Hi all

I need to ask that if after a rebuild, what kind of spark can be expected from a magneto

is there a maximum test gap that it can be tested to as a "pass"

Just wondering

Job

email (option): Jonnyob1@googlemail.com

Spark test


http://www.youtube.com/watch?v=UrdblID5as4



Actually, It should spart at least about 5-6mm
with a good spin, but the color is what matters.

The spark should be strong and blue,
Not red.

http://www.youtube.com/watch?v=vnqRRWuLTeE

Noam.

email (option): noam10@gmail.com

Hi John
I would never run a Lucas MO1 open circuit to see what size spark you can get. They do not have a safety spark gap built in so the voltage will build up to a level that may break down the secondary insulation and cause a carbon track which will ruin your mag. It could arc down the ends of the secondary or anywhere in the slipring/HT connection to the slipring area. Most magnetos have safety spark gaps so the secondary voltage does not build to a level that will damage the insulation they arc across the safety gap first.
Rgds
Doug W

email (option): watsond @ xnet.co.nz

hi doug,obviously you know your stuff on electrical devises,this sounds very plausible to me.
i wonder how many people may spoil a good magneto
doing just what was asked in the first post.
i have seen in the past,home-made spark ''enhancers ''
made from an old bottle top with two screws opposed to each other ,so you can adjust the gap,to make the spark jump the bigger gap,so ultimately you get a better spark at the plug?
this system was mainly talked about for two strokes i.e
villiers engines.
can you throw any light on that please ?
cheers rick

email (option): richardholt@rocketmail.com

Hello Rick,

The principle of this gadget made of bottle top is that if you take the magneto output
Directly to the spark plug, the voltage needs to build up only till it can jump over the 0.5mm gap,
But if you cut the wire in the middle and let it jump over some 2-3mm gap in the gadget plus the gap of the spark plug at the end of the wire,
The system has to build much higher tension before the spark can jump over the extended gaps,
And resulting in a better spark of higher voltage.

Noam.

email (option): noam10@gmail.com

Hi Rick, Noam, John, and all you others.
Used the spark enhancer myself with Villers and A7 Kawasakis it was useful with leaded fuel in 2 strokes to blow away the whiskers that used to form across the plug – NGK used to make plugs with the gap built in. The other trick was to lift the lead off the plug a little and let the spark jump the gap (was interesting in the wet when the spark jumped to your finger and then through you to the frame or rear of the tank!!) I have only just started working on Joe Lucas's MO1 as my M20 stopped sparking some (a lot) years ago. Mag going again and nearly ready to install. It would be easy to drill and tap the boss opposite the HT pickup and insert a pointed screw with a 6 to 10 mm gap to the slipring to make a safety gap. If you run the Mag and make the gap larger and larger the voltage will built up to ionise the airgap and spark but if there is a lower impedance path due to moisture or dirt the voltage will take the lowest path and often leave a carbonised track which will then make a lower impedance track and eventually no more sparks. With this Mag I would always carry a spark plug with an earth clip fitted so it can be tested without the chance of being open circuit with a large gap.
Rgds
Doug W

email (option): watsond @ xnet.co.nz

Period magazines had a lot of these devises and the most popular one used an old biro case with a HT lead poked in each end so you can see the spark jumping

email (option): bsansw@tpg.com.au

Thanks for the info gents

The reason I ask is that recently i had an armature rewound and took the opportunity not to have the condenser integrated within the armature

Instead I have had a brightsparx device fitted under my points holder


I have never had a mag rewound before, lucky I suppose, but I'm looking to measure performance v a normal rewind

I will fit this to my new m21 lump and will let you know on how I get on, after all, performance can only really be measured when sparking within the cylinder where fuel mixture, timing, compression, plug condition all affect operation

Basically I really just wanted to know what gap a rewound mag was capable of Jumping

Thanks for the words of caution

Best regards

Job

email (option): Jonnyob1@googlemail.com

John, I have a Bright spark condensor fitted to my 1950 ZM20 so far so good,Old condensor was knackered but the windings checked out ok !.Also be aware that most people that advertise magneto rebuilds just send of the armature to be rewound & new condensor fitted then just rebuilt your mag most of these people dont have coil winding equipment so if you can rebuild a magneto yourself you can save a lot of money by dealing direct and getting a rewound armature.The guy I use rebuilds magnetos for aircraft so you know you are getting a quality rewound armature as most mag men wont touch aircraft mags. I reckon the Bright spark condensor is the way to go as you can carry a spare points assembly with you on long trips also apart from being easy to get at the condensor is far away from heat source unlike standard lucas fitment. Dave