Variable chain tension


12 replies to this topic
  • Mudshark

Posted August 22, 2006 - 06:54 PM

#1

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?

  • HawkGT

Posted August 22, 2006 - 07:31 PM

#2

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.

  • Mudshark

Posted August 22, 2006 - 09:06 PM

#3

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:

  • ghoti

Posted August 23, 2006 - 04:56 AM

#4

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?

  • BWB63

Posted August 23, 2006 - 05:03 AM

#5

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.

  • SniperTeamBravo

Posted August 23, 2006 - 07:52 AM

#6

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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  • Mudshark

Posted August 23, 2006 - 03:52 PM

#7

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.

  • motomonte

Posted August 23, 2006 - 05:57 PM

#8

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

  • motomonte

Posted August 24, 2006 - 03:01 AM

#9

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

  • Mudshark

Posted August 24, 2006 - 08:11 PM

#10

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:

  • Mudshark

Posted August 30, 2006 - 06:28 PM

#11

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:

  • Max Power

Posted August 30, 2006 - 06:42 PM

#12

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

  • Mudshark

Posted September 01, 2006 - 05:17 PM

#13

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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