Magneto gear question

[ADP91]

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

[a10 gf]

Something like this  :

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.

[muskrat]

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

[ralph]

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?

[bsa-bill]

(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

[duTch]

 
 In addition to all the above, if you have a Haynes manual I'm sorry 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

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

 
 
 

[terryg]

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.

[groily]

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.

[muskrat]

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

[kiwipom]

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

[trevinoz]

Looks like Triumph. How many teeth?