BSA B33 / B31 swingarm models

Any experts here? I was told the primary cases from these models will bolt up to Goldstar cases. I believe this would allow me to use an alternator. True?

seattle##gs said:

Any experts here? I was told the primary cases from these models will bolt up to Goldstar cases. I believe this would allow me to use an alternator. True?

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Yes they will bolt to gold star crankcases
But I'm guessing you'd need to use a B series crank as the gold star crankshaft won't take an alternator rotor
What are you trying to achieve?

And obviously the b31-b33 chain cases would have to be the alternator type

I bought my Goldstar right out of high school, 1972. At the time I knew very little about British bikes. I had ignition and electrical problems for decades, the first big leap forward was getting a Boyer crank triggered ignition but the awful magdyno and it's even worse mounting on the motor has kept it from being reliable. Two years ago I put in a new crank and rod assembly for a DBD and I would like to use a Joe Hunt magneto. JH has single fire mags but seem to be reluctant to sell one. I was talking to Jaye Strait today and he said it would be easy to install an alternator if I had the correct cases. This would solve a lot of problems right away if it's possible. I can still use the crank triggered ignition instead of using a total loss system.

seattle##gs said:

I bought my Goldstar right out of high school, 1972. At the time I knew very little about British bikes. I had ignition and electrical problems for decades, the first big leap forward was getting a Boyer crank triggered ignition but the awful magdyno and it's even worse mounting on the motor has kept it from being reliable. Two years ago I put in a new crank and rod assembly for a DBD and I would like to use a Joe Hunt magneto. JH has single fire mags but seem to be reluctant to sell one. I was talking to Jaye Strait today and he said it would be easy to install an alternator if I had the correct cases. This would solve a lot of problems right away if it's possible. I can still use the crank triggered ignition instead of using a total loss system.

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B series alternator chaincases are not that common in the UK and rarely come up for sale
You'd have to totally revise your crank mounted Boyer if you fit a Lucas rotor IE permanent magnet on the end of the crank
I'm assuming you'd fit a b33 alternator type crankshaft so you can mount an alternator
I think getting the magdyno rebuilt by an expert would be my choice tbh
Or maybe fit an Alton alternator to the dead magneto and keep your crank triggered Boyer

If you want to fit a mag then look at the BTH website. My mate has one of these on his Phil Pearson engined 600 Norstar. It always starts first kick & idles like a clock. I should ad that it goes like stink too. I think they are a similar price to a JH. They are self generating as the old style mags, but a modern electronic version.

I fit an alton alternator to the magdyno. The big problem there was the mag is harder to turn than the original Lucas 6v unit. It caused the fiber gear and the large spring to slide past each other but I didn't realize what was happening for a couple of years. It started out bit by biit and slowly got worse. So it would only partially charge and the battery was always going dead. On top of that the entire madyno would wag back and forth especially when it was started. Eventually this wagging would pull the gear off it's taper. The whole thing is a mess of bad engineering. I've since taken the cases and milled the mag platform flat and milled the timing chest flat where the mag goes through. I want to bolt something to the back of the timing chest so it will be secure and, finally, square to the gear train. If I could run an alternator off the crank then my charging problems would be over. Perhaps I could buy a couple of Shorai batteries and run a dead loss system. The magdyno generator turns faster than engine speed so it can't be a direct drive.

If your crank-triggered Boyer is the Micro Power racing set, I gave up on ever getting it to work right and I am not alone in that.

If that's the one that has the negative ground then that's what I have. It worked very well just give it a reliable 12V.
I've heard of people having problems with it. Is there a better form of ignition for these bikes?

seattle##gs said:

If that's the one that has the negative ground then that's what I have. It worked very well just give it a reliable 12V.
I've heard of people having problems with it. Is there a better form of ignition for these bikes?

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IMHO the best form of ign for an old Brit single is a good mag. Or a modern version like a BTH as mentioned above.

Huge spark and dead reliable. Whats not to like?

They only get a bad rep cos folk are using 60-70 year old devices that are thoroughly clapped out and have had decades of botchery !!

OK. I'll look for a BTH.