Author Topic: Which gearbox sprocket - how many teeth!  (Read 2226 times)

Offline 900triple

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Which gearbox sprocket - how many teeth!
« on: 06.06. 2011 20:36 »
Hi,

My plunger A7 has a 49T rear sprocket and I need to obtain a replacement gearbox sprocket. I've not run the bike yet (soon I hope...) and I'm looking for a sprocket which will allow reasonable acceleration but more importantly good cruising at 50 - 60mph. Minimum vibration etc.

Does anyone have a suggestions as to what is the most appropriate number of gearbox sprocket teeth?

Cheers

Alan
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Online muskrat

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Re: Which gearbox sprocket - how many teeth!
« Reply #1 on: 06.06. 2011 20:49 »
G'day Alan,
               your rear sprocket is for sidecar work, std solo is 42. So to give the std ratio using that rear you would need a 22 on the g/box, std is 19. Would be a lot easier to replace the rear as the front is a motor out and g/box off job.
Cheers
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Offline a10gf

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Re: Which gearbox sprocket - how many teeth!
« Reply #2 on: 06.06. 2011 21:02 »
Tried a search for 'sprocket teeth' and 'gear sprocket' (examples) ? Lots of hits, stories and ideas.

See http://www.a7a10.net/forum/index.php/topic,1352.0.html on how to make most out of the forum search. I realize there is really lots of info stored in this forum!

My sprocket experiments (a10) http://www.a7a10.net/forum/index.php/topic,165.msg623.html#msg623 , ending up with 20 - 42. Is there anyone supplying non-standard rearsprockets for the plunger?
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Offline 900triple

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Re: Which gearbox sprocket - how many teeth!
« Reply #3 on: 06.06. 2011 22:38 »
G'day Alan,
               your rear sprocket is for sidecar work, std solo is 42. So to give the std ratio using that rear you would need a 22 on the g/box, std is 19. Would be a lot easier to replace the rear as the front is a motor out and g/box off job.
Cheers

I guessed that 49 is for the sidecar but unfortunately thats all I have. I recon its easier and less cost to put a bigger gearbox sprocket on. Luckily the engine and gearbox are both out being rebuilt just now  - so nows the perfect time to do it!

Cheers

Alan
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Online trevinoz

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Re: Which gearbox sprocket - how many teeth!
« Reply #4 on: 06.06. 2011 23:01 »
Shouldn't a plunger A7 have a 46 tooth sprocket?

  Trev.
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Online Brian

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Re: Which gearbox sprocket - how many teeth!
« Reply #5 on: 06.06. 2011 23:04 »
Yes, a plunger A7 should have a 46 T . I have a 19 front and 46 rear on mine and I reckon thats about right.
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Online muskrat

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Re: Which gearbox sprocket - how many teeth!
« Reply #6 on: 07.06. 2011 12:58 »
DOH! Back in the corner I go. Sorry, 46 is correct. Must have been thinking of the S/A.
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Online trevinoz

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Re: Which gearbox sprocket - how many teeth!
« Reply #7 on: 07.06. 2011 22:22 »
And if I'm not mistaken, the short stroke plunger Star Twin has 45.

            Trev.
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Offline RoadRunner

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Re: Which gearbox sprocket - how many teeth!
« Reply #8 on: 10.06. 2011 17:06 »
Opps - my A7 has a 42t rear sprocket (67-6150 which is for an A10?) and no idea what the g/box sprocket is (18 or 19?)! So I'll have to wait and see how it performs.

However the good news is that new sprockets can be purchased from Velcette (The Vincent H.R.D. Company), Merdian Works, Birmingham Road, Allesley, Coventry. CV5 9AZ. Tel 01676 522331. Took a while to come through appears to be good.

RoadRunner
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Offline wilko

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Re: Which gearbox sprocket - how many teeth!
« Reply #9 on: 10.06. 2011 23:29 »
Here in Oz it's quite common to just get your old sprockets rebanded to whatever specs you want and cheaper.
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Online Brian

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Re: Which gearbox sprocket - how many teeth!
« Reply #10 on: 11.06. 2011 00:58 »
Be carefull with that gearing RR, the A7's dont like being overgeared. The reason I ended up with my A7 was the previous owner kept seizing it and couldnt work out why, it had 19/42 gearing and it just put too much load on the engine, hence the seizures.

The A7's like to rev, treat it like you stole it and they go really well.
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Offline RoadRunner

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Re: Which gearbox sprocket - how many teeth!
« Reply #11 on: 11.06. 2011 19:37 »
Oh Sugar! Thanks Brian for the heads up - never ever ridden the beast in 24+ years of ownership; built up from various bikes after being given a frame and logbook. But hopefully in the next few months it'll be running.

Cheers
RR
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Offline RoadRunner

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Re: Which gearbox sprocket - how many teeth!
« Reply #12 on: 21.07. 2011 11:43 »
Hi,
Well, finally got the beast started yesterday and she sounds wonderfully crisp!
But going back to the question of sprockets I've actually got an 18 tooth gearbox sprocket (yes, I guess it should be 19 but being young and .........) and at present the rear is 42 tooth and yes, the bike is not as responsive as it should be.

Hence, if I'm to keep the 18T gearbox sprocket (to save dismantling the engine/g/box) will a 46T rear be okay or do I need a slightly larger one still??

If so any advice on where best to purchase one from in the UK?

More than likely I'll have a new chain and 42T sprocket with new bearing for sale if I have to replace it!

Cheers
RoadRunner
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