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gearbox sprockets

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in the process of stripping things down to fit a new gearbox sprocket to my mk3 850 interstate , one fitted is a 23 tooth , is this standard and should I stick with this size or perhaps change as I see there are a few alternate sizes available 

 

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22T was standard and that was only done to lower the revs for noise and emissions. I'd go 21T for everyday use, 20T if you just want get-up-and-go and aren't too bothered about pulling high revs on long motorway trips.

According to the workshop manual, at 7,000 RPM, 20T gives 113mph and 21T gives 119mph. A standard Mk3 will have trouble revving out on 21T.

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My MK3 850 had a 20T g/box sprocket fitted when bought from the Kenya police who wanted the acceleration - changed to a 22T to reduce revs at cruise speed and which provides the best balance for my money.

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If you have had no issues with a 23 then stick with it, if you need more acceleration the drop 1 or 2 teeth but your revs at high cruising speeds will be higher.

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I know they're coming up on a half-century but these are sports bikes, not diesels. They're supposed to rev. At 80mph with a 20T sprocket the engine's spinning at 5,000rpm. It'll do that all day, not that I've seen a Commando cruising at 80 in a long while.

IMO tall gearing is hard on the gearbox - which is the weakest part of these bikes. The loading on the gearbox is higher in general with a large sprocket but, in particular, it's a bigger lever on the sleeve gear hastening all the problems in that area. And getting into top sooner can only be a good thing as it unloads the box.

 


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