Author Topic: 48 tooth Rear sprocket  (Read 7010 times)

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Offline John F

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48 tooth Rear sprocket
« on: 15 Dec 2005 at 08:16 »
Does anyone have information on where to obtain a 48 tooth rear sproket for my B29 ? As the one on my machine is totally worn out. I have explored the option of having a new sprocket made with the intention of shrinking it on to the brake drum. If anyone out there has completed this excercise before I would welcome any advice.

Offline Chris

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Re: 48 tooth Rear sprocket
« Reply #1 on: 15 Dec 2005 at 12:31 »
Hi John
Before having a new sprocket made, it is worth enquiring whether a standard "plate wheel" is available with 48 teeth to the chain size required. These are very much cheaper than sprockets made to order. These are obtainable from most good transmission specialists. The teeth are hardened but the centre is soft and can be trepanned out to fit the brake drum where it may possibly be shrunk on. I tack welded the sprocket to the drum in one of my retorations. I have used this method successfully on three occasions once on the brake drum and twice in restoration of badly worn sprockets.

Offline Doug

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Re: 48 tooth Rear sprocket
« Reply #2 on: 16 Dec 2005 at 04:02 »
Quote from: Chris
...worth enquiring whether a standard "plate wheel" is available...These are very much cheaper than sprockets made to order.


Quite right, below is an image of a 50 tooth plate sprocket purchased to renew the shrunk-on rear sprocket of my 1936 600cc Douglas.  Besides the shrink fit (and the cast iron drum is serrated to give more ‘grip’) there are three notches to suit corresponding tabs keyed and silver soldered to the drum.  I do not know if the B29 has this feature.  The plate sprocket cost US$22 (and I probably paid too much at that.)  It might be this is what the shop you contacted intend on doing, machining a plate sprocket blank.  It certainly is a lot cheaper than hobbing the sprocket teeth as well.  The plate sprockets available in the USA might be heat treated, but if so then not very hard as the machine freely all over. 


Larger Image

Also make sure that the tooth form suits the size of the rollers on the chain.  If using 5/8” pitch chain you are reasonably safe.  Renold (#11054) 5/8”x1/4” chain uses a Ψ0.400” roller.  The standard available 5/8” pitch chain in the USA is 5/8”x3/8” (Renold also offers the same, #11056), however the roller diameter is still the same Ψ0.400” as the narrower chain.   So all that needs to be done if you have the wider sprocket is to narrow it to suit the 1/4” wide British chain. 

If using a 1/2” pitch chain, you need to be more careful.  Renold still lists two nominal 1/2”x3/16” chains (apparently at one time there were even more!)  The more common (Renold #111046, also known as 415) is 0.192” between the chain plates and uses a Ψ0.305” roller.  The other size (Renold #110044) is 0.205” between the chain plates and Ψ0.335” roller diameter.  Not easy to tell the difference when the components are worn.  It seems Douglas used both at various times between the vintage and veteran eras!  The two standard, readily available 1/2” pitch chains in the USA are #40 and #41 are not equivalent to the two mentioned Renold chains.  But the #41 does use a Ψ0.306” roller (close enough!) and is wider at 1/4”, so the sprocket can be machined narrower to use with the Renold 111046, if ready made plate sprockets are not available. 

Douglas used 1/2”x3/16” on some of the lightweights for a final drive chain, but according to the spares list the B28 and B29 were fitted with the 5/8’x1/4” sprocket, part number 9789, of 47 teeth. 

Reprint of spares list, non-illustrated, is available from John Withers, item VIN212.  See his advert here.

-Doug

Offline John F

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Re: 48 tooth Rear sprocket
« Reply #3 on: 18 Dec 2005 at 08:20 »
Thankyou Doug and Chris
For your prompt repliy to my request for the sprocket replacement on my B29. Doug your information on chain sizes was very enlightning and is probaly the reason why the front sprocket I have has been welded on one side of the teeth only I assume to make it suit the rear sprocket.
I had enquired about a straight sprocket blank, although was a bit concerned it may be to thin and not have enough surface area on the brake hub as the original sprocket had a been manafactured with10mm wide mounting boss, this I assumed would be for ease of location to the hub and have a greater surface area for mounting.
I will be in touch in future with more queries as my restoration progresses.
Regards
John F

Offline Doug

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Re: 48 tooth Rear sprocket
« Reply #4 on: 19 Dec 2005 at 01:40 »
Quote from: John F
...as the original sprocket had a been manafactured with10mm wide mounting boss...
The Aero sprocket is the same way.  Except it is only 5/16" wide where it shrinks onto the brake drum, so I am able to machine it out of the width of the 3/8" plate sprocket.  If you can get by with 9.53mm (3/8") instead of 10mm, you might be able to do the same. 
-Doug

 

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