Author Topic: A larger gearbox sprocket?  (Read 2371 times)

Online Greybeard

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A larger gearbox sprocket?
« on: 06.05. 2015 13:36 »
Yo Dudes!
My Plunger A10 seems under geared; she pulls away like a train but at about 55 I'd really like to have another gear, by 60MPH I feel I'm straining the old girl. She has 18 gearbox teeth and 42 rear wheel teeth which I believe is standard. I see that Draganfly offer larger gearbox sprockets at 19, 20 & 21 teeth. I am not using modern lower profile tyres. What opinions or experience do you have of changing the gearbox sprocket to make a longer legged drive ratio?

Offline duTch

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Re: A larger gearbox sprocket?
« Reply #1 on: 06.05. 2015 14:53 »
 Isn't 19T standard...? Even at that I've also thought to go up a tooth, engine sprocket might be better, but I think they only come in one size- unless one was to muck around and adapt one
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
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Offline a10gf

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Re: A larger gearbox sprocket?
« Reply #2 on: 06.05. 2015 15:13 »
Quote
Isn't 19T standard...?
Believe so too.

Quote from my a10 plunger webpage, testing some sprockets. My opinion, 21 not nice in town, needed lots of clutch (= lots of clutch wear).
Quote
was happy with 21 for highways, but 20 seems like a better compromise acceleration\relaxed 4th gear rpm.

Got a 21 somewhere, giveaway to anyone who wants it (and confirm it's no good in practical use :O)

18 must be good for the daily wheelies show down the neighbourhood :O)

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Online Greybeard

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Re: A larger gearbox sprocket?
« Reply #3 on: 06.05. 2015 15:36 »
Quote
Isn't 19T standard...?
Believe so too.

Quote from my a10 plunger webpage, testing some sprockets. My opinion, 21 not nice in town, needed lots of clutch (= lots of clutch wear).
Quote
was happy with 21 for highways, but 20 seems like a better compromise acceleration\relaxed 4th gear rpm.

Got a 21 somewhere, giveaway to anyone who wants it (and confirm it's no good in practical use :O)

18 must be good for the daily wheelies show down the neighbourhood :O)

A long time ago I once dropped the clutch a bit sharply and lifted the front wheel off the ground! Though that may have been before I changed the sidecar ratio rear sprocket that was on the machine when I got it. Perhaps the 18 tooth gearbox sprocket is also for a sidecar.

I've just been having a read of part of your travel notes; fascinating!  *good3*

Offline RichardL

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Re: A larger gearbox sprocket?
« Reply #4 on: 06.05. 2015 16:36 »
According to Bacon, no 18/42 combination offered stock in any model or year and no 20 or 21 tooth gears available back then. I guess those came later as aftermarket pieces. It seems to me that your bike must have been 19/42 originally and someone changed to the 18, or, if your sidecar rear was 49, Bacon shows "A7ST s/c" with 18/49 for 1949-1954, which might explain something if your bike started life as an A7. BSA might have just dragged the gear ratios along without making it a matter of record that they also applied to A10's, as well.

For the most part, in all of Bacon's books, I think he just recites from the records without adding special information. Kind'a like me, right now...and, no, I am not a librarian in real life or on TV, but I am just reading from the books.

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Online cyclobutch

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Re: A larger gearbox sprocket?
« Reply #5 on: 06.05. 2015 16:46 »
18" or 19" wheels?
Various, including ...
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Online Greybeard

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Re: A larger gearbox sprocket?
« Reply #6 on: 06.05. 2015 16:48 »

Online Topdad

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Re: A larger gearbox sprocket?
« Reply #7 on: 06.05. 2015 16:50 »
My s/w arm model was the same , changed to a 21 and the bike seems happy enough with it will pull nicely even 2 up so some cog on the plungers different . greybeard I'd look at changing but first check all the other sprockets and take it from there, Bob
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Re: A larger gearbox sprocket?
« Reply #8 on: 06.05. 2015 16:54 »
Thanks TopDad Bob,
I await further illumination from the Forum Elders.  *respect*

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Re: A larger gearbox sprocket?
« Reply #9 on: 06.05. 2015 16:56 »
What time is it in Oz???  *smile*
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Re: A larger gearbox sprocket?
« Reply #10 on: 06.05. 2015 17:08 »
What time is it in Oz???  *smile*

Changing the gearbox sprocket is not a job I'm looking forward to so I can wait a while. Does the gearbox have to come off to do this job on a plunger engine or can I remove the clutch, strip out the gearbox in situ and change the sprocket?  *dunno2*

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Re: A larger gearbox sprocket?
« Reply #11 on: 06.05. 2015 22:45 »
From memory you can 't  change the gear box drive sprocket on a plunger engine  ,think you can still do the internals . From distant memory g/box casing held by 4studs To engine and sprocket is on the wrong side ie between g/box end and primary inner moulded to d/side crankcase. But more likely due to that to be other cogs don 't you think?  Can't wait to hear what is right? Bob
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Offline duTch

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Re: A larger gearbox sprocket?
« Reply #12 on: 06.05. 2015 23:18 »


 From memory *conf*, I think you need to pull the whole unit, then split 'em....that's why I carved a hole behind my clutch and fitted a plate from same as A65/50 and Trihards- haven't utilized it much yet but bound to soon...

 Geez GrayB., given the speedo drive is upstream from the final drive, you wouldn't even be doing 55/60mph with an 18T...  *eek* probably 56.842105...with 60mph reading- mines the other way 'cos of ummatched speedo/18"x4.00 tyre with 2.040 rolling circumference.

 I feel the same of mine with  the 19T, but've been meaning to ask what anyone who uses a 20T reckons, thought it may be a bit tall...maybe not so, might stock up.

 
Quote
What time is it in Oz???  *smile*
...=   GMT +10hr.. *????*

 Bob rounded me up there- got sidetracked measuring wheel...but what he said, except not sure what you mean Bob?
Quote
But more likely due to that to be other cogs don 't you think
...
 
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
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Online KiwiGF

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Re: A larger gearbox sprocket?
« Reply #13 on: 07.05. 2015 01:10 »
On my 56 swing arm GF I went up one tooth on the engine sprocket, with the rest standard, that seems to be optimum for my riding, and for the NZ national limit of 100 kph, going up two teeth according to a mate with similar bike is not so good for hills etc as it causes much more changing down to 3rd. Speedo is of course unaffected by changing the engine sprocket.

I have slightly more power than std (I hope....) as I have flat top pistons and 356 cam.

You might want to keep your gearbox sprocket as it is and just change your engine sprocket by say 2 teeth, as it's less work?
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Online Greybeard

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Re: A larger gearbox sprocket?
« Reply #14 on: 07.05. 2015 09:32 »
...You might want to keep your gearbox sprocket as it is and just change your engine sprocket by say 2 teeth, as it's less work?

Sounds like a plan. I'll investigate engine sprockets.