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Mudshark

Variable chain tension

13 posts in this topic

This is a re-post / update....

I have a "problem" with my '06 XR650R.

The rear sprocket has a "high spot" which cases the chain to have

variable tension.

The chain / sprockets are brand new (3rd new chain) RK GB520GXW

Sprockets are Renthal 15 / 45

I have replaced the chain and sprockets once before, thinking that the old

chain had crappy links and / or the Sprockets were defective... but it

still did it. The problem is that although the runout on the sprocket

is only about 1mm it causes a 5mm difference in chain tension between

the "loose" side and 180degrees later the "tight" side resulting in

"chain slap" this slap is causing the chains to sound real crappy after

less that 2000 miles (hence the third chain in 4000 miles)

This gets expensive.

It does not matter what sprockets I use, so I'm tempted to say that the hub

is defective, but when I checked it, it seems to have no runout etc..

but put a sprocket back on there and the runout re-appears. (at the same location)

There is a tiny (1mm) gap / play around the large raised portion of the hub

that the sprocket fits around and after tightening on the sprocket, the first

bit of torque "repositions" the sprocket off to the one side by a fraction. This

is the only area that I can find any variation, I am taking the bike back to the dealer to have this checked out next week.

BTW the bike is DS'ed and gets used mainly on the road and in not subjected

to what it's designed to endure, so I'm a bit miffed about all this crap...... does anyone have any advice please?

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Would it be possible to shim the "tight side" of the sprocket so when you torque the bolts it can't be pulled off-center? I'm picturing several layers of aluminum can material cut into strips fitted between the sprocket and raised portion of the hub.

I've experience lesser and greater degrees of this problem on most every bike I've owned. I've always just set my chain sag at the tight spot and called it as good as it gets.

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Would it be possible to shim the "tight side" of the sprocket so when you torque the bolts it can't be pulled off-center? I'm picturing several layers of aluminum can material cut into strips fitted between the sprocket and raised portion of the hub.

I've experience lesser and greater degrees of this problem on most every bike I've owned. I've always just set my chain sag at the tight spot and called it as good as it gets.

Thanks for the thoughts HGT..

I've tried the shim thing but it just comes out after about 3 to 500 miles

and setting the tension at the tight spot, well thats what i've been

doing but the "chain slap" gets pretty bad after a few thousand miles and no

amount of chain lube and "correct" tension can stop the rattle it starts to

make.

I'm afraid of 2 things.

1. the CS bearing is going to pack up because of it.

2. I'll break the chain and engine casings etc...

Obviously, in the dirt you don't notice it so much, but commuting to work it

sucks. I don't like folks looking at the bike because the chain makes such

a noise.... they should be looking at it because it's way cool :thumbsup:

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I would guess that the problem isn't the vertical, (in and out), run out, but more likely the sprocket is not concentric with the axle. Have you checked the radial run out as well?

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I am hoping that it is just a typo but, you did write 530 chain intead of 520. A 530 would cause a big problem.

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I would guess that the problem isn't the vertical, (in and out), run out, but more likely the sprocket is not concentric with the axle. Have you checked the radial run out as well?

I agree here, and the problem may be the holes as in mounting holes in the hub, so Id check that concentricity of the sprocket mounting holes...

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lol!! yes a typo on the 530 :ride:

I've check both runouts sideways and concentric both are a tad out.

it's the radial one that worries me the most.

I'll let the dealer take a look at it next week (I'm dropping it off on Saturday)

I hope they are as concerned about it as me :thumbsup:

Thanks for the thoughts so far though.

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you can also try mounting only the sprocket bolts and then check the run out so you can figure if it is the hub or the bolt circle machined out of round.anyways looks like a factory deffect so maybe the warranty may cover it....good luck

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Just in case...try a different chain if you can,maybe your sprocket is o.k. who knows?

3rd chain and 3rd set of sprockets..... done all that.. :applause:

Tonight I put new rubber on the bike, so while I had everything off I did

the bolts only check. One of them is a fraction off... probably within spec about 1mm. It's enough to pull the sprocket 1mm off center

while tightening it down I guess. I'll let them look at it.

I'm also concerned about the rotor, it's easily 3mm off. It "wobbles" while

rotating. That is not in spec :ride: I'm sure they'll replace it.

Thanks for the input.

:thumbsup:

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Update:

1. The warped rotor has been repaired.... didn't know that you could

do that. It is perfectly flat now and looks good.

2. The issue with the chain has not been resolved.

The tech working on the bike struggles with grasping what the

issue is and insists that it is not the hub.

I tried to explain that since the "high" spot is always 180degrees

from the loose spot and that it always occurs on every revolution

of the wheel and is located on the exact same spot on the wheel or

sprocket, that it has to be run-out on the sprocket / hub.

He considered this notion to be so ridiculous that he never even

tested the sprocket for run-out.

3. I also discovered that they / he had let my bike boil over. The

expansion tank was empty and there was dried coolant on the motor.

I have a 1.6 bar cap on that radiator and have commuted in 106 deg

weather for over an hour on this bike regularly and had no boil

over, ever... what that hell was he doing to cause it to cook???

and how hot did it get? I hope that nothing else got damaged??

4. he had also over tightened the chain... insists

that the spec is 3/4" slack.. I had to show him the manual

before he grudgingly accepted that he was wrong.

Needless to say, I’m pretty miffed right now. :thumbsup::applause:

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V.C.T. is normal. :thumbsup:

Yeah I know that..... but not when it's so bad that you cant keep the chain

slack in spec because of it. like 3/4+ inch difference in slack between the

tight and loose spot .... it's crap. makes the chain super slappy and eats

both chains and sprockets in under 2000 miles. (mostly street) ... like I said

it's crap. Ive tried stock, JT and Renthal sprockets. The Renthal offers the

snuggest fit. but still loose enough to cause a 3/4" - difference between

tight and loose spot.

I shimmed up the sprocket now using flat spring steel, it seems to have reduced

it to within acceptable limits :applause:

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