Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board SR1 Magneto on a B33?

I recently purchased a Lucas SR1 mag with hopes of using it on my B33. I have read many posts that attest to the feasibility of this conversion, however, they are short on details. What I need to know is, in this configuration, how is the mag driven and what parts do I need? I also know that I'll need a spacer plate to raise the mag into position. The bike will not have lights.
Tom

I think the standard drive gear will fit.

One thing to be aware of is that the SR1 is fixed advance, which could be a challenge.

The drive gear with a built-in advance mechanism as used with the KF2 might happen to fit and have the appropriate advance characteristics.

That doesn't sound like a good solution to me. The K2F drive gear is too big to fit in a B33 case and the tooth count is wrong.

The great tragedy of Britbike - the slaying of a beautiful hypothesis by an ugly fact.

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It should be simple, right? The SR1 that I have does not have a drive. It was probably from an AMC single, which use, I think, a chain drive. I thought that perhaps the drive mechanism from a MO1L could be used. I bought a drive plate/pinion, but the center hole is too big.
Thanks for the insight thus far!
Tom

Could you show us the end of the shaft. Are you saying a pinion for the MO1 mag will not work on your mag?

Gordo

The end of the shaft is identical to the thrashed MO1L that I have. The pinion, a hopeful Ebay purchase, does not fit either mag. The hole is oversized. I will snap some photos later today.
Tom

Hi
The original pinion should fit any standard Lucas / BTH magneto
The SR1 is not a good choice as when the ignition timing is set the bike will be very hard to start and kick back nastily
retarding the ignition so it will start will ruin the performance and likely cause overheating
My advice would be to buy a reconditioned MO1L or a modern substitute, that way you can retain the dynamo for lighting and have proper ignition timing control

John

Thanks John. This is what happens when I try to simplify. For what it is worth, I am not going to run lights, the bike will be a in trials trim.

This is the shaft on the SR1.

The shaft roughly measures 3/8at the threaded end and 1/2 at the end of the taper. It is 1/8 longer than the shaft on the mag behind it. Below is a pic of the pinion which has a bore size of 9/16.

The item you are showing looks like the plate with peg that drives the Dynamo fiber gear on the MO1L mag. It would be hidden behind the cover plate on the MO1 mag. The pinion that fits onto the mag shaft is much smaller and has teeth to engage the idler gear in the timing chest. It matches the taper on the shaft and does not need a key.

Your new mag would not need that pegged plate you are showing as it has no dynamo.

Gordo

It appears that I have been 'reading' the MO1L diagram backward and confusing the drive for the dynamo with the drive for the mag! I'm off to search for an ATD that might suit...if such a thing exists...

The MO1 diagrams I have do not show the pinion that goes onto the mag shaft. All the parts shown behind the end cover are for driving the dynamo that sits on top. The mag pinion goes on the outside of the end cover. The diagram does show the nut that secures the pinion.

Both the mag and the dynamo are driven from the same side.

Gordo

Hi pigpen,
If you removed the MO1L from the bike you will have the correct pinion ??
If not the part number is 65-1879

John