Removal of ML magneto

[Andy24]

Hi,
So there was me thinking buying a 1924 BSA roundtank would be a great idea, how hard can it be to get it going again. I've watched all the usual bike programmes where they clean the plug and points and tickle the carb and off they go. Hmmm some chance.
So being very new to the vintage world I've started to try to recommission my new(very old) round tank. First thing was no spark. New spark plug, still no spark. I've cleaned the points and checked the gap and they seem fine. They rotate as they should and open and close. The cam ring turns when the Advance/retard lever is used as it should. I have continuity through the HT lead. So I decided to get the Magneto off to either try and open it up to check inside, not that I'm entirely sure what I should be looking at, or to take it somewhere to get it refurbished. I've managed to detached the Ad/retard cable and HT lead. I've got the front case off and the points out. I've removed the casing on the offside of the motor and am now stuck as to how to remove the cog which seems to be on the shaft through the magneto. There's a nut but I can't see how you can hold the cog/magnerto shaft whilst trying to undo the nut. From what I've discovered the cog is held on a tapered shaft which I understand I'll need a puller to remove the cog but can't work out how to remove the nut or if I even need to. Apologies for the long winded question but figured it best I explained where I'm at and what I've managed so far.
Any advice would be great.
Thanks Andy

[limeyrob]

Before you go any further I would put the mag back together, you can do a lot of damage. You'll needed a puller to get that ger off once the nut is undone but do that and you loose the timing so I would be putting the mag back together and doing some more cleaning of the points and brushes.
You got the mag armature on one bearing and there are some easily damaged parts so stop now until you have read the manual for the mag. I've seen too many with broken slip rings due to being dismantled in the wrong order.

[Andy24]

Hi,
Thanks for the advice. Any idea where I might find this manual you both mention. I'm new to the club and new to the world of vintage and this age of bikes. As for putting the front case etc back on the magneto I'm still unsure how that helps me in undoing the nut that appears to hold the cog in place. I understand the need for a puller to remove the cog/gear correctly but as soon as I try turning the nut the spindle or axle for a better term that runs through the magneto just turns and will turn the points etc if back in place. Also the brushes you mention, I've yet to get that far into the magneto. The points are definitely clean and the picture on the right is as far as I've got dismantling the mag from the points side as two of the screws are completely siezed hence why I need the mag off to take it to an engineer to get them removed with no damage.
Thanks again Andy

[Andy24]

So forgive my stupidity, as I say I'm am very new to this age of bike and am learning as I go. I've done some more googling and it appears I've seen the brushes you mention. I just didn't realise the brushes looked like that, I was looking for an actual "brush" I did say I'm new to this 🤣
I've seen two "brushes" one attached to the HT lead and one somewhere else which I can't remember off the top of my head. I did give both of those a clean, as for the timing sadly I think I've already messed that up by trying to undo the gear and turned it to a different position it was in. That at present is the least of my problems.
Andy

[idie]

You really should try to keep the armature back in the magneto body as it acts as a keeper for the magnets in the body.

[Steve.S]

The National Motorcycle museum have Instruction manuals for this Magneto.
If you search You Tube for "Lister A 1924 vintage engine ML magneto strip down", you will find a helpful video.
To remove the drive pinion (cog), you need to refit the idler pinion, then you can jam something between the teeth to lock the pinion. Ideally, a very small pinion can be dropped between the teeth (if you can find one). I use one taken from an old Black and Decker jig saw. But be careful if using a screwdriver as you may chip a tooth. Use a big one. You could also make a jam from round bar with a diamond shaped end, to fit snugly between the teeth.
If you do decide to remove the armature, (the spindle or axle you refer to) be sure to remove the earth brush first, and as suggested use keepers.
If you search the Brightsparks website, you will see how to check the secondary windings using a multimeter.
If you have removed the armature you can also see if the armature is producing a spark by connecting a battery. With the points base plate removed, wrap a piece of copper wire around the slip ring (the bobbin the HT brush runs on), and then bend it so it is about 3/16" away from the body of the armature, connect one side of a 1.5V battery to the body and jab the other end on the points centre screw. It should produce a spark each time you jab it.
Let us know how you get on.

[Andy24]

Thanks so much for the advice, as I say I'm very new to this age of machine and already feel like I'm fumbling around in the dark. I'm already learning things like what the actual armature is that I keep reading about. Lots more googling for me before I attempt any more. The armature is still in the magneto body, if I'm correct I don't think I can get that out without having first removed the cog from the other end of the armature. Again thanks so much for the constructive advice, much better than the RTFM response I first received which now seems to have been deleted by whomever posted it.
I will do so more research and let you know how I get on.
Thanks

[limeyrob]

Brightspark magnetos have up loaded some of the manuals, I have put the links below.
A magneto is a piece of precision equipment and you should think of it like an antique clock, not a bit of old motorcycle.  Take it apart the wrong way and you can do a lot of damage.

https://library.brightsparkmagnetos.com/library/ML%20Magnetos/index.htm 

A magneto will reliably produce decent correctly timed sparks for over 100 years of use, there's no other ignition technology that comes close. They need periodic oiling and cleaning, but not much more. Most of the damage I have seen is due to them being dismantled wrongly or overheated.

[Andy24]

Thanks for the link, I've found out it's an ML MCK1 apparently from what I can see on the side of it. I'll take a look at the YouTube previously mentioned and the link you've provided, fortunately I'm up at the national motorcycle museum next week so hopefully I can get a manual then.
Thanks again.

[limeyrob]

I took a look at the pictures and it looks like it has a safety screw on the underside. This means the armature MUST stay in until that is removed. There will be an earth brush too but I'm not familiar with ML mags.

[Andy24]

Thanks for all the advice. I'll try and get the manual from the museum next week and see if I can speak to any of the restorers there.

[Steve.S]

You are quite correct in saying that the cog has to be removed before you can withdraw the armature. Use a puller and do not try to lever it off or the alloy crankcase extension will break off. Likewise if you use a screwdriver between the teeth and the extension to trap the pinion (cog!) whilst undoing the nut.
I must say that dealing with the intricacies of a magneto as your first foray into vintage motorcycles is interesting, but you have to start somewhere, and you will learn a great deal. As mentioned, just try not to break anything.
Once the armature is out, it's easy to check the secondary resistance (the most likely problem, together with a faulty condenser.) Just connect a multimeter on Resistance, to the brass in the slip ring and the end of the armature shaft. It should read about 4,000 to 7,000 ohms. It not, it is almost certainly Fubar, and I would recommend sending it to Armoto for attention.   

[Andy24]

Thanks again for all the advice, and yes tackling the magneto of a 102 year old bike wasn't exactly part of my grand plan when I bought her but hey you live and learn and I'm definitely learning. I took a look at the you tube video you recommended and it helped alot in recognising the parts and putting correct names to them. I do need to get my eyes on a manual though, the video suggested the earth brush was a screw on the top case opposite side to the HT lead but mine doesn't have one, the only screw on the top seems to prevent the cam ring turning further than it should in either direction. I'll be back in the garage in the morning so will investigate more.
Again thanks for all your help so far. I'm sure this won't be my last post pleading for help  😬
After all I've got to put it all back together at some point and get the timing right.....

[Andy24]

One quick question, is it possible to check the secondary resistance without removing the armature, possibly by feeding a copper wire with insulation around the wire so it doesnt connect with the mag body through the HT lead opening down on to the slip ring and then connect the multi meter, one to that wire and the other to the armature shaft? I'm just thinking if that test proves the secondary  resistance is fine then I might not need to remove the cog/ armature and prevent any damage. Which I'm guessing, probably wrongly, would suggest the slip ring needs a good clean and another good clean of any brushes and points. Ever the optimist.

[limeyrob]

I think the short answer is yes. The problem with removing the armature is that there almost certainly is a steel safety screw, this is about 3/4" long and sits in the middle of the (fragile) slip ring. It stops the armature being removed and should anyone try it hits the slip ring and breaks it.  It looks like the screw on the ML is removed from underneath so you can't get to it with the mag on the engine.  Its job is to earth a HT spark if there's no HT connection to stop it  sparking inside the windings.
I would reassemble the mag end cover with the existing shims and check it spins freely with no end float.  Strip and clean all the parts of the points and clean the HT brush and spring.  You can put a cloth in the HT hole and turn the mag over to clean it.  Do the same for the earth brush and slip ring (where ever they are on your mag).
There's a chance that after this is will spark. Mags are very sensitive to dirty points and corrosion where the points bolt to the holder.
If you do a search there are some examples of simple electrical tests, I'm sure one is slip ring to points holder.
Make sure you have the rotation correct, then you can spin it up with a cordless drill and a short bit of rubber hose on the nut.