Author Topic: How to test condition of the magneto SR coil  (Read 7181 times)

Offline BlueT21

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How to test condition of the magneto SR coil
« on: April 18, 2011, 06:19:06 AM »
Hi mate!

currently i am overhauling my spare lucas SR becoz too small spark which the engine cant start..does anyone have an idea how to test the electrical characteristic/condition beside of Insulation resistance test ? what is the preferred value of ohm ?

thank you in advance
cheers.


Offline R

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Re: How to test condition of the magneto SR coil
« Reply #1 on: April 18, 2011, 07:42:52 AM »
If you have a spare SR, can you measure the ohms of this spare and of a good magneto as well ?
Ultimately, if it doesn't produce a sufficient spark, time for remedial work...

Not where I can test one, sorry. Anyone ?

Offline Rex

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Re: How to test condition of the magneto SR coil
« Reply #2 on: April 18, 2011, 09:03:54 AM »
I almost hesitate to answer another mag thread question... ;)

It's not really about the resistance per se, but more about the coil/cap failing after 60+ years, sadly. If the "small spark" isn't down to other things like the points, plug etc, then realistically (as above) you're looking at a rewind and new capacitor.

Look on the bright side, though; after the overhaul it'll probably be working long after you're gone... ;)

Offline Revband

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Re: How to test condition of the magneto SR coil
« Reply #3 on: April 18, 2011, 11:05:10 AM »
Hi Blue

The SR series of mags are one of the most reliable and easy to work on.

The resistance measurements should be, Primary coil 1.2 ohm, secondary coil 5k ohm (this is measured with an Avo model 8 analogue meter, other meters will give a slight variation), the capacitor is easily eliminated as this is a separate unit which is easy to replace, however if the coil is the original one you should seriously consider having it rewound as the insulation and wire used will be in poor condition by now, the rewind on these is relatively cheap as it is a moving magnet rotor the coil is a separate unit easily removed and rewound.

If you have the unit stripped for any length of time wrap an old chain round the rotor to act as a keeper.