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Correct method for measuring chain slack?

16K views 29 replies 11 participants last post by  rmb 
#1 ·
What I've done in the past is measure the chain slack while on a rear stand. Someone mentioned a while back about pushing the chain down for the start and pushing it up for the stop measurement. I didn't know that at first. Now, I'm being told to measure on the side stand.


So, what is the FINAL ANSWER on this subject. I really hope this doesn't turn out to be a 50 page "best oil" thread.


1. do you measure on the side stand or not, if not, what measurement do you use (1 3/8" is stock)?

2. do you push the chain down AND then push the chain up to get a measurement?

3. does your chain hit the bottom of the swing arm when taking the measurement?
 
#2 ·
The chain needs some slack so it doesn't get pulled over-tight when the swing arm is flat and the chain is at full extension. So that's what you're trying to judge - how much is enough slack not to pull it screaming tight.

Weight on the bike is a good idea, to flatten the swingarm out - the flatter it is the less slack you have to leave [at that point]. Sit all your weight on it and get someone to flip the chain with their toe - does it still have some space to move?

I'd be surprised if you had to leave so much slack that the chain could be pushed up to touch the bottom of the swingarm.
 
#5 ·
1. do you measure on the side stand or not, if not, what measurement do you use (1 3/8" is stock)?

I measure on a rear stand. Mainly because that is where it is easiest to adjust and align. Doesn't mean it's right, but has worked well for me. I try to set it in the middle of the range (35mm).

2. do you push the chain down AND then push the chain up to get a measurement?

Yes

3. does your chain hit the bottom of the swing arm when taking the measurement?

Almost
 
#6 ·
1.
Always on the centre stand or race stand, never on the lean stand.
Always on a warm, cleaned and lubed chain.
I make a point of making sure it's never tighter than mid range, target mid range, and if a wee bit slacker than mid range, it's OK.

2
Yes, as it's Total Slack not just Droop Slack that make up the required measurement.

3
No.
 
#7 ·
A
A clarification to 3 above.
While the chain does not touch the swingarm with top slack, it does touch the rubber guide/protector.

B
I just did a garage check to get a sense of how much the chain slack changed by taking the bike off the centre stand, with the bike fully on its wheels, and not even on the lean (side) stand.
There was no apparent difference.
Also keep in mind that the 919s lean stand results in fairly significant lean angle, with the lean stand foot transferring quite a bit of weight to the ground.

C
Doing chain adjustment on a lean stand is at best a flawed method.
Just because a 919 only comes factory fitted with a lean stand, and has no swing arm spools, does NOT at all mean that lean stand adjusting is required, good or best.
It merely means that within the confines of just having a lean stand, use the lean stand to adjust the chain.
Finally, the 919 Owners and Service Manuals, as well as the Common Service Manual are all remiss by not even mentioning tight spot(s) checking, nor the difference in slack that occurs between warm and cold for dirty chains lubed with very high viscous lubricants.
 
#11 ·
We're heading towards going in circles here.
I just did another test, and by sense of feel think there is actually more rear wheel weight on a race stand to ground, than there is rear wheel weight to ground when on the lean stand.
Supporting this is the fact that my tall set up only needs a bit of a tug on the bars to get the rear wheel to lift off the ground and pivot on the lean stand foot.
IF one only has the lean stand to work with, then what choice is there?
None, plus being stuck with all the aggravation of checking for tight spots and not being able to do spin checks.
IF one has a centre stand, use it, and use the same factory range of adjustment, and enjoy all the advantages it offers for cleaning, inspecting, setting and checking - as compared to using the lean stand.
IF one has a race stand, use it, and use the same factory range of adjustment, and enjoy all the advantages it offers for cleaning, inspecting, setting and checking - as compared to using the lean stand.
Attempting to lean the bike up against a wall or other support in an effort to mimic the bike being up straight on its own with all the weight on just the wheels, is begging for disaster and offers zero advantage.
 
#13 · (Edited)
Step one: put it on the center stand or rear stand
Step two: wiggle the chain
Step three: decide if its too loose or tight based on the wiggle test
Step four: adjust
Step five: start over

Basically what I'm trying to say is that it's really not as minute as a lot of people make it out to be... as long as you're close you'll be fine... And I'd usually err on the side of too loose than too tight.
 
#21 ·
There are as many ways to align the rear wheel as there are mechanics who do it. Here's mine, perfected over 60 years of riding, and a decade of racing. Once proficient it usually takes only five minutes, and does not require any special tools.

Preliminary alignment:

1: Set the slack as you want it, concentrating on the chain side primarily. Just try to set the brake side close, but don't get obsessive about it.

