Author Topic: Excentric rear sprocket?  (Read 1875 times)

Offline roadrocket

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Excentric rear sprocket?
« on: 20.04. 2008 13:03 »
Hello fellow A10-ers

The bike finally has come out from hibernation, and started first kick after 5 months, with fresh oil (I know, should have been done before lay up, but would have drained down anyway). After the ride home from the winter storage on old petrol, which didn't burn very nicely, i gave it the inaugural clean and oil changes, and took it for a proper ride with new petrol, which was much better. Now, my bike has always had a bit of a pogo stick front end, and i have always thought it to be the ffront wheel that was out of true, but now I measured it again, and I have about 1 mm out of round, and about the same sideways - not much I think. Then I went on to check the rear chain tension after the ride, and noticed it was dead tight. Strange. But then I checked the tension all the way through a full revolution, and found a lot of slack most of the way, only to be followed by a length of absolute tension. How come? The obvious explanation is that the rear sprocket is excentric, but I couldn't measure this just by placing a pointer near the edge of the sprocket - and yes I did check the wheel was aligned in the frame. Have any of you experienced this? Other possible reason for this to occur? I am running on the old, original sprocket, and it could do with replacement, but I am looking for a change from full width spongy cable operation to half width rod operation, so would not like to buy a new sprocket that hopefully only will see limited future use. But this much uneven wear? Is that a known thing?

Otto in Denmark
Otto in Denmark

Offline Beezageezauk

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Re: Excentric rear sprocket?
« Reply #1 on: 20.04. 2008 15:00 »
Hi Otto,

I have come across this once before and I couldn't understand what the problem was.  It turned out that the chain was stretched in one place but not in another.  There was nothing wrong with the sprocket.

To prove it I removed the chain and laid it lengthways (with rollers vertical) on a sheet of polythene to keep it clean.  I then bent the chain in an arc to one side as far as it would go and could see that the radius of the arc varied at different places.

I don't know what caused it to happen but I replaced the chain with a new one and everything was OK.

Beezageezauk.

Offline a10gf

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Re: Excentric rear sprocket?
« Reply #2 on: 20.04. 2008 16:18 »
Have had same uneven chain problem, varied from absolutely tight to very slack as the wheel was turned. Found some tolerable middleway-adjustment and continued using it for while before replacing, but it could wear sprockets.

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Online groily

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Re: Excentric rear sprocket?
« Reply #3 on: 20.04. 2008 18:19 »
Tight spots in chains are pretty common . . . nothing to worry about and nothing to do with the shape or state of the sprocket. Hibernation may have made it worse, but I suspect the symptoms were there when the old lady was put to sleep for the winter. You can adjust the chain so that there is at least some slack at the tight spot - try to ensure there is slack when sitting on the thing off the centre stand, as the difference between 'on the stand' and loaded with rider can be a lot. However, the chain's dead and should be replaced. Not replacing will wear both sprockets, and possibly the sleeve gear to which the gearbox final drive sprocket is attached as well, which is a pain. Chain is cheaper than the other bits, and a lot easier to replace. Groily
Bill

Offline dpaddock

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Re: Excentric rear sprocket?
« Reply #4 on: 20.04. 2008 20:20 »
Check first that the sprockets are not the problem:
     Get the chain on its tight spot, then mark the rear sprocket with a chalk mark. Rotate the wheel one revolution and see it the chain goes tight again. If it doesn't, go to the gearbox sprocket and do the same thing but this time reaching in from the off side and marking a tooth crest with a dab of white paint.

Then check the chain as noted. And beware of replacing sprockets using old chain and vice versa.

David
'57 Spitfire


Offline roadrocket

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Re: Excentric rear sprocket?
« Reply #5 on: 21.04. 2008 20:18 »
Thanks folks!

I didn't think of the chain as the culprit, and wouldn't have thought it possible. It is not a cheap one either, but a real Renold. Will buy a new chain and destroy it (evenly) with the old sprocket  ;)

Otto in Denmark

Offline snowbeard

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Re: Excentric rear sprocket?
« Reply #6 on: 13.05. 2008 20:18 »
well, sounds like you found it, but I thought I'd add that I saw the same thing when my master link had worn and crushed both rollers and wallowed out the plates adjacent to it.  you might be able to replace a few links if you have the extras left over?

I just got a newer chain, since finding new links was next to impossible.
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Offline roadrocket

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Re: Excentric rear sprocket?
« Reply #7 on: 13.05. 2008 21:17 »
Yes, I now have a Japanese chain on  *conf* , but the dealer said she fitted it to her own bikes, so I thought the OE item better be let having a break, and then I hope they have bettered themselves when this one has worn out. Yes thats right; lady classic bike dealer! Rides Velo Viper.
Otto in Denmark

Offline fido

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Re: Excentric rear sprocket?
« Reply #8 on: 14.05. 2008 02:02 »
There is no problem with using Japanese chain on your BSA as the japanese still use imperial size chain on their bikes. The only problem you tend to get is with O ring or X ring chains, as the overall width is greater and there is not always enough clearance.

Offline a10gf

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Re: Excentric rear sprocket?
« Reply #9 on: 14.05. 2008 11:52 »
Fido wrote:
Quote
and there is not always enough clearance.
Yes, I have experienced that. And a chain that touches something can (in additiion to grinding down stuff) be damaged in the link 'rivets', and then easily break. Had to drop the idea of o-ring on my A10 pl.

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