Rear Chain Adjustment

Interstate · Mar 13, 2023

Hey all,

I've been looking thru posts on proper rear chain adjustment. It appears there's lots of concerns/techniques to get it right. What I've gathered is that the total cain slop on an unloaded machine on its center stand, measured on the bottom side (top side tight) should measure 1-1/4"+. This assumes parallel rear forks.

Any thoughts? BTW, it's a 1973 850 stock Interstate I've had since '74. Thankx!

robs ss · Mar 13, 2023

If I were you I would always check the tension (up-and-down play of the chain) with you on the bike with no stand. Needs a friend to help.
I use a tape measure, standing vertically, and my target is 3/4" (19mm)
This, for my bike & shocks, equates to 30mm (1 1/4") on the centre stand.
Once you know what the "centre-stand-reading" is for your bike, it's a doddle.
Cheers

Edit: Rider weight can be significant here, so don't take too much weight with your feet.

Interstate · Mar 13, 2023

Thank you!
Also found this link where the rear wheel alignment is made by measuring (L & R sides) from center of axle to center of forward most bolts on the isolastic mounts. Do you feel this is proper?

kommando · Mar 13, 2023

Never done it that way, always with florescent tubes or string aligning to front wheel.

Tornado · Mar 13, 2023

robs ss said:
If I were you I would always check the tension (up-and-down play of the chain) with you on the bike with no stand. Needs a friend to help.
I use a tape measure, standing vertically, and my target is 3/4" (19mm)
This, for my bike & shocks, equates to 30mm (1 1/4") on the centre stand.
Once you know what the "centre-stand-reading" is for your bike, it's a doddle.
Cheers

Edit: Rider weight can be significant here, so don't take too much weight with your feet.

Some member here posted a neat tip for doing this measurement while seated, no helper....take a length of wire or string, loop it around the chain mid-run, then pull it up while having your weight on the seat....measure how much line moves against something handy (seat securing knob etc).

seanalex · Mar 13, 2023

Tornado said:
Some member here posted a neat tip for doing this measurement while seated, no helper....take a length of wire or string, loop it around the chain mid-run, then pull it up while having your weight on the seat....measure how much line moves against something handy (seat securing knob etc).

thats a great idea

robs ss · Mar 13, 2023

seanalex said:
thats a great idea

- especially if you're Nigel-no-friends (no offence @Fast Eddie !)

marshg246 · Mar 13, 2023

Interstate said:
Thank you!
Also found this link where the rear wheel alignment is made by measuring (L & R sides) from center of axle to center of forward most bolts on the isolastic mounts. Do you feel this is proper?

I get it in the ballpark that way. If I have a helper (usually not), I use two boards to align it with the front wheel. Failing that, I remove the chainguard and sight down the chain. Once it's known to be right by any method, then counting turns of the adjuster nuts is all that is needed.

The two boards method is much easier if your rear wheel is wider than your front. On a Norton, since they are usually the same, I have a 1/4" thick board nailed to the edge of each long board where they will touch the rear tire (I use 2x4 for the long boards). You press them against the rear wheel with the bike held upright. When front wheel is straight and the rear wheel is aligned, there will be an equal gap on both sides of the front wheel.

From a Triumph Workshop manual:

Onder · Mar 14, 2023

If you are sitting on the bike when you measure does not that change dramatically when each riders weight is different? The tightest point would be at the centre of the arc of the rising and falling rear wheel. A light
fellow like myself barely compresses the shocks when seated static. Ideally would you not remove the shocks
and then lift the wheel assembly with a jack to mid point and set the chain free play then? Now that adjustment is proper, you reassemble shocks and measure the play whilst on the stand. You now have the correct amount to use, on the stand, forever more.

Mart UK · Mar 14, 2023

I'd have thought the factory recommended setting is such, to take into account any further tightening that can occur at extremes of suspension movement.

Fast Eddie · Mar 14, 2023

Onder said:
If you are sitting on the bike when you measure does not that change dramatically when each riders weight is different? The tightest point would be at the centre of the arc of the rising and falling rear wheel. A light
fellow like myself barely compresses the shocks when seated static. Ideally would you not remove the shocks
and then lift the wheel assembly with a jack to mid point and set the chain free play then? Now that adjustment is proper, you reassemble shocks and measure the play whilst on the stand. You now have the correct amount to use, on the stand, forever more.

Generally speaking, that’s exactly what the factory have already done in order to give the free play recommendations in the manual !

