Rear wheel & chain clearance question

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Hi,

I am finishing up a rebuild of a '72 commando that was provided to me in boxes, so I have never seen the bike assembled.

An issue I am having is that with the rear wheel installed, the chain rubs the outside of the chain guard, even when the wheel is tight in the frame.

The bearings were never pulled from the hub as they were in great shape, and the other pieces appear to be assembled in the correct order according to the diagrams on andover norton and old britts websites.

I have noticed a 4-5mm gap between the back of the sprocket/brake drum and the wheel hub - I replaced the cush drive rubbers and am curious if this is just not fully seated. I have gone to town with a breaker bar on the axle nuts and the rubbing improves, but the quick link still catches the guard and I am sure I am severely over-tightening the axle.

Any hints or suggestions would be greatly appreciated. The only other comment is that I have to spread the rear end slightly to get the spacer on the outside of the speedo drive to fit, which is part of the reason I think the brake drum is not fully seated.

Thanks,
Chris
 
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If you have the standard 19" rear wheel, no way it should be rubbing the chainguard. It's either waaaaayyy out of line with the front or something was assembled in the wrong order. The Titanic has a small gap between the brake drum and wheel hub, but new cushes can make things a little tight. Commandos are also known for imperfect rear wheel to rear fender alignment, so don't let that throw you off. There should be a fairly equal gap between the tire and both sides of the swingarm.
 

MichaelB

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Mine is extremely tight also.
If it’s just the master link hitting you can turn it around so the clip is on the inside.
Or, go to a riveted master.
 
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I have always used the joining link clip on the tyre side with my Dommie, the dreaded pressed steel primary chain case doesn't give enough clearance. A very old friend also does it on his 850 MK2 A.
 

maylar

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Problem with that is that the master link pins can (probably will) hit the gearbox case.
 
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Never happened in 42 years, but the gearbox sprocket did come loose on the lock washer and caused me and it to wobble ! A few aluminium shavings but still knocking up the miles
 
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Check that the bolt used to mount the rear shock (and slot in chainguard) has a thin head. If not, it can force the chainguard in. Nut should be on the outside.
 
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illf8ed

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Hi,

I am finishing up a rebuild of a '72 commando that was provided to me in boxes, so I have never seen the bike assembled.

An issue I am having is that with the rear wheel installed, the chain rubs the outside of the chain guard, even when the wheel is tight in the frame.

The bearings were never pulled from the hub as they were in great shape, and the other pieces appear to be assembled in the correct order according to the diagrams on andover norton and old britts websites.

I have noticed a 4-5mm gap between the back of the sprocket/brake drum and the wheel hub - I replaced the cush drive rubbers and am curious if this is just not fully seated. I have gone to town with a breaker bar on the axle nuts and the rubbing improves, but the quick link still catches the guard and I am sure I am severely over-tightening the axle.

Any hints or suggestions would be greatly appreciated. The only other comment is that I have to spread the rear end slightly to get the spacer on the outside of the speedo drive to fit, which is part of the reason I think the brake drum is not fully seated.

Thanks,
Chris
Hi Chris,

My '72 also has the very close fit from chain to the outer part of the chainguard. The chain has hit the rear of the guard and left a mark. Your situation is not unique. I suppose you could add another shim on the dummy axle and that would move the drum/sprocket toward the timing side. The shim goes on the axle just inside the drum after you take the brake shoe cover off.
 

Tornado

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I believe there were some responses in another similar thread regarding the mounting point on the guard needing some squeezing to a thinner spacing so that chain could clear. Also be sure the thin head bolt is being used to the inside of swingarm such that it slides easily into the guard mounting. Note there are two different lower shock mount bolts, one is thin headed for chainguard my 850 had these swapped when I got bike without a guard
 

motorson

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Everybody here is talking about the rear wheel and that is where Chris said the problem was showing up. I have also measured a tenth of an inch difference in the offset of front sprockets. In other words, if your chain is hitting the transmission or primary case it could be the offset of the front sprocket causing the problem.
 

Tornado

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Everybody here is talking about the rear wheel and that is where Chris said the problem was showing up. I have also measured a tenth of an inch difference in the offset of front sprockets. In other words, if your chain is hitting the transmission or primary case it could be the offset of the front sprocket causing the problem.
OP stated chain was hitting the outside of the chain guard, not primary.
 

motorson

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"OP stated chain was hitting the outside of the chain guard, not primary."
Yes, but a couple of mentions were also made of chains hitting either the primary or transmission. (I cannot, for the life of me, figure out how everyone is doing those nice little quotes of previous posts.)
 

Tornado

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. (I cannot, for the life of me, figure out how everyone is doing those nice little quotes of previous posts.)
Just use the Reply button lower right of the actual message you want to quote. Text entry should open with that message content already in quote tags.
 
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Just use the Reply button lower right of the actual message you want to quote. Text entry should open with that message content already in quote tags.
Thanks Tornado. I have just learned what to do with the reply to quotes.

Both my 750 and 850 have close clearenes between the chain and outer chain guard edge. Just the way it is.

If you use IWIS 10b chain, it should not hit the inner primary and especially with the clip on the wheel side. 530 chain is unnecessarily wider and can hit the primary. IWIS chains also last a lot longer than any other chains.

Dereck
 
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What I've found is you need to have the 'oil outlet' for the chain oiler, or suitable spacer, in place with the through bolt. Without it, I've found the chain guard twists and you're apt to have the master link hit the very rear edge of the chain gaurd.
 

Tornado

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Regarding that chain oiler fixing point on swing arm,is there anything placed on the SA hump so that the chain doesn't slap against it when flaps up and down? Modern bike has rubber piece along SA where the may slide along it.
 
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Regarding that chain oiler fixing point on swing arm,is there anything placed on the SA hump so that the chain doesn't slap against it when flaps up and down? Modern bike has rubber piece along SA where the may slide along it.
If there is, I haven't seen it. I suspect you could mock something up.
 

MichaelB

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Saw a post on here somewhere that referred to a washer/shim between the drum and backing plate.
Part #21 on rear wheel page. The original parts manuel refers the quantity AR, as required. This was obviously an issue from the beginning. Tore mine down, sure enough, no washer.
I will order some on my next order, in the mean time, anyone know the dimensions of this washer, specifically the thickness.
Part #06.7607, old number NM5276. Must not be anything to technical as it's referred to as a 'washer', not a shim..
 
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My chain guard was damaged by the chain hitting it on the outside when the newly fitted bearings in the brake drum moved. The circlip had not seated correctly and this allows the whole assembly to move. It might be the reason you have a gap on the other side of the brake drum. I had to slim down the circlip to ensure that it properly seated.
 
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