hub!
I ordered a 43 tooth JT steel sprocket off of ebay - $36 shipped. When I got it I measured the hub to tooth root distance with my 6 inch calipers - it was dead even. Tonight I removed the stock sprocket and measured it - the total runout is 0.02 inches, which doesn't sound like much but seems to cause trouble. I mounted the new sprocket and even shimmed it to perfectly center it on the hub.
On the test ride the undulating noise is gone, and it is, in fact, much quieter. The surprising other difference is a minor but kind of annoying vibration that would happen in the 3700-3900 rpm range is completely absent. I would feel this through the pegs in 5th and 6th gear, and tended to adjust speed below or above it. Now it's gone, and the bike generally seems smoother and quieter on the highway.
One strange thing I found was the JT definitely has a larger pitch diameter than the stock! I had to move the axle up a bit, say .06", to restore the proper chain tension. Considering the out of centerness of the stock sprocke I'm pretty sure it also doesn't have the correct pitch diameter. The links would be "crowded" and floating somewhat above perfect contact. When I take the wheel off again I'll compared the JT to the stock for this diameter.
If you are having odd vibrations or noises I recommend checking or just replacing your rear sprocket. The stock sprocket - at least mine - is a noname POJ, I suppose from a cheap China source. So use a quality JT. Below are a couple of pictures of the stock sprocket and the new (black) sprocket.
I ordered a 43 tooth JT steel sprocket off of ebay - $36 shipped. When I got it I measured the hub to tooth root distance with my 6 inch calipers - it was dead even. Tonight I removed the stock sprocket and measured it - the total runout is 0.02 inches, which doesn't sound like much but seems to cause trouble. I mounted the new sprocket and even shimmed it to perfectly center it on the hub.
On the test ride the undulating noise is gone, and it is, in fact, much quieter. The surprising other difference is a minor but kind of annoying vibration that would happen in the 3700-3900 rpm range is completely absent. I would feel this through the pegs in 5th and 6th gear, and tended to adjust speed below or above it. Now it's gone, and the bike generally seems smoother and quieter on the highway.
One strange thing I found was the JT definitely has a larger pitch diameter than the stock! I had to move the axle up a bit, say .06", to restore the proper chain tension. Considering the out of centerness of the stock sprocke I'm pretty sure it also doesn't have the correct pitch diameter. The links would be "crowded" and floating somewhat above perfect contact. When I take the wheel off again I'll compared the JT to the stock for this diameter.
If you are having odd vibrations or noises I recommend checking or just replacing your rear sprocket. The stock sprocket - at least mine - is a noname POJ, I suppose from a cheap China source. So use a quality JT. Below are a couple of pictures of the stock sprocket and the new (black) sprocket.