2: On a center stand of any sort (OEM, Phobstand, swingarm stand, a floor jack on the left with a block of wood under the side stand, or hang it from the rafters. It doesn't make a difference using this procedure as long as the rear tire is off the ground and the bike is stable and as level as possible.)

All adjustments in the following procedures will not significantly affect the chain slack you have already set as only the right adjuster is moved.

3: Spin the rear wheel backwards to keep the upper run of the chain tensioned and listen to the chain as it runs over the rear sprocket. If it is noisy slow the spin and look at the centering of the chain on the sprocket. If it's contacting the rearmost teeth of the sprocket on the inside the wheel is angled to the left. To adjust turn the right side adjuster to move the axle rearward a small amount, and spin the wheel until the chain gets quieter.

Conversely, if it is contacting the rearmost teeth on the outside of the sprocket the wheel is angled to the right. To adjust turn the right adjuster to move the axle forward too far, then while holding on to the frame kick the wheel forward (Do this carefully! Don't want to knock it off the stand!) to seat it against the adjuster. Now turn the right adjuster to bring the axle back, again spinning the wheel occasionally until it gets quiet and looks centered on the sprocket. Keep at it, invariably needing a kick forward if you overshoot, until it is as quiet as you can get it. Frankly, sound trumps centered. I have had a chain that was visibly centered on the sprocket, but was noisier than when it was biased to the inside. Left it there. I think it was a slightly out of line top guide.

4: Tighten the axle enough to cinch everything down, start the engine and run up the wheel while dragging the rear brake to stabilize the chain. It should make about the same noise level as it did while spinning by hand, just a higher pitch. If not, have someone take a short video of it that you can look at in order to determine which way it needs to go.

Torque the axle, clean up, and take a test ride. Done.

Rob

A P.S. for those amongst us who occasionally push the safety limits. I witnessed an incident where a mechanic decided that adjusting while the wheel is under power by using a long extension that would keep his hands away from the wheel is a better idea, and it worked for a short time until in a split second of inattention he let the socket come off the adjuster whereupon the extension pivoted into the wheel, caught a spoke, and was thrown into his right side chest. Fortunately he was using a 3/8ths breaker handle to turn it which prevented the extension from penetrating his chest, but it broke four ribs and not only punctured his lung, but actually lacerated it. It was touch and go for a day in the ER, but he did recover in only five months.

'nuff said.
 
#22 ·
There are as many ways to align the rear wheel as there are mechanics who do it. Here's mine, perfected over 60 years of riding, and a decade of racing. Once proficient it usually takes only five minutes, and does not require any special tools.

Preliminary alignment:

1: Set the slack as you want it, concentrating on the chain side primarily. Just try to set the brake side close, but don't get obsessive about it.

2: On a center stand of any sort (OEM, Phobstand, swingarm stand, a floor jack on the left with a block of wood under the side stand, or hang it from the rafters. It doesn't make a difference using this procedure as long as the rear tire is off the ground and the bike is stable and as level as possible.)

All adjustments in the following procedures will not significantly affect the chain slack you have already set as only the right adjuster is moved.

3: Spin the rear wheel backwards to keep the upper run of the chain tensioned and listen to the chain as it runs over the rear sprocket. If it is noisy slow the spin and look at the centering of the chain on the sprocket. If it's contacting the rearmost teeth of the sprocket on the inside the wheel is angled to the left. To adjust turn the right side adjuster to move the axle rearward a small amount, and spin the wheel until the chain gets quieter.

Conversely, if it is contacting the rearmost teeth on the outside of the sprocket the wheel is angled to the right. To adjust turn the right adjuster to move the axle forward too far, then while holding on to the frame kick the wheel forward (Do this carefully! Don't want to knock it off the stand!) to seat it against the adjuster. Now turn the right adjuster to bring the axle back, again spinning the wheel occasionally until it gets quiet and looks centered on the sprocket. Keep at it, invariably needing a kick forward if you overshoot, until it is as quiet as you can get it. Frankly, sound trumps centered. I have had a chain that was visibly centered on the sprocket, but was noisier than when it was biased to the inside. Left it there. I think it was a slightly out of line top guide.

4: Tighten the axle enough to cinch everything down, start the engine and run up the wheel while dragging the rear brake to stabilize the chain. It should make about the same noise level as it did while spinning by hand, just a higher pitch. If not, have someone take a short video of it that you can look at in order to determine which way it needs to go.

Torque the axle, clean up, and take a test ride. Done.

Rob

'nuff said.
I have been adjusting like this for a while. I'm sure I learned from Rob here on WT. Thanks Rob! :thumbup1:
 
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