Sprocket Teeth Selection 25 or 27 ?

Clutches, Chain & Belt Drives

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DieselCrazy1
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Sprocket Teeth Selection 25 or 27 ?

Post by DieselCrazy1 » Thu Oct 29, 2009 7:43 pm

Hi Everyone
Anyone has any suggestions of using 25 teeth engine sprocket or 27 teeth engine sprocket and advantages and disadvantages of using them with 4 speed gearbox


thanks

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Re: Sprocket Teeth Selection 25 or 27 ?

Post by Sphere » Thu Oct 29, 2009 8:25 pm

I took a 25t duplex for the primary and decided I would play with the secondary ratio on the gearbox axle. So, I have a Bullet 350 donor, which sports a 16t. I will likely change it to 19 or 20t. This makes the primary drive uncomplicated, just use what is already there, no need to think about altering chain tensioner in the primary case and what not.
'92 Enfield + Hatz 1B40: street legal, weld up stainless exhaust, check engine rpm and change final drive sprocket.

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Re: Sprocket Teeth Selection 25 or 27 ?

Post by oldbmw » Tue Nov 03, 2009 1:15 pm

I cant answer you question directly.
the engine sprocket size is immaterial as it will always be in the same place relative to the crank at the firing pulse.
However you want a clutch/engine sprocket ratio that does not easily divide. You are limited to what is available though. Also the number of links in the chain should not divide easily into either the front or clutch sprocket teeth. This is best achieved by having three different prime numbers in all cases. Failing a prime number an odd number usually helps. The reason for this is to even out the wear on the chain and the clutch sprocket. It can make 4-5 times the difference in a worst case design to chain life. Rear chains are not so critical as the relationships change every time you change gear or use the clutch.
Another non obvious concern is the Enfield Gearbox seems to absorb power based on the rpms of its input shaft rather than by the actual power transmitted. For this reason keeping the clutch ( gearbox input shaft) rpms as low as is reasonable can help conserve power.
For practical reasons ( emergency spares) I would run with the original Enfield primary setup if possible (even though it is no where near optimal) and adjust the final drive ratio by changing gearbox and if necessary rear sprockets.
Larry

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Re: Sprocket Teeth Selection 25 or 27 ?

Post by DieselCrazy1 » Thu Nov 05, 2009 6:50 pm

Thanks that information helps alot
I really love this site alot of valued information is exchanged
Thanks again

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