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Chain v primary

Submitted by tony_little on Sat, 21/09/2024
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Heavy Twins

Hi folks, finally decided to join.
Went for a spin on my 57 Dommie 99 and within a few hundred yards got a graunching sound from below.
Limped home and found the rear chain (which needs replacing) was wearing a groove in the inner primary next to the gearbox sprocket. 
Could it be that the knackered (new one ordered) chain is responsible. Everything seems tight, primary, gearbox. so I'm a bit puzzled.

Any thoughts?

Submitted by george_farenden on Sat, 21/09/2024

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Hi Tony,
Did the previous owner 'upgrade' the chain from a 5/8x1/4" (520) to a 5/8x3/8" (530)? If so, then chain contact with the chaincase is difficult to prevent.  Worth checking sprocket width too as a '530' running on a '520' sprocket will make matters even worse . A '530' makes sense on an Atlas or Commando,  less so on the smaller Dommies.
Also check that the rear chaincase securing bracket isn't bent, forcing the case over towards the chain.
Hope that this helps,
George. 

Thanks George, new chain (3/8) on its way, ordered before I saw your comment. I'll measure the knackered chain in a bit to see what it was. If that is the problem I'm surprised that the smaller chain is not listed anywhere as far as I can see.

Submitted by robert_tuck on Sat, 21/09/2024

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Check the spring link ,they can fail but stay attached and drive but foul the metalwork. Been there.Also check wheels are not badly out of line. .

Submitted by ian_soady on Sun, 22/09/2024

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... in there. On my 1952 ES2 I had to fit the spring link with the clip facing inward towards the wheel as it just kissed the primary case otherwise. And agree with previous comments.

Submitted by philip_hannam1 on Sun, 22/09/2024

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Check wheel alignment
Chain Guard
Gearbox Sprocket
Primary Inner position........... There is a top spacer/bolt that the stand spring hangs off and the lower gearbox bolt bracket. The cure might be as simple as a thick washer helping to space things out.
Is there the correct spacer tube that the footrest bar passes through?

Thanks Philip. Now you mention it I did have to realign those tags on the footrest tube, wonder if tightening the realignment was just enough to move the inner in a bit.

Submitted by david_cooper on Tue, 24/09/2024

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Nortons always had 1/4" chains.  Why? Because, as Franks said...a wider chain wasn't necessary.  He was a better designer than most of us...

Just found out that somewhere in the distant past someone has changed the rear sprocket and chain to 5/8 instead of 1/4. So returned the "wrong" chain and ordered a correct rear sprocket which should sort the problem. Once again, thanks guys for the replies and helpful comments.

Submitted by howard_robinson on Thu, 26/09/2024

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Hi Tony - back a good few days ago George suggested that the chain may have been switched to the later wider chain.  From 1964 all the bikes adopted the wider chain from the Atlas and probably later Manxman bikes.  With the increased acceleration afforded by the bigger twins, with a lot more power output, the chain life diminished spectacularly.  The 88SS Model also got the wider chain.  At the same time the rear wheel sprocket got one tooth less (42) so when you order the new sprocket be aware that the overall gearing will decrease from what your used to presently.   Regards, Howard

 



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