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Gearbox sprocket teeth number

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My 750 seems to rev much higher than my previous bikes. 60 mph is about 5500 rpm.It almost feels like I need to change into 5th I have a 19 tooth sprocket and a Norvil belt drive. 

- What is the standard tooth number for 72 759?

- Will upping the tooth count be the solution or does anyone else suspect another issue.

Thanks as ever

Nick

 

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A 19 tooth g/box sprocket is your problem.Try a 22 tooth sprocket. On my Mk 3 850 this changed the 5,000 rpm at 70 mph with a 20 tooth sprocket to 4,000 rpm at 70 mph. Had a '69 Fastback 750 once - can't remember what sprocket it had but won't be much different from the 850s.

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Hi Nick

Just to mention that different chain lengths are required depending on gearbox sprocket size.

Assuming all else is standard - primary and rear sprocket sizes - then afaik the following apply:

19T gearbox sprocket, 98 links rear chain

20/21T gearbox sprocket, 99 links rear chain (i.e. includes a half-link)

22T gearbox sprocket, 100 links rear chain

The INOA Tech Digest (page 2-2) indicates 21T as the maximum for a stock 750. I have read that going too high for the gearbox sprocket count puts additional strain on the gearbox - which makes sense.

I have 21T and 99 links rear on my 750 Roadster which was a big improvement over 19T in keeping the revs down a bit.

Apologies if you are already aware of all this.

Andy

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Hi Andy good point. I have ordered a new chain from Andover. Turns out the PO had fitted a 1/4 inch sprocket and skinny chain??? so going back to standard Andover assure me chain I have ordered will fit the 22T sprocket. Mind you a new chain is 90 quid!!!

N

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Nick

It's obviously up to you but I'd suggest checking with Andover Norton exactly what spec chain you are getting for £90.

I paid just under £50 (incl VAT & delivery) for an IWIS 99 link chain 2 years ago from Sprockets Unlimited. Having a half-link I would expect this to cost more than a chain with an even number of links.

A 100 link Wassell Elite chain is £16 (+ delivery +VAT) from the NOC Shop.  This will be basic chain meeting ISO 10190 although probably not exceeding the standard by much.

IWIS chain has a good reputation.

Andover Norton lists a 102 link IWIS chain at £39.95 (+delivery +VAT). Their part no. 06.5441/102

£90 for two links less (assuming 100 links for 22T) looks a bit steep - unless I'm missing something.

Andy

 

 

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