Author Topic: A7 sprocket size  (Read 1634 times)

Offline mrshells

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A7 sprocket size
« on: 27.01. 2009 22:11 »
Whats the largest front sprocket that can be fitted to a A7 Star Twin
mine previously was registered as a side car outfit and I think is geared for pulling a lot of wheight as first gear is a waste of time.and it pulls all the way to max revs with no problem
so i need to fit a bigger sprocket
Never realised what a hassle it would be to change it !!!
its all stripped down for a coat of paint any way but I wouldnt like to have to just change a sprocket !!!

Online bsa-bill

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Re: A7 sprocket size
« Reply #1 on: 28.01. 2009 10:17 »
others will comment but I think the general way to gear for a sidecar was to change the gearbox sprocket.

All the best - Bill
All the best - Bill
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Offline a10gf

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Re: A7 sprocket size
« Reply #2 on: 28.01. 2009 15:59 »
Hi, a few sprocket comments here : http://www.a7a10.net/BSA/2002tour.htm

Check the number of tooth you've got and maybe 1 or 2 up will be fine. As it's quite some work to change them, try getting some input from other A7 owners to get it right first time.

I have never heard about rear sprocket alternatives for the plunger, but they may exsist. The gearbox sprocket is available in different sizes.


e

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Offline trevinoz

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Re: A7 sprocket size
« Reply #3 on: 28.01. 2009 20:18 »
Gents, I think you will find Plunger/Rigid bikes used a 49 tooth rear sprocket for sidecar work, all others being the same as solo.
  Trev.

Offline mrshells

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Re: A7 sprocket size
« Reply #4 on: 28.01. 2009 23:38 »
th rear cant be changed i dont think
it looks like part of the brake drum
i need to find out if i can get maybe a 20 tooth for the front

Online olev

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Re: A7 sprocket size
« Reply #5 on: 29.01. 2009 10:12 »
I'm pretty sure the gearing on my 52 star twin is standard.
Engine sprocket - 27 teeth
Clutch - 54 teeth
Gearbox sprocket - 18 teeth
Rear hub - 45 teeth

In top gear (1:1) using Tombeau's tyre (66.5 cm dia) and the above gearing, my calculations give about 15.6 mph/1000 revs.
This gives about 3850 rpm at 60 mph or 100 kph.

At 10000 rpm that calculates to more than 150 mph. woo hoo what a rocket.
cheers

Offline trevinoz

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Re: A7 sprocket size
« Reply #6 on: 29.01. 2009 20:59 »
Olev's gearing is correct.
The rear sprocket/brake drum is one piece. If you have a 49 tooth rear sprocket, a 20 tooth gearbox sprocket will be fairly close to correct gearing for a solo.
  Trev.