The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: ADP91 on 29.05. 2016 20:51

Title: Magneto gear question
Post by: ADP91 on 29.05. 2016 20:51
Hello all,

I'm building up an a10 engine and I am not sure of the difference between automatic and manual advance gears for the Lucas magneto.

Could someone enlighten me?

Cheers, A
Title: Re: Magneto gear question
Post by: a10gf on 29.05. 2016 21:12
Something like this  *smile* :

The 'normal' (fixed) gear drives the mag shaft directly. Timing set by rotating camring in the magneto, operated with wire to handlebar lever. = manual timing.

The auto gear drives the mag using centrifugal weights to change timing according to rpm, changing relationship gear outer teeth vs mag shaft. Mag has fixed camring. = auto timing.
Title: Re: Magneto gear question
Post by: muskrat on 29.05. 2016 21:25
G'day ADP.
Pics of the different pinions. (the manual one should be fiber as well)
At the points end are different for the manual advance cable.
Cheers
Title: Re: Magneto gear question
Post by: ralph on 30.05. 2016 08:47
G'day ADP.
Pics of the different pinions. (the manual one should be fiber as well)

Indeed it should. there are ali pinions available, but I wouldn't use one. Ive seen a seized mag result in stripped teeth on a tufnol pinion - and that is what you want. fit an ali one and something more drastic my break apart in the timing chest. Ive had a fibre (tufnol) gear on running for nearly 28 years and showing no sign of wear. I wonder sometimes if the tufnol soaks a little oil into the surface like oilite bushes?
Title: Re: Magneto gear question
Post by: bsa-bill on 30.05. 2016 08:59
Quote
(the manual one should be fiber as well)

all well and good, are they available though,  fifty years on you sometimes have to take what you can get
Title: Re: Magneto gear question
Post by: duTch on 30.05. 2016 09:38
 
 In addition to all the above, if you have a Haynes manual I'm sorry *conf* but on page 43 of mine is a vague showing of this being installed.

 otherwise this link might shaow what the ATD actually looks like;
 https://images.duckduckgo.com/iu/?u=http%3A%2F%2Fbrightsparkmagnetos.com%2Fimages%2FLucas%2520ATD.jpg&f=1 (https://images.duckduckgo.com/iu/?u=http%3A%2F%2Fbrightsparkmagnetos.com%2Fimages%2FLucas%2520ATD.jpg&f=1)

 well that's a coincidence- just pulled a random image from the internets *smile*

 
 
 
Title: Re: Magneto gear question
Post by: terryg on 30.05. 2016 12:21
Priory Magnetos (beezermacc) had good stock when I needed a replacement fibre gear for a manual mag, and sensibly priced including rivets to fit it.
Title: Re: Magneto gear question
Post by: groily on 30.05. 2016 16:49
Yup, they were fibre, but I ran on alloy for ages without problems to be honest, with a fixed gear and also with one modded to take an atd as an experiment, although I'm back on fibre + atd just at the mo.
Yes, if the mag loses its insulation and seizes up solid bad things can happen - but it's more common for the gear to shed teeth owing to wear and tear, which is a pain. I've lost 2 fibre ones on Beesas over the years, neither through seizures.
AMC twins use steel pinions, sprocket and chain drives are obviously steel (Nortons, Oilfield twins, many magdynos, etc). So are most if not all 4 cyl drive trains. So I wouldn't worry about using a steel or alloy gear myself -there's a lot going for them.
Title: Re: Magneto gear question
Post by: muskrat on 30.05. 2016 20:57
I use the alloy on both mine but also electronic ignition.

G'DAY RALPH. Please introduce yourself here http://www.a7a10.net/forum/index.php?board=13.0 with a new topic.
Cheers
Title: Re: Magneto gear question
Post by: kiwipom on 31.05. 2016 07:19
hi guys, anyone know what this one is off, I got it with spare parts when I got my A10 some years ago, as far as I know it is no use to me,cheers
Title: Re: Magneto gear question
Post by: trevinoz on 31.05. 2016 22:21
Looks like Triumph. How many teeth?