Removal of ML magneto

[Andy24]

Thanks gents for all the advice, I've definitely learnt lots from this post. I've identified the HT brush, the only other brush I have found is on the reverse of the brass mount of the points, I'm assuming that earth's against the points cover which in turn earth's to the main mag body. Other than those two I haven't seen any other brushes or found any other screws that have anything that resembles a brush attached to them. I think I'm going to try the secondary resistance test followed by a good clean of all parts before putting the points and cover back on, then I'll see where I'm at. Then just need to get the timing sorted as I replace the cogs and cover on the offside of the engine. Fingers crossed 🤞

[Steve.S]

I think I may have confused you regarding my 2 separate suggestions of 1. Checking the resistance and 2. Testing for a spark using a battery.
When checking the resistance, there is no need to wrap a piece of wire around the slip ring, just touch one lead of the ohmeter to the brass on the slip ring and the other to the end of the armature. I suppose you could place the probe through the pickup hole?
I have not seen a magneto without an earth brush, (but neither have I seen an ML magneto) which would run on the brass at the opposite end of the slip ring. This would be in addition to the brush you have found on the points base plate. However, even if there is a hidden earth brush, and you remove the armature, the worst you will do is break the carbon brush. (Easily replaceable.)
Normally, the resistance would be checked with the armature removed from the body, to eliminate any possible false readings.
You really must bite the bullet and remove the pinion. You may be lucky with giving it all a good clean and repack the bearings, but this is most unlikely, and to do this you will have to remove the armature anyway. As you go through the machine, you will find that you have to use a puller on various things, so you might as well start now.
My understanding regarding spark safety gaps is that they are only used on multi cylinder machines, since if the HT becomes disconnected on a single cylinder machine, the engine will stop and so the magneto will not produce a spark.
On a twin, if one lead becomes disconnected, the engine will continue to run and the spark will have nowhere to go, so it will try to spark inside the windings, hence the safety gap. But what do I know.....

[limeyrob]

I agree the earth brush and safety screws are confusing.  My K2F twin mag has two safety screws but my K1F single (on a Matchless) also has a safety screw and unlike the the K2F where you can see them, its underneath.  There is a screw underneath on the ML which could be the earth or it could be the safety, either way it looks like it can only be removed with the mag on the bench.
The safest thing it to put the end cover back before taking the gear off so the armature can't end up resting on the screw or brush.

[Andy24]

Thanks again, I've been in the garage this morning. Thought I'd try cleaning the slip ring through the HT lead opening. Used a clean cloth soaked in petrol and held it gently in place with a screw driver. Fear not the cloth was doubled over and very minimal pressure was used. It actually seemed to remove a fair amount of what must be carbon build up. It was difficult to see properly but when I'd finished it certainly appeared cleaner. I tried the secondary resistance test, managed to get one probe through to the slip ring, the other held on various positions on the armature spline where the points fit, got absolutely no reading. However as pointed out that isn't definitive with the armature in situ. So I decided to try my luck, cleaned the brush on the end of the HT lead and the one which protrudes from the rear of the what I think is the points base plate, cleaned the contact point of the points case where that brush will or should contact. Greased the bearing ring, reattached the points case and then the points back plate. Attached HT lead, brand new spark plug, re checked the points gap and went for it eith a drill in slow speed attached to the nut on the cog. The armature spins freely and easily, doesn't seem to wobble and the points open and close just no bloody spark still 🤪 told you I was the eternal optimist. I'm going to the motorcycle museum next week to get the correct manual and see if there are any of the restorers around to show pictures to in the hope they can point out stuff.  I really appreciate all the advice you have both given. It's definitely helped me in learning parts names and things not to do and things to try. I'll keep you updated on how I get on. The only other thing I have thought is to try new brushes, not sure if you guys know a good place to get some from. They are on ebay but who knows where they've come from or quality.
Thanks again.

[limeyrob]

Well you've made a lot of progress even if its not fixed yet.  Mags can be very frustrating, I spent hours building up one from all my best parts and had persistent misfiring and poor starting. Out of frustration I put all the left over parts together to make a 2nd mag and its been a gem. I then wasted hours substituting one part for another to work out why one worked and one did not and I never worked it out.

