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Out of center rear sprocket (!)

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Mojave

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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.

nc700x stock sprocket.jpg

nc700x JT sprocket.jpg
 
Sorry.......not buying .020" runout is causing any problem on a stamped steel sprocket.........they are just not that precise by design.

I will agree you changed the chain tension during the swap and it is also possible the chain has loose and tight spots as it rotates which could cause a noise or slight vibration..........especially if the chain was too tight to start with.
 
well, that was nicely patronizing

The JT is very precisely made - I measured less than 0.001" runout of the tooth circle to the hub circle. If this is stamped then it is either milled or broached very well. Perhaps you have some wisdom why JT would make them so very nice if it's not necessary. Just what do you know about how a chain interacts with a sprocket, enlighten us will you? I believe this sprocket has a pitch diameter that is too small and also effectively varies. In other words, it was manufactured poorly, and behaves somewhat like a very worn sprocket, except that it isn't very worn yet.

The undulating noise IS GONE. I noticed this noise a few rides after I bought the bike, about 3000 miles ago. A very distinct vibration with the bike IS GONE. This noise and vibration have been there through about 4 wheel removals, 2 different chains, and 10 chain tension adjustments.The new chain is a DID VX with 2,000 miles, with the JT it doesn't snatch now with the bike on the stand. When I put the axle back on the chain was almost too tight to let the axle through - the pitch diameter is clearly larger on the JT than the stock.

The evidence is the stock sprocket, at least mine, is a piece of junk. It works, but not well.
 
Looks out of center to me, compare the worn shoulders @ the 6 o'clock to the 12 o'clock, good idea on shimming that new sprocket or is that how it is always done? I'm going to check mine when I get home this morning. Do you think it was mounted wrong or was made that oblong to began with.
 
OK, the whole story. When I got the bike it had 5K on it. After about 1000 miles I experimented with the gearing by getting a JT 46T alloy sprocket and a new VX chain. I did think there was some added smoothness with this change but I wasn't all that familiar with the bike yet, and with the lower gearing I was running the engine in a higher RPM range all of the time. Above 4200 or so my bike was pretty smooth. I decided I liked the stock gearing more so I took two links off the VX chain and put the stock sprocket back on. This sprocket looked completely unworn. I then took it on a 1000 mile ride that had lots of 30-50 MPH riding and I became very aware of the undulating noise. With that brand new chain I naturally had to adjust the chain a couple times as it settled in. Since that long ride I did another 1000 miles in day rides and my curiosity about the noise grew. I finally put it up on the centerstand and it became clear what was causing the noise. For this post I didn't really want to explain all that.

Conventional wisdom is you change everything at once. Certainly when sprockets are visibly worn you wouldn't want to put a new expensive chain on, or vice versa with an old kinky chain. I'm kind of skating on thin ice here by mixing new and slightly abused components. In hindsight, I wished I had purchased the 43T JT earlier instead of subjecting my new VX chain to that misshapen-ed Honda sprocket. But I think the new combination is fine. Running the bike on the centerstand the chain is "flowing", not snatching up and down like it was with the stock sprocket. It seems pretty quiet, like the rollers are meshing in the sprocket teeth properly. Certainly on the road there is a pretty distinct difference.

I started riding in 1968, and back then Japanese bikes (at least) used cheap and crude final drive components. Chains and sprockets wore out pretty fast, and whatever sweetness the bike had started slipping away after a few thousand miles. When I put new chain and sprockets on, the bikes would be transformed - maybe not quite like new, but so much better I wished I had done the change earlier. With the rise of sportbikes in the 70's and 80's the chain and sprockets got A LOT better. O-rings, much better metal technology, and just as important, better geometry. These factors made smooth final drives that lasted for 10's of thousands of miles on 100+HP 150 MPH bikes.

