The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Frame => Topic started by: tomtit on 27.03. 2014 02:11
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Counted the teeth on the rear sprocket and there are 52. According to everything I read there should be 42T for solo and 49T sidecar on a 1950 Plunger. I'm hoping one of you guru's can shed some light on this. Gearbox sprocket has 20T.
Tom
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Is it possible to have a B25 hub on a plunger, because I saw a 52T sprocket ring for a B25 on vintage-motorcycle.com
Richard L.
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Stock final drive ratio for a plunger A is 19: 42 (1:2.21), with a19/48 (1:2.53), 19/49 (1:2.58), and what you have is close behind at 1:2.6, if you going solo, the way I see it, she'd be peakin' out goin' nowhere- but climb tall buildings ok...??
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Thanks Richard and Dutch, just to add to the mix I counted the chain links and there are 105 links so looks like the chain is for sidecar (104) plus an extra link for good measure.
Looking at the parts list on Draganfly they have a 20T G/box sprocket as "Optional" for a plunger, what would a 20T and 42T combo be like ?.
Thanks again for the info Dutch, haven't a clue in regards to ratios etc.
Tom
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'S ok Tom, just did it on the phone calculator, have considered a 20T front also, which would give 1:2.1
Chain for 19/42 requires 100 pitches/rollers/50 links depending on the lingo you use(this was debated a while back)
Richard- dunno 'bout the B25..?
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Looking at the parts list on Draganfly they have a 20T G/box sprocket as "Optional" for a plunger, what would a 20T and 42T combo be like ?.
So, that's a 20T gearbox sprocket, not cush drive, right? From my thinking, if on the gearbox, it will give you a better range in 3rd and make your sweet cruising spot in 4th at a higher speed. Those ranges are caclulable, but you can't ride arithmetic. The opposite if it's the cush drive (at least on a swing-arm). However, I don't have that setup, so it will be nice to hear from someone who has done it. I have some names in mind.
Richard L.
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With gearing like that it must have been used in trials or scrambles.
A picture of the hub/sprocket would help.
Cheers
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The hub may have come off a B40 also as when I Googled it it came up as fitted on B25/B40. Looks like I have to get me a 42T hub, checked Draganfly but they would have to order in, there are a couple of used ones on fleabay but would rather new or if second hand from someone who's not going to rip me off with a lemon also need a new chain as the old one is knackered.
I'm attaching some photos Muskrat as requested.
Tom
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There was a guy in Victoria selling Renolds chains for Plunger on ebay $85 (?) last year, Musky (I think) posted that.
I bought one, but haven't needed it yet
Did a quick search, but couldn't find it- maybe have a go??
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Thanks Dutch, found the link which was put on by Brian. The guy is selling the chains for $93+$13.50 post which is good for a Renolds so have just bought one.
Thanks again for the heads up, now to find a rear sprocket without having to sell any body parts. *problem*
Tom
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G'day Tom.
Having a look at the 2nd picture I can see what look like scotch keys or welds where the sprocket has been attached to the drum. I do similar with the rear sprocket on my A10 cafe and my A65. I turn off the teeth down to a diameter then buy a cheap sprocket and turn the guts out to the same diameter and weld (on the A65) or scotch key (on the cafe (alloy sprocket onto steel center)) to the old center/drum. A fraction of the cost of a new or good s/hand one.
Cheers
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Ok Tom, and sorry guys respectively, I knew it was one o' yez southerners... *smile*
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i've asked an engineer to do a very similar job to do for my b31 rigid hub which I have little option to refurb as they are very rare hubs, its 7 inch but machining a 42 tooth sprocket to suit the hub would result in a very thin ring of teeth with no strength of its own so would need welding or brazing on most if not all the circumference with consequent risk of distorting the hub, so me and my and the engineers guess was it would be best to use a 46 tooth blank not a 42 tooth one, and fit a bigger engine sprocket to compensate.
Am I doing the right thing by fitting a sprocket with 46 teeth?
Maybe thats why the pics show a 52 tooth sprocket?
Muscrat, do you manage to keep to standard gearing and use a 42 tooth blank when doing this hub refurb job?
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Yes see here http://www.a7a10.net/forum/index.php?topic=1975.msg12668#msg12668
The brake drum type like my '51 has 46 teeth and would be doable.
Cheers
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thanks muscrat I will certainly give the refurb method a go when my 56 A10 (ariel hubs) needs its sprocket replacing.....
The O.D. of the b31 rear drum is 181mm though, so I think welding the new sprocket on might be the only option, and maybe only TIG at that, to keep the distortion down, but I will let the engineer decide once I supply the 46 tooth sprocket to him.
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It would only need a good tack in 4 spots each side. Mine handles the A65's power done that way.
Cheers
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well I just ordered the 46 tooth blank sprocket from cycletreads.co.nz for the princely sum of 44nzd, I'll tell the engineer how you've done it muscrat and hopefully be able to post pics of the finished job in due course.
I guess depending on your location it might be cheaper to buy a new hub complete with sprocket for the crinkle hub wheels but in my case where the sprocket/drum/hub is effectively one piece (riveted together) refurbing with a new sprocket is pretty much the only option anyway.
Whilst this is an A10 thread here is a pic of the b31 hub - basically a cheaper version of the A10 hub but with 520 size sprocket, I did consider trying to adapt the plunger wheel onto the rigid b31 but whilst it is the same width the sprocket and rim alignment is wrong for the b31, and it would also need a custom axle made up.