[Steve.S]

Thank you, Rob for putting me right on safety gap screws.
Andy, I would purchase brushes from Brightsparks. I'm sure they're good quality.
I had an armature rewound a year or two ago, by one of the best rewinders in the UK. It worked fine for a while, and then became difficult to start. The spark seemed to come and go on a Spark Gap Tester. It was OK on full advance, but poor on full retard...(you may want to try for a spark on full advance.) Everything looked OK, secondary resistance was good, so I sent the whole mag away to be remagnetised....just in case. No difference. Just like you, I spent weeks of checking, I finally renewed the pickup brush with one of unknown origin, even though the old one looked OK. Well, it made a difference, but not for long and I was forever having to clean it. Then I bought a new brush from Brightsparks, and, fingers crossed, it seems OK now. We shall see.
From what you have said, it does look as though the secondary windings have a break in them.
I wonder if Rob can add to my encouragement to remove the pinion? Otherwise, you're just going around in circles.

[Andy24]

Thanks, from what you guys have said about problems with magnetos it's reassuring that it's not just me. I think I'm going to find something to help hold the pinion safely while I try to loosen the nut then get a puller to remove it, once off the whole mag is going for refurbishment.  I haven't decided where yet, I've seen various places recommended on other forums. There's several screws with heads that have nearly been stripped and two that are gone completely so it wouldn't do it any harm to have a full refurbed looking to the future.
Just to further my knowledge,  if as I say I tried to spin the mag with the drill directly on the nut holding the pinion to the armature but didn't have the advance/retard wire attached and I think it's a tight wire advance, would that make any difference to getting a spark? And I'm right in thinking even if the mag was completely free from the bike so long as I held the spark plug against the engine block I'd still get a spark if all was working fine? I'm just confirming I don't need to put the other three pinions and case all back together and get the engine correctly timed just to achieve a spark?
Andy

[V500]

if the mag is "completely free"  from the bike then the plug won't spark on the engine block no matter how good the mag is.
Place the plug against the mag body if you want to check the spark.

[limeyrob]

They are set to spark best at full advance so you do need the cable to pull the cam if its tight wire advance.

[Andy24]

Okay thanks, again just for my future knowledge. If the mag isn't on the bike and thus the timing of the engine/piston has no bearing on when it sparks for best combustion surely it wouldn't matter if advanced or retarded if I'm just trying to create a spark from the magneto? I bow to you guys far better knowledge.  Am I confusing the whole point of advancing or retarding when the spark occurs?

[V500]

For technical reasons of getting the best spark you need to put the mag at full advance to get the best spark for testing when it's on or off the bike.
All to do with the intricacies of peak flux density etc.

[Andy24]

Okay, that just proves how little I know and how I wish I'd listened more in physics o level all those years ago. 🤣

[Steve.S]

There are 2 separate reasons for advancing the ignition timing on a magneto. The first is that it allows the engine to develop more power which means you go faster. The second is that, as has been said, the magneto produces a bigger spark when advanced, but probably won't make any noticeable difference to power output.
You might want to invest in a Spark Gap tester. Otherwise, forget the spark plug, (it may be faulty) and just securely hold the end of the HT lead about 3/16" to 1/4" from the body of the magneto with it in the fully advanced position. It should produce a spark.
You do not need to put the other 3 pinions back together and time the engine just to produce a spark. The magneto is completely self contained.
Do remember to spin the magneto in the correct direction of rotation, and also that if the magneto spins, say, clockwise viewed from the drive end, it will spin anti clockwise when viewed from the points end.
The face cam will turn in the opposite direction of rotation of the points to advance it.
You may find a copy of "The Vintage Motorcyclists Workshop" by Radco useful.

[Andy24]

Thanks, I'm slowing getting to understand all the wizardy that happens in a magneto. The spark plug I'm relying is brand new and have tried several other brand new ones and no joy so I'm guessing there's something more than that. I'll try the HT lead near to the housing just for the hell of it. I think I just need to put my big boy pants on and get the pinion off then I  can send it off for a full refurb.
Not today though, the sun is out and one of my other rides is screaming at me to take her out. Off to have some fun...

[Andy24]

Trying not relying