Uneven Wear on Countershaft Sprocket

[Mythos]

I pulled the stock countershaft sprocket off my 08 and noticed it had wear all the way around on the side that faces the motor. The side that faces out doesn't look like it was touched by the chain at all.

I had this kind of wear on the rear sprocket of my other bike but the front had no side wear on either side. I can see how a misaligned axle will cause side wear to the rear sprocket but it seems like the countershaft sprocket should be aligned to the chain more or less automatically. The countershaft sprocket drives the chain. Alignment of the countershaft sprocket should stay perpendicular to the countershaft. The countershaft sprocket is a lot smaller than the rear sprocket too which would seem to reduce side wear a lot even if the sprockets were misaligned.

The rear sprocket has no side wear on either side. If the sprockets were misaligned, why no side wear on the rear sprocket?

The method I have used to align the sprockets is to first turn the axle adjuster bolts all the way in. Then I counted the number of rotations it took to adjust the chain to the proper tension and both sides were turned the same number of rotations. After the initial adjustment, I turned the adjuster bolt on each side the same amount each time I adjusted chain tension. Seems to have worked for the rear sprocket but I have this groove worn on the inside of the front sprocket. It's only about .25 mm but it doesn't seem like it should be there at all.

Is the OEM sprocket not flat on the inside? Swing arm bent on one side so the chain is cocked? Any thoughts?

 

[HayaWakened]

I know next-to-nothing about this prob, but can't help but wonder if it's related to the sprocket's position on the countershaft. I can't remember how the fr sprockets fits up on the shaft, and whether there's room for movement.

Just thinking out loud here ...

 

[Mythos]

Interesting thought. As far as I know, the sprocket cant move out of perpendicular to the shaft. There is a spacer between the nut and the sprocket but if the nut is tight, that sprocket should stay true to the shaft.

 

[Mythos]

could it be one link had thinner rollers than the rest and the side plate of that one link was the only one that was wearing the sprocket on the side?

 

[HayaWakened]

Interesting thought. As far as I know, the sprocket cant move out of perpendicular to the shaft. There is a spacer between the nut and the sprocket but if the nut is tight, that sprocket should stay true to the shaft.

Yes, that's what I was thinking, but I'm guessing there'd be larger, more apparent probs if this were the case

could it be one link had thinner rollers than the rest and the side plate of that one link was the only one that was wearing the sprocket on the side?

As in a defective chain? How would just one link (or rollers) make such consistent markings over all teeth on the sprocket as in the pic?

 

[Mythos]

As in a defective chain? How would just one link (or rollers) make such consistent markings over all teeth on the sprocket as in the pic?

As explained by an old mechanic on my other forum, the rear sprocket has 43 teeth, the front has 18 teeth and the chain has 120 links...they all go around in the same direction but the same tooth doesn't engage the same link every revolution of the entire chain. That would only happen if both sprockets had the same number of teeth and the chain had the same number of links as either of the sprockets. Then I suppose the sprockets would have their teeth engaged like gears. After X turns of the sprockets ( it might be 18 x 43 = X ), the same links will end up on the same teeth. This is why I always mark a link to the tooth it was on on the rear sprocket any time I remove the rear wheel. If the pattern of the chain running with the sprockets isn't changed, the wear pattern will unchanged. In the discussion we had, there was a lot of conjecture as to how much difference disrupting the pattern would make but why not keep the pattern the same? So this is how one mishapen link could effect all the teeth on the front sprocket. ..but then I would expect it would wear the rear sprocket in the same way. Only my front sprocket was effected.

 

[HayaWakened]

As explained by an old mechanic on my other forum, the rear sprocket has 43 teeth, the front has 18 teeth and the chain has 120 links...they all go around in the same direction but the same tooth doesn't engage the same link every revolution of the entire chain. That would only happen if both sprockets had the same number of teeth and the chain had the same number of links as either of the sprockets. Then I suppose the sprockets would have their teeth engaged like gears. After X turns of the sprockets ( it might be 18 x 43 = X ), the same links will end up on the same teeth. This is why I always mark a link to the tooth it was on on the rear sprocket any time I remove the rear wheel. If the pattern of the chain running with the sprockets isn't changed, the wear pattern will unchanged. In the discussion we had, there was a lot of conjecture as to how much difference disrupting the pattern would make but why not keep the pattern the same? So this is how one mishapen link could effect all the teeth on the front sprocket. ..but then I would expect it would wear the rear sprocket in the same way. Only my front sprocket was effected.

+1
But am now curiouser. Looking forward to your findings & solutions

 

[JeffSyh]

I'd suspect cush drives or maybe the rear wheel isn't perfectly even on both adjustors? I use a caliper over the marks to make sure they are exact same when adjusting the chain. I know my vortex front sprocket has a front and back and you have install it one way but the oem I'm not sure? I'll have to take a look at my old oem one when I get home.

 

[Mythos]

@JeffSyh I put a Vortex coiuntershaft sprocket on my ZX-14 last year and I didn't know there was a right and wrong side out. I put it on so the logo was facing out. I hope that was the right side out...I can't remember if there was a logo on both sides.

