NEWS FLASH - December 2013
We are now selling magneto bearings, insulators, oil seals and armature shims from our on-line shop.

Brightspark Magnetos

NEW ... Take a look at some of the equipment we use in our workshop for magneto servicing and overhauls.

 

 

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DIY Magneto Maintenance and Troubleshooting

Bearings and Bearing Insulators
Pick-up, HT Lead and Plug-cap - 1
Slip-ring
Contact-breaker Assembly
Cam
Internal HT Continuity
Main-body Earth Brushes and Bearing Insulators
Contact-breaker Re-installation and Points Setting
Low-tension Continuity
Earth Brush Continuity
Complete High-tension Continuity
Will It Spark?
Timing
Pick-up, HT Lead and Plug-cap - 2

 

Pick-up, HT Lead and Plug-cap - 1

Undo the contact-breaker centre-screw and remove the contact-breaker assembly. This disables the magneto to reduce the risk of electric shock and fire.

 

Remove the pick-up(s) from the magneto taking care not to mislay the gasket(s).

 

Check the condition of the HT lead(s) and plug-cap(s) and replace where necessary. If there is a quickly-detachable connection between the HT lead and pick-up, undo it and check the condition of the connection.

 

Check that the spring of the pick-up brush is good, that the brush is free to move in its holder and that it is not unduly worn in length or diameter. Replace if necessary. Do not skimp on quality with pick-up brushes.

 

If the brush is missing or there is only a very short piece in the pick-up, the brush (or part of it) may have come out and dropped to the bottom of the magneto housing. In that case, it it best to dismantle the magneto to retrieve it.

 

Oil on the inside of the pick-up is usually indicative of a failure of the magneto's oil seal, in which case the magneto will need a more complete overhaul. However, if the outside of the pick-up is also oily, perhaps it's all caused by an engine oil leak.

 

A lot of carbon dust on the inside of the pick-up indicates that the brush is too soft, in which case it should be replaced with a brush of the correct grade.

 

Thoroughly clean the pick-up using a rag moistened with petrol.

 

Carefully check for any cracks or pin-holes in the pick-up. If there are any, replace the pick-up.

 

With a multimeter, check the resistance between the tip of the pick-up brush and the terminal in the plug cap. It shouldn't be very many ohms, and certainly less than 30 ohms. If it is several thousand ohms, it indicates that the HT lead is resistive and/or the plug cap is fitted with a suppressor resistor. We recommend using non-resistive (copper) cable and unsuppressed plug caps. If the resistance is higher than about 15,000 ohms, it indicates a bad connection. Possibilities are:

  • the brush spring is not touching the terminal in the pick-up holder;

  • the connection between the cable and the pick-up is corroded;

  • the screw in the plug cap has gone down the side of the HT cable and not down its centre;

  • a faulty plug cap.

 

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