Thread: Magnetos....... anyone have the knowledge?

A magneto is two things. A spark maker and a spark distributor. If you have one that is making good spark then the problem is in the other part.

Jack Ussher of Grafton is one of the few good old magneto repairers left above ground. He is in the book.

Thanks Brian.

I'm aware the prob with this thing is probably the distributor or condenser, but it does have an unusual (stock) impulse mechanism on it that doesn't connect to the mag body.

I don't want to pull that part apart if unnecessary, just hoping to find advice as to what is normal with the impulse mechanism on this particular mag. (and why it has a massive spark if spun in reverse)

cheers, DL

A impulse maggy should in its normal direction of drive if turned slowly by hand give a good spark and snap over type action when it does fire.
This snap over type action only occurs at cranking speeds in its normal direction of rotation.
The main wearing parts of a maggy are the the brushes and points.
brushes are carbon and are easily made.
Maggies can be affected by water and the old trick was to place them in a slow oven to dry them out.
The type of maggy you have as a last resort can be converted to kettering ignition by adding the correct type of coil and use the original maggy points to trigger the coil.
The type of magneto you have with impulse when its working is a better system to Kettering and even some electronic ignition systems.
Other things to look for is wear in the bearing or bushes which could be shorting out the internals of the maggy and if turned backwards reduces the wear enough to allow it to work and the impulse is obivous if it does work as the snap over is strong and positive.

Brushes are easy to check and are the wearing component.
Usually located 180 degrees apart at one end of the maggy.
They can wear too short(even if they look good) and not contact the slip ring
which must be clean
Points on a maggy tend to be good quality and usually can be filed clean and the points face do not seem to wear like kettering ignition.
Points rubbing block wear will cause problems and the points gap on most models tends to be small ......like about 10 thou.
Ron

Thanks Ron.

Its a simple ignition magneto, doesn't have brushes. Am getting another distributor and condenser. Points are new and correctly gapped, leads are good.

On most of these things the gear drive interacts with an impulse mechanism on the housing via a spring, however on this one the gear interacts with a mechanism on the end of the shaft via spring, only has about 15* of movement and appears to be more for advance or retard.

cheers, DL

magnetos all tend to be slightly different in design.
I do know the impulse drives tend to be very reliable.
They will stop operating as impluse between 90 to 200 rpm.
Some maggys have a brush for the HT too.
They are fitted with condensors too which should be tested.
the fact yours is throwing a spark in reverse indicates a bearing , brush or drive problem.
I have two two cylinder magnetos looking for a good home, impulse type originally from a 10/12 Clae marine motor.
A work mate when I was a appprentice gave me a 1920s Cassels magneto adjustment and repair and It still is a great reference tool for these spark throwers.
Got any pics ?

Yep, HT graphite post in dist is worn as is one of the posts that the geared rotor system runs on. Have tweaked all this as much as I dare which has improved things.

My uncle has a collection of magnetos from his old tractor 'museum' and has found a dist that will fit, along with another condenser which I will try.

Re: pics, PM sent.

cheers, DL

OK........ for those who were interested:

My Uncle sent me a very similar Wico magneto that had an actual impulse mechanism attached.

The spring loaded attachment on the end of the shaft on mine is an advance / retard device, not impulse. Was apparent that I was actually spinning it the right way when getting big spark, which was somewhat intermittent at the plugs at slow speed.

Intermittent spark caused by worn bearings in the body I had affecting points, so was swapped. A fair bit of work getting it all sorted, but all is good.

The Howard fires on the first compression stroke when carby is primed without using decompression, quite impressive really for a 810cc twin.

Ploughed a couple of 50M long beds on the 13th (3years to the day after my dad died.........it was his Howard, and also on the same date as my grandfather's birthday (Ted Hall) who taught me everything about mechanicals.

cheers, DL