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Re: Magneto question

Hi

Have you got a heat resistant spacer between the carb and the head?

If not, then that could perhaps explain the difficulty starting when the engine is hot.

Apologies if you already have one and have discounted this.

Regards

Pat

email (option): meagher_family@hotmail.com

Re: Magneto question

Hello Mike,

Your magneto model should be OK, as it is s M01L 46043A Anti-Clock Direction.
The problem to start when hot can be related to the capacitor in the mag,
The winding of the armature, an air-lock of the carb,(Do you have the tufnol piece?)
The spark plug, the HT cord, the fuel mixture, the ignition timing...

I would spend some time to go over everything else, as all the rest of the list
Is easy and fast, and would leave the magneto as last in the list.

Good luck,
Noam.

email (option): noam10@gmail.com

Re: Magneto question

I think Tony Cooper could recon two mag's for that price.

Re: Magneto question

Ian Wright had one for sale recently

It will be well sorted knowing Ian

Best regards

Job

email (option): Jonnyob1@googlemail.com

Re: Magneto question

Pat & Noam, Unlike the M20, the M21 has a separate aluminium inlet flange 1&3/4" long which I assume as there is no more room on the studs is sufficient to dissipate the heat. The carb is a new monobloc correctly jetted. I have fitted new copper HT lead and low resistance NGK plug cap. I have tried different plugs and the bike has LOADS of compression, I've also checked and double checked the IGN timing. Lovely blue/white spark when cold, less so when hot.

Re: Magneto question

It is the classic symptoms of a failing mag...

I agree with Ians comments..SRMs £300-400 price tag is at the top end of this sort of work...

Pretty much normal for SRM...

You can still get change from £250 for a properly executed mag overhaul...Ian

Re: Magneto question

Magneto condenser. There are a few options, the easiest is from:

http://www.brightsparkmagnetos.com/

Very knowledgeable guys. there's an ongoing discussion between them, and someone on another site, but I'd trust these guys first for a fix that'd at least get you on the road. I rebuild mags myself (although most of the time it's a maintenance issue, with a few condensers required) and it's not a cheap thing. So, an easycap, could get your wheels moving, and give you breathing space if you want to go the whole hog.

I've read a hell of a lot of info on mags (I'm an electrical/mechanical engineer) and it's still weird science to me, with much more to find out. But, one thing I've grown to realise, is that if more people followed maintenance advice from BSA, Triumph, Matchless etc, but mostly LUCAS (it was all tucked away under the hard to find, easy to ignore section, titled MAINTENANCE), there would be a lot fewer people complaining of the difficulty they had starting their bikes, and reliability complaints may not have forced bikes into the back of peoples garages.

email (option): oldjunk@btinternet.com

Re: Magneto question

The Lucas magnetos of the types fitted to 40s/50s bikes are essentially reliable units...very reliable...

Many problems come from attempts to get that reliability from 60-70 year old units of unknown provenance...It's a no brainer really...There will be problems...

I wouldn't imagine that requirement is imposed on the various items of equipment used in most peoples lives...50 year old washing machine?...No...

I still use bikes equipped with standard spec Lucas magnetos (accepting of course armature rewinders don't use a shellac coating any more etc.)...

However, every bike I rebuild gets a freshly rebuilt magneto and bluntly, poor starting and unreliability is not an issue I have to think about....

I don't run a car and use my old bikes to varying degrees as my transport. I don't recall exactly when I last had a serious magneto problem...It was a long while back...

I do recall it was a bearing failure that led to that magnetos demise...

I am having some starting issues with my recently purchased TRW which is equipped with a BTH magneto...For now I live with it but expect the replacement I am having rebuilt to eliminate the problem for some time to come...

Rebuild any mag that you don't know the full history of or that has been on a bike standing in a garage for years and you won't have much touble..That's my experience over a 45 year period anyway...Ian

Re: Magneto question

Hi mike

I note you mentioned a low resistance plug cap - for the sake of longevity - the plug cap should be a non resistive type

Although condenser failure is the most common issue - I had a mag failure which was related to a slip ring - very same symptoms as a failing condenser - hard starting when hot being the most obvious issue

It was brightspark in fact diagnosed it for me

Best regards

Job

email (option): Jonnyob1@googlemail.com

Re: Magneto question

We've been through this before and I have to say I like the 'Brightspark' but there are a couple of things to remember when comparing the 'like for like' cost of a Brightspark versus a mag overhaul...