My stock rear sprocket is a sample of one, and I'm totally not impressed with it. Something like that might have a place on a cheap Chinese 250 but not on a full size Honda. On this forum I've read many posts about odd seemingly random noises and vibrations. I'm not suggesting all of them are caused by the rear sprocket, for example my bike has a noticeable clutch vibration and noise also. But, the two big quirks my bike had were just cured by the the sprocket change (not a simple chain tension adjustment, sheesh).

The diametric clearance of both the sprockets to the hub is about 0.009". That means the runout from assembly could be that high. I took the precaution of centering the sprocket with 0.004 brass shims before tightening the nuts. This might be perceived as unnecessary but it only took a minute to do. A feeler gauge with careful tightening of the nuts could be used for this also.

I took a good look at the JT alloy 46T, and it has the same nice precision as the steel JT 43. I don't like alloy sprockets because of my dirtbike experience - they simply wear out too fast. I didn't really have a choice in my gearing experiment. But after a few hundred miles it looks just barely "burnished" in the teeth roller areas.
 
You have presented a great case...........and have no doubt the JT is of better quality than the stock sprocket. You have a made a better case for replacing the sprocket when you replaced the chain???? Root cause can be very elusive especially when there are dozens of variables..........my original comment was .020" is not much on a stamped piece. But also there is the stacking of all parts tolerances that add up and that is very hard to quantify and qualify from an owners position.

All chains are noisy and vibrate that's the argument for an expensive shaft drive which has a whole another set of compromises.

10 chain adjustments..............many of us have done one or two in 5000-10,000 miles..........some report no need to just the chain in these mileage ranges. Remember........ Too tight is the death to chain, sprockets and bearings.
 
I had the wheel on and off for tire changes and sprocket changes. I usually didn't keep the chain adjusters locked up so I had to adjust my chain tension after mounting the wheel. So the ten adjustments kind of reflect all that, not that I was adjusting the chain every 300 miles or so.

When I got the bike I adjusted the chain a couple times - probably because of the significant change in tension due to the out of centerness. I know I know, you look for the tightest place, but I may not have done that. Still I'm pretty particular about chain tension, I set a little on the loose side myself. Usually there is some tension where the transmission seems happiest shifting and I try to maintain that. My experience with new chains, even the most premium, is two or three minor adjustments before they settle into that long stability. I figure a little chain "stretch", whatever that is, but mostly burnishing of the teeth that simply increases the clearances a little.

Looking at the stock sprocket, there's no doubt it was stamped out of sheet, not laser or waterjet cut. But this stamped "blank" was then taken through several machining processes - one side is undercut by facing, and the hub interface by turning. The holes were drilled. I just took a caliper to the undercut rim, and it has the runout I see in the teeth roots. So there is a lack of registration between these operations. I think the blank was held by the bolt circle for the teeth finishing process, possibly on a fixture with undersize bolts, and then ... some other way for turning the hub. Basically, the manufacturing process wasn't correct. If I was making this I would make the hub hole first then use it as the reference for all the other operations.
 
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Your investigations and conclusions might explain the mystery throbbing vibration that affected some DCT bikes when they first came out.
Mike
 
I experienced this exact problem, and did the same correction, (replacing the rear sprocket), on my 2007 Suzuki DL650.
It really quieted down the phaeton noises from the drive train. I could always hear the noise from other DL650's when passing, or being passed by them.
 
This is why Honda was able to sell the bike for $6999. U.S., got mine a left over for $6500. Corners had to be cut to sell at low price. If I paid $15,000. for a bike, I would demand quality parts throughout. The little things like sprockets, grips, levers can be upgraded for low investment. As long as the engine, electronics and various bearings and suspension parts are of good quality I'll be happy.
 
SergeantChuck said:
I had to look both those words up. I'm not going to lie. If I had to guess I'd say you teach English to Japanese. I'm probably wrong though.
Click to expand...

I'm a truck driver, but you have to promise never to repeat that where my mother might hear it. She thinks I have a respectable job, playing piano in a whorehouse.
 
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