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Dave

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MAGNETOS BTH Douglas E 29

Started by Foppoli Matteo, 26 Apr 2017 at 18:24

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Foppoli Matteo

Hello Friend, I came across this megnetos BTH For my Douglas E29
But the gear is too small, do you know the number of teeth?
Every information is appreciated
Thanks  Matteo

cardan


Hi Matteo,

If the magneto is to run at half engine speed, the gear on the magneto will have 2x the number of teeth on the gear on the crank.

Cheers

Leon

Foppoli Matteo

Hello thank you your kind reply i suppose 50 teeth confirm?
another question! How does the dynamo work? It lacks caliber gear in my engine?
Thanks matteo

cardan


Yes 50 teeth - same as the cam wheel.

Leon

Doug

Matteo,

There is a conical slip-clutch inside the magneto gear. An extension shaft with a gear attached plugs into the end of the magneto gear, and drives a small pinion on the dynamo. This provided the increase in speed to spin the dynamo fast enough, while the slip-clutch protects it from rapid acceleration/deceleration.

This is the one I made for my 1928 F28. The conical clutch is actually from a 350 EW, to which I shrunk on a larger 50 tooth gear to suit the F28. The dynamo drive gear is aluminum.



Here it is with the extension shaft removed.



As is often the case, after I made one, I found an original extension shaft.





I think the extension shaft, gear, and pinion are the same as the 350 EW. The magneto gear is different because the 350cc has less teeth than the 600, but the components of the clutch are the same. As mentioned, you can alter the magneto gear by machining to suit the 600 or the 350cc engine. If you cannot find the extension shaft and gear, I do have engineering drawings.

This is s section view of the clutch and extension shaft assembly.



The dynamo drive gear has 40 teeth and the dynamo pinion has 14 teeth.

-Doug




Foppoli Matteo

Thanks to Doug for clarifying the operation of the Dinamo, you got the gears?
Magnet and dynamo drive?
You can tell me if a Dynamo of a Douglas 1931 model E31 is the same as my E29 bike

Thanks to Matteo

Doug

Matteo,

No, I do not have gears for sale. The photos are of parts to my bike. I did make a drawing of the extension shaft and gear, if you eventually have to machine one.

-Doug

Foppoli Matteo

Hello, Doug,  please send  engineering drawings.
the gears are module 1 ?

http://www.atti.it/a/003174_pignone-modulo-1-in-acciaio-c45-numero-denti-z-050

thanks Matteo

Doug

Matteo,

The gears are 18 diametral pitch, and not based on the Modual (metric) system. The only thing metric on a Douglas that I can think of are the ball bearings, and even some of those are in Imperial (inch) sizes. The pressure angle is 20 degrees, near as I can measure. Generally I have been told that at that time 14.5 degrees was the preferred pressure angle, but I have found the opposite to be the case. You do not want to mix 18 diametral pitch gears cut to 20 and 14.5 degrees pressure angle together. 

PM me an email address that I can use to send the PDF files of the drawings to.

The BTH PA Form C dynamo used on the T6/S5/S6 machines is different to that used on both earlier and later Douglases. The drive on the S6 is shorter and uses the gear as a coupling.



The drive on the 350/600 EW and the later models in the mid-thiries has an elongated snout. BTH PA From B. This is the type you should look for:



Besides the 350EW & 600EW, E/F28, E/F29; it was used on the A31 and derivatives, K/M32, and the 250/350/500/ and 600cc Aero models.

The full post on the BTH PA series dyno is here:
https://www.douglasmotorcycles.net/index.php?topic=2461.msg8898#msg8898

-Doug

-Doug