Author Topic: Magneto differences  (Read 5525 times)

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Offline alexd912

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Magneto differences
« on: 29 May 2010 at 13:57 »
Hi all,

I recently came across some magnetos and im hoping they will fit my G31.

There appears to be some differences to the main cog and I was hoping for some enlightenment.

The design on my bike just has a plan toothed cog (see pic of engine) and the other magnetos have a spring and a separate part to them (see pics with 2 mags side by side).

Im just wondering what is the spring and plate for on the pictures with the 2 magnetos?

Also Im on the look out for the toothed gear that drives the camshaft as my one is missing a tooth...


Regards

Alex




« Last Edit: 31 May 2010 at 10:27 by Dave »
Best regards
Alex
1930 Douglas G31

Offline eddie

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Re: Magneto differences
« Reply #1 on: 29 May 2010 at 17:55 »
Alex,
         I think you will find that the other 2 mags are from earlier machines that had a pancake dynamo fitted. The pinions incorporate a clutch to prevent overloading the drive.
         Be warned - there may be 2 options for the camshaft pinion you need. Some OHV engines had cams with 6 splines and others had 8 splines - also, the major diameter of the splined part is smaller on the 8 spline type.
                                  Regards,
                                          Eddie.

Offline Doug

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Re: Magneto differences
« Reply #2 on: 29 May 2010 at 20:01 »
Alex,

As Eddie says, the other mags have the spring loaded conical clutch. The one on the left had the center broken out of the cone, but otherwise they are both the same. The sheet metal cone dates from the EW (350 or 600) era. By the time of the mid-thirties Aero models the cone was a machined iron casting. If the tooth count and offset is right, there is no reason why you can not use them without the clutch mechanism assembled. Pity though, as when you need one these clutches can be hard to come by.

You bike should have the eight spline camshaft; the six spline came right at the end of prewar OHV production I believe.  I have no idea why they changed. Of course, since then there is no telling what type of camshaft may have been installed into the engine. So you do have to check. You can see the end of the spline if you simply remove the retaining nut and washer.

-Doug
« Last Edit: 29 May 2010 at 20:11 by Doug »

Offline eddie

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Re: Magneto differences
« Reply #3 on: 29 May 2010 at 20:50 »
Doug,
           I am only guessing, but I assumed it was done to give finer adjustment of the timing. 8 splines in a 44 tooth gear only permits adjustment by 1/2 a tooth - then it repeats. 6 splines give the option of a 1/3 tooth adjustment before it repeats.
                    Regards,
                                Eddie.

Offline Doug

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Re: Magneto differences
« Reply #4 on: 30 May 2010 at 02:09 »
Eddie,

Possibly, but they already had the vernier adjustment on the engine pinion with its three equidistant keyways on a 22 tooth count gear. I said I had no idea as to why they changed the splines but that is not entirely true. I have no definite idea. I have a theory they changed the spline to suit an experimental (possibly light aviation) engine(s) they were developing during the mid-thirties under contract, and took the opportunity to freshen up the motorcycle tooling at the same time (while charging the expense to someone else!) Speculation on my part and I can not prove it other than there is a drawing that survived for a rotary valve engine bevel gear with the six-spline drive. But which came first, the spline or the experimental engine?

-Doug

Offline Alan Cun

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Re: Magneto differences
« Reply #5 on: 30 May 2010 at 03:02 »
Alex, It should also be noted that the 2 mags shown will have a R right rotation points and pickup ring. You will need L left rotation points and pickup for OHV and S6 T 6 motors. A quick removal of the points cover will show R or L cast into the points body.

regards Alan

Offline alexd912

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Re: Magneto differences
« Reply #6 on: 30 May 2010 at 07:31 »
Hi there,
Thank you all for your quick responses and Im sure by now you have guessed im a total newbie, but trying to learn all the time.

So a couple of questions:
Can I use the recon mag as pictured on on my bike?
If so what do I need to do to get it to work on my bike? I have attached a picture of the mag on my bike.
What is the points cover with the screw on the top used for as seen on the picture.

I have 2 spare old mags with the clutch and one with the dynamo ring as seen on the recon mag. I also have a pancake dynamo and regulator.

I'm willing to make a swap of some of these parts and cash if anyone has a mag-dynamo or spares for a g31.

Best regards

Alex





« Last Edit: 31 May 2010 at 10:27 by Dave »
Best regards
Alex
1930 Douglas G31

 

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