The cush drive was worn TF out for a long time. It was a little loose the first time I took the rear wheel off to change tires and the second time I took the wheel off, the sprocket carrier could have just fell out. I replaced them with Sensei dampers just a thousand miles ago. That might be it. I tried measuring the adjuster bolts with a calipers when I initially adjusted the chain but the equal threading on both sides should be as accurate. The bolts have the same number of threads/centimeter.

 

[202mphbusa]

Rear wheel misaligned? For a while

 

[JeffSyh]

Yes logo facing out. Here is a picture of Mt oem it looks like it wore a bit more on the inside then the outside.

 

[Mythos]

Rear wheel misaligned? For a while

Maybe but not for the last few thousand miles. ...unless my method of turning the bolts out the same number of turns is wrong. I'd say mine were like this from day 1 by the looks of the outside of the teeth. I don't think there's any wear there.

Thank you for the pics @JeffSyh ! I'd rather have a little wear in both sides like yours has but it's reassuring to see something a little similar happening on another busa. You can actually see a point every two teeth on mine where the side plates engaged. I'm guessing you were not using stock 18/43 sprocket gearing with your OEM sprocket.

 

[JeffSyh]

It was 100% stock front and rear with stock chain, it's a gen 1 so 17/40 stock? I'm 16 and 42 now though.

 

[Mythos]

Very interesting @JeffSyh. So you had a combination of odd/even teeth on your sprockets too. My gearing was 18/43. The reason I asked was because the shape the chain's inner plates carved into mine is very definite. The chain has to advance several teeth on the front as it turns around the larger diameter of the rear but apparently, with 18/43 gearing, it's always the same pairs of countershaft sprocket teeth that end up getting occupied by chain links. You can very clearly see the point of unworn metal on my sprocket between where the inner plates of the chain engaged.

I was having a conversation with @RedBull recently where he was explaining that the wear pattern of a combination of odd/even compared to odd/odd or or even/even is different. I don't know for sure if this is what he meant but it must be preferable to have some side wear on both sides of the sprocket like yours.

 

[Mythos]

With wear this irregular, I think I will have another measure with my calipers of those adjuster bolts. Maybe I screwed up when I was counting the turns. I'm pretty sure I remember trying to measure and it was difficult to squarely fit the caliper points between the front of the adjuster slot and the front of the axle block. What method do you use to adjust your axle squarely, @JeffSyh ?

 

[JeffSyh]

I actually didn't notice yours skips a tooth on wear... that's super odd as if it groved in over time and now skips over to find its "home" so to speak. Was your chain always adjusted properly and free rolling? I assume yes. I adjust my chain for the proper allowed slack (I'd have to read my service manual again for exact measurements) on the driver side than I adjust my passenger side with a caliper measuring the same as driver side on the axle slide plate to the rear of swing arm and double check slack as it sometimes gets tighter after adjusting the pass side. I double check both measurements and than take it for a good ride then double check again chains and sprockets aren't cheap... my cush drives were totally fine when I upgraded mine so I'm not sure what wore cush drives would do but I'm sure you'd loose slack in the chain on hard pulls and possibly have a bit of wobble in the rear sprocket. I can send pictures if my chains adjustment procedure doesn't make sense (it's over kill anyways). Oem sprockets are rubber inners also so maybe the sprocket was just not built completely straight.

 

[Mythos]

@JeffSyh the chain has been pretty loose a coule of times. I don't think it was ever terribly tight but I used to adjust it at minimum specced slack when the cush drive was loose. I could feel the slop in the sprocket carrier when I rode the bike with the dampers worn out. I'll try measuring with a calipers as you do. If the rear sprocket tilted from the cush drive being wore out, I think that woud wear the outside of the front sprocket and mine was worn on the inside.

I'll have a look at it. Maybe it's time I invest in one of those chain adjusting tools that fit in the axle and the swing arm pivot on both sides or else the laser one. There's some good suggections on this thread:

My cheapazz red neck method of chain adjustment. | General Bike Related Topics

I just use two threaded rods one in the axle one in the swing arm pivot. It's not because I think the Gillis chain adjusters are inaccurate, it's just easier to do standing up. I can easily get to within less than one MM using a standard tape measure. it'd not my idea I just wasn't willing to...

www.hayabusa.org

 

[Mythos]

@JeffSyh
I checked the axle alignment using a calipers. It was getting dark and I wasn’t as completely anal as I usually am but I was pretty careful to get the calipers level with the bolt. I measure both the length of the bolt including locknut and the length from the front of the axle block to the back of the swing arm.

Here’s what I got:

Front of Axle Block to back of swing arm
RH 62.20 mm
LH 61.90 mm


Difference: 0.3 mm.



Adjuster bolts including locknut
RH 31.59 mm
LH 30.87 mm


Difference: 0.72 mm





Based on the measurements of the adjuster bolts, I’d say it’s possible I was off by a half turn when counting the number of rotations on each. That doesn’t seem like it could have caused the sort of wear that happened to my countershaft sprocket. Also, whatever was causing the sprocket to wear as such was happening right up to the time I removed the sprocket. The wear marks are shiny and clean which I would not expect if there had been a problem in the past which was corrected by new cush drive rubbers.

I'ts possible my sprocket carrier isn't seated all the way into the hub. I pressed it in and there was still a gap between the hub and the carrier. I'm pretty sure after tightening the axle, the carrier was flush to the top surface of the hub. I'll have to double check that.