Mag V Alternator

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Mag V Alternator

Postby Mollbhan » Mon Oct 07, 2019 10:03 pm

When I was a teen I lusted after a 650 Matchless, the speedo read to 120 mph so (they can do 120 mph you know) however had to settle for a 250 G2 before being seduced away by a Suzuki Stingray 5, a revelation after the G2. Fifty odd years on I have my 1961 G12 with magneto and dynamo and absolutely adore it, not even disappointed to find it wouldn't do 120, in fact never had it more than half that, the question at last is was a new buyer given the choice of either an alternator and coil ignition bike or a magneto and dynamo version, it seems a bit strange to have both versions on sale at the same time?

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Re: Mag V Alternator

Postby SPRIDDLER » Tue Oct 08, 2019 7:15 am

Yes.

See changes for 1959 and 1962 detailed here:

http://www.jampot.com/article_read.asp?id=20
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Re: Mag V Alternator

Postby Mollbhan » Fri Oct 11, 2019 8:27 pm

Thanks Spriddler, makes interesting reading, I suppose when the factory changed to alternator there would have been a stock of mags and dynamos to use up hence the couple of years changeover period.

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Re: Mag V Alternator

Postby SPRIDDLER » Fri Oct 11, 2019 10:15 pm

Maybe not a stock but perhaps AMC had a contract to fulfil with Lucas. Certainly an alternator is a more efficient and reliable generating instrument than a dynamo (Alternating current, higher output, only one moving part, simpler to make etc.). However, I understand that the change to coil ignition was because it was a far less costly ignition system than a magneto in spite of needing the pressed steel chaincase to be changed for a cast alloy one, but even with an alternator it did still depend upon having a good battery, wiring and charging system to keep the sparks coming.
I've never had an alternator equipped bike. I'm a magneto devotee since they are generally exceptionally reliable and I can still ride with a failed dynamo, duff battery, no lights or defective wiring. For me there's something mystical, akin to perpetual motion, about a mag.
I'm pretty sure I've seen AMC bikes with an alternator and magneto ignition......... :?
Cars also ran with DC generating dynamos and coil ignition right up to the 60's, mainly because prior to the advent of heavy duty silicone diodes the rectification of an alternator's AC output to DC was achieved mechanically.
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Re: Mag V Alternator

Postby Groily » Sat Oct 12, 2019 9:13 am

Back in the Dark Ages I always used to envy folk with things like Ton Ten Triumphs equipped with mag AND alternator, as they always seemed to Live in the Light. Compared to my dynamo bikes back in the dim and distant - emphasis on 'dim'.
And even today, even with the excellent regulators available for dynamos, I'd still say that my alternator machines are a safer bet on dark wet days. (Norton managed perfectly well with tin chaincases Sprid.)

I reckon mag & alternator is the best combination frankly, with a combined regulator/rectifier unit such as the Al Osborne A Reg, or a Podtronics or Boyer type.
Zeners are a bit old hat nowadays really, and not much cheaper to replace than swapping for an A Reg. Using the complicated AC/DC switch to cut coils in and out on a (three wire) stator according to load is positively antediluvian, with more potential points of failure than you can shake a stick at.

Probably a lot of truth in the 'contract with Lucas' side of things, which meant AMC ran 'some and some' for a good while. But in the end, cost and perceived reliability advantages killed off mags and dynamos, although like you Sprid I find mags more reliable myself. And have them on a couple of machines that 'ought' to have coil ignition.

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Re: Mag V Alternator

Postby MikeM. » Thu Oct 17, 2019 7:37 pm

Back in the 1970s when I had my first Matchless G12 I used to do evening and night road trials, the G12 was fitted with coil ignition and an alternator and the lights used to fade after an hour or so riding in the dark at around 25 mph, i therefore fitted a mag in place of the coil ignition thereby insuring I didn't run out of sparks and the battery kept relatively charged at low engine speeds.

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Re: Mag V Alternator

Postby MalcW » Fri Oct 18, 2019 8:12 am

Mollbhan wrote:When I was a teen I lusted after a 650 Matchless, the speedo read to 120 mph so (they can do 120 mph you know) however had to settle for a 250 G2 before being seduced away by a Suzuki Stingray 5, a revelation after the G2. Fifty odd years on I have my 1961 G12 with magneto and dynamo and absolutely adore it, not even disappointed to find it wouldn't do 120, in fact never had it more than half that, the question at last is was a new buyer given the choice of either an alternator and coil ignition bike or a magneto and dynamo version, it seems a bit strange to have both versions on sale at the same time?


I seem to recall reading somewhere that when they went to change over to alternators, the feedback to the company from a significant number of people was that they wanted to retain the magneto setup. Hence two setups being available, for a while at least.

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Re: Mag V Alternator

Postby Groily » Fri Oct 18, 2019 1:48 pm

Maybe AMC had a load of dynamo timing side crankcases for twins lying around too Malc, so instead of giving us the Mag Alternator option like Triumph and Norton, you got mag & dynamo or battery/coil and alternator. And then no more dynamo and magneto option when the castings were all used up? Did AJS/M ever offer mag and alternator together from the factory - brain fade maybe, but can't think they did?

I imagine mags were more £sd than dizzies and alternators were maybe? cheaper than dynamos, which if so will have driven some of it I'm sure.

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Re: Mag V Alternator

Postby dave16mct » Fri Oct 18, 2019 2:48 pm

? Did AJS/M ever offer mag and alternator together from the factory - brain fade maybe, but can't think they did?

Yes 650CSR from about '63 or '64 had mag and alternator.
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Re: Mag V Alternator

Postby Groily » Fri Oct 18, 2019 3:47 pm

Thanks Dave.

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