The Brightspark can solve the problem of accessibility to the condenser BUT...

You have to have the facilities/tools/knowledge to do the initial fit...

If you don't have these you can do as much damage to your magneto as good...

Of course you could take advantage of Brightsparks fitting service but I'm guessing that would cost quite a bit extra...

Also you still have the original armature windings that can go wrong along with the original bearings, points, pick up brush, earth brush, slip ring, clutch components...You get the picture...

There is far more to a magneto than the condenser and plenty of other components that can go wrong....

That is why a full mag overhaul costs what it does...All these things are attended to as well....

I think if I was to use a Brightspark I would fit it to a suitably modified but overhauled mag...That is probably 'The Full Monty'...

However, I wouldn't be too keen to fit one to a mag that has no other work, or testing, carried out....That still leaves plenty of scope for further problems...Ian

Re: Magneto question

Hi Ian W,

You mentioned having starting problems with the BTH magneto...
Is it an electronic unit?

I saw a demo at Stafford last year from the manufacturer,
Peter and Maxine, and it was very impressive.

It gave a sharp, long blue spark, used no points and no power source,
And had an option of fixed or auto advance...

Are you going to replace it with the regular unit?

Cheers,
Noam.

email (option): noam10@gmail.com

Re: Magneto question

A BrightSpark condenser is a bodge, pure and simple - even the manufacturer say it has a limited life.

However, I've used them and they will get you to an event, converting something that needs a push start, to something that will kickstart.

Personally I've never had to cut/solder wires etc.
I've just fitted the cap. under the points - and its worked - which could be more of a reflection on the state of the original condenser!

Cus Andy on his Ariel, did the cutting and re-soldering thing and that worked - what it did also do was cause him to send the Mag off, over winter for a complete overhaul as he found the winding insulation was like soft toffee.
Eventually it threw the windings, locked the mag - hence the re-furb.

I've also used a BrightSpark on a good mag (trusty ES2) - it actually reduced its ease of starting - basically too much capacitance in the system (its a resonant system).

I now carry one on the bike, in the tool box - just in case.

they work, but spend money on a full rebuild if you want to enjoy riding not sweating/pushing/tinkering.

Re: Magneto question

Hi Noam..The problems are with an original BTH magneto...Not one of the electronic units...

Those are just marketed under the BTH name...(The British Thomson-Houston company were originally in Rugby, England)...

I am having an original BTH mag overhauled to a standard spec....That's still my preferred choice with either those or Lucas units...

Nigel, Interesting use of the Brightspark..I hadn't really thought of 'piggy backing' it onto a standard but failing mag to temporarily bolster the condenser...

The only problem is that the way human nature is that temporary cure is likely to become permanent, leading to the inevitable breakdown further down the road... ...Ian

Re: Magneto question

Thanks for all the reply's. The numbers and their meanings remain a mystery except the A for Anti-clockwise. I think I will send the Mag to SRM simply because I have used them before for my WM20 and it starts first time every time. They say on the webpage that after each rebuild they test for 20 min up to full operating temp, plus I had the M21 Mag (done) by a local chap for less than half the price about 18 months ago. It seems that you get what you pay for. Thanks again, Mike.

Re: Magneto question

Thanks for the explanation, Ian.

Regarding keeping the old capacitor in, "Brightspark" say:

"When an EasyCap is fitted to the contact breaker assembly, the whole magneto can function as intended,
without the old condenser interfering with the operation.
A number of people have mentioned that if the old condenser has failed completely open circuit, then there is no
need to disconnect it. That is true. However, condensers commonly fail in other ways, and it is nigh on
impossible to tell whether a condenser has failed open circuit without disconnecting it from the LT winding.
Having disconnected it, there's no point in reconnecting it again."

Noam.

email (option): noam10@gmail.com

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