Interstate · Mar 14, 2023

marshg246 said:
I get it in the ballpark that way. If I have a helper (usually not), I use two boards to align it with the front wheel. Failing that, I remove the chainguard and sight down the chain. Once it's known to be right by any method, then counting turns of the adjuster nuts is all that is needed.

The two boards method is much easier if your rear wheel is wider than your front. On a Norton, since they are usually the same, I have a 1/4" thick board nailed to the edge of each long board where they will touch the rear tire (I use 2x4 for the long boards). You press them against the rear wheel with the bike held upright. When front wheel is straight and the rear wheel is aligned, there will be an equal gap on both sides of the front wheel.

From a Triumph Workshop manual:

View attachment 104688

Very good! Simple & precise. I did a similar thing long ago with piece of string nailed taught to a board & align from one side only. I can see my mistake with that method as it would give me the "Wrong" alignment you show in Fig. F1 since I set my alignment from only one side of the machine. Thanks.

ludwig · Mar 14, 2023

marshg246 said:
I get it in the ballpark that way. If I have a helper (usually not), I use two boards to align it with the front wheel. Failing that, I remove the chainguard and sight down the chain. Once it's known to be right by any method, then counting turns of the adjuster nuts is all that is needed.

The two boards method is much easier if your rear wheel is wider than your front. On a Norton, since they are usually the same, I have a 1/4" thick board nailed to the edge of each long board where they will touch the rear tire (I use 2x4 for the long boards). You press them against the rear wheel with the bike held upright. When front wheel is straight and the rear wheel is aligned, there will be an equal gap on both sides of the front wheel.

From a Triumph Workshop manual:

View attachment 104688

OK for a Triumph, but not good enough for a Commando, where the swingarm is fixed in the engine cradle.
This method assumes that the engine cradle and isolastics are perfectly lined out in the frame, which is assuming a lot.
The wheels can be in line, but the bike may still ride like a crab.
I have hollow wheel spindles and a hollow front iso bolt, which helps line out the wheels, but also check that they are in the same vertical plane.
(warped swing arms are not unheard of..)

Once the rear wheel in the correct position, I made these 'little feet' , with holes in 0.5 mm steps:

It positively locks the spindle fore-aft .
Took some time to make, but then I never have to worry about wheel alignment again..

Onder · Mar 16, 2023

Yeah but you are adding weight....

SteveA · Mar 16, 2023

robs ss said:
- especially if you're Nigel-no-friends (no offence @Fast Eddie !)

We have Billy-no-Mates in the UK.... Leaves Nigels out of it!

SteveA · Mar 16, 2023

Interstate said:
Thank you!
Also found this link where the rear wheel alignment is made by measuring (L & R sides) from center of axle to center of forward most bolts on the isolastic mounts. Do you feel this is proper?

Personally I would say no.....or.....

Not until you are 100% sure of basic wheel to wheel alignment. Then base your adjustments on the measurements you take after taking the baseline measurements from the points you identified.

This would mean having stuff written down or 'remembering' the base setting or differential between sides! I don't trust myself not to lose the notes or 'misremember'.

I have a Maxton 'Ronometer'....Aluminium square section device which fitted to the rear wheel and runs forward of the front, set eve gap as other say.

Yes, it's an expensive solution, but it isn't fragile like tubes and not eye watering for race bikes/regular use.

I have used it during bike build up processes to get chain alignment sorted as well. Now supplemented by a cheap laser.

SteveA · Mar 16, 2023

ludwig said:
OK for a Triumph, but not good enough for a Commando, where the swingarm is fixed in the engine cradle.
This method assumes that the engine cradle and isolastics are perfectly lined out in the frame, which is assuming a lot.
The wheels can be in line, but the bike may still ride like a crab.
I have hollow wheel spindles and a hollow front iso bolt, which helps line out the wheels, but also check that they are in the same vertical plane.
(warped swing arms are not unheard of..)

Once the rear wheel in the correct position, I made these 'little feet' , with holes in 0.5 mm steps:

It positively locks the spindle fore-aft .
Took some time to make, but then I never have to worry about wheel alignment again..

Do you have a couple of alternate sets to accommodate the life of the chain? Or gearing changes?

ludwig · Mar 17, 2023

I have a 'follow up' set, but I never get to use them.
The sprocket wears out before the chain ( around 20 000 km) but I change them together.

Rear Chain Adjustment

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