Magneto basics, Fairbanks Morse Magheto, no Spark

ryanwheelock · Jan 20, 2010

Working on a Lincoln Lincwelder 250 that has a Wisconsin VF4 engine on it. Think its been sitting for a lot of years but it turns over easy, has compression, all valves are working, but isnt getting spark. It has a Fairbanks Morse Magneto on it.
Have no idea what to inspection or were to start on it. Has one wire coming off it that was told from someone on the Tool Talk area that its a ground. Tried crankin with it grounded and un-grounded. Seems like I can feel something turn inside of mag. when cranking but dont think its snaping like someone told me