resistance - should there be some

[lawnmowerman]

Hi Bill

I never actually saw my new armature as I asked my Manx Norton restorer friend to rebuild the mag for me and he sent off the armature to a guy he has used for years. He mentioned that when he got the armature back it had the two capacitors and the armature had been sealed with resin. He also said that the capacitors had been replaced with a modern type - I can vaguely remember back in my apprenticeship in the sixties that capacitors were paper and foil construction and there are much better materials available now and the components are a lot smaller and more reliable.

It certainly seems that rewinders earn their money having looked at a few posts previously which had links to the process - the wire used in the HT winding are about the thickness of a human hair

Electronic ignition does seem a good alternative but there is something strangely appealing about a device (mag) where you just turn a spindle and sparks come out of two wires with no complicated circuitry involved. When they are working well there is an certain attractiveness to the simplicity of the design and not a lot can suddenly go wrong as they seem to die gradually with plenty of warnings and can normally get you home.
 
The downside of electronic ignition is that it is reliant on the battery but your idea of a separate battery using a split charge sytem for the ignition should solve that - it is probably similar to that used on caravans to prevent flattening the car battery while using the van electrics.

If you go down that route it would be interesting to see the results.

Jim

[chaterlea25]

Hii Bill,
4.3k ohm is absolutely fine no worries there, Original windings were about 4k, with modern insulating materials some winders get some more turns in
I cant make sense of some of the numbers on the caps fitted to your mag??

The problem with a lot of modern  caps is that they arn't man enough to absorb the high current charge
I have had to repace several from well reputed rewinders
The original foil and mica caps were able to withstand the pulses much better,
Sean Hawker has hand made capacitors like the originals,  Not cheap though
Independant Ignition supplies capacitors seem to be ok, Havn't seen one fail yet
There have been a lot of dodgy sliprings about in recent years,
pitting and tracking on the insulated part of the ring, use a megger tester from the brass segment to the opposite side
What happens when the slipring tracks is that the mag is trying to fir both plugs at the same time

HTH
John O R

[bsa-bill]

Hi John.
I'll see if I can get a pick of the capacitors, tried this morning but my camera died on me, dodgy batteries (Poundstretcher), they show 1.69 volts but last about three. minutes and still show 1.69 volts - what is it about me and electrics?

Pazon arrived today with magneto replacement body, I have had a study, seems straight forward, I'm short of a fuse though and a decent switch, tried the magneto replacement body on the bike, leaves a very useful looking hole down the rear of the engine, thinking I might resite my filter at some time.

I'll take some photo's as I install it,might be useful to someone in the future

interesting remarks you make re the slip ring, I know an electrician who used to service the estate I worked on, I'll get it tested with him at some point

[Stu55Flash]

Interesting thread Bill.

I think your erratic meter readings are caused by the capacitor. To show this properly you need an old fashioned moving coil meter. The needle will sweep as the internal meter battery charges it. Digital meters just show different readings and are not effective at this.  I had my armature rewound after considering the various options. Its between the capacitor dying of old age and the thin HT winding going green and shorting through after several years. One thing you could have tried is wiring an old style car points capacitor across externally to the centre kill connection at the mag and earth. This will help a dying mag for a while. But the only reliable solution is to rewind or go electronic.

Stu

[bsa-bill]

Hi Stu
From advice I've had here it seems the Mag checks out good apart from the maybe  the capacitors or the slip ring,  I have two maggies both show the same results (both refurbished at the same place?)
I do suspect the capacitors but have no way (or knowledge) of testing them with the digital meter I have two AVO meters my dad bought  long time ago, the small one (just a little bigger than a modern one) is very difficult to move the (knob) and the other one is about the size of a shoe box,  need to find time to look at them.
I'm half way through installing the Pazon, I got a call to help out with seed sowing yesterday so a day lost but helps pay for the Pazon

Will report back when I get it in

[bsa-bill]

Well Pazon fitted (pictures taken of the procedure, will post when time allows)
I fitted a pair of not to clean N4's that had been used and failed to start it in the past just to eliminate any advantage new plugs would give, tried them out of the cylinder first, nice fat spark on both ( at the same time ).
With a little trepidation tickled, choke on, eased till it wheezed, a nice determined swing - BAAROOM.
ran it for a minute adjusted the pilot ( 2.5 turns for best running, probably could go back to 25 pilot but hey 1 turn from normal - good enough)

stopped it a couple of times and restarted, first kick each time but need to try the same after a run

So far so ..............................

[muskrat]

 Great news Bill, I know you will love it, even with the down side of having to have a good battery. I got it on all three Beezas.
After your run and it's nice and hot re-do the pilot adjust.
Cheers

[olev]

Hi,
I've no experience with these antiques but below is a 'Tech Tip' copied from the latest HMCCQ club magazine.

< It ran last time out? now there is no spark from the magneto?
Don't despair - yet! Try a Dave Dettmar 'tech tip'.
Remove the contact breaker assembly from the front of the magneto.
(Take out the centre bolt and the assembly, after a wriggle to loosen it, should come out)
Clean the carbon brush behind the assembly & brush track inside the magneto.
The track especially can accumulate a film of oil that with age (& when cold) may thicken and act as an insulator to block the low tension current flow.
Re-fit the assembly, it goes back with a key to locate it in position.
Then try it again - maybe this time  ................? >

Seems to make sense. I don't think the centre bolt should be used as the earth path.
Aren't the bearings and the shaft supposed to be insulated from the frame with a fibre thingy?
and any resistance in the low voltage side will likely have a bigger impact on the high voltage.
cheers

[wilko]

Modern replacement points don't even have the brush?

[Triton Thrasher]

I don't think the centre bolt should be used as the earth path.

Nor did Lucas.  The centre bolt is the live path.

[Triton Thrasher]

Modern replacement points don't even have the brush?

Nor did some original brass plates.

My magnetos have all had an earth brush at the drive end.