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
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.
Hi James Thanks for the info
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.
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!!!
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.
As Andy says that's a crazy price. John and Jane at sprockets unlimited are a mine of info and will sell you the correct chain for any application.
Sounds like the Po fitted 1/4 to save on weight and width. The advantage is that you can fit O ring chain if it's 1/4", and then equates to the same width as the standard one, but you can't fit O ring on standard commando chain size.
Send the ANIL one back and save money!
It's worth noting that their belts drives come in different ratios and usually gear the bike down compared to the standard primary ratio. It's almost certainly why your bike is revving so high at 60mph. You could count the teeth on the sprockets and work out the ratio and compare it to standard primary ratio.
My Commando has a Norvil drive and 21 tooth gearbox sprocket. It's about the same overall ratio as a standard primary drive with a 19 tooth gearbox sprocket.
Thanks for all your input. Did seem like a lot for the chain I have to say. I was assured that it was right for a 22 tooth sprocket. Might be worth a call back to make sure i didnt order five by mistajke!
I have tried calling Norvil to ask about the belt drive gearing and the head steady but getting to talk to Les is like trying to get an audience with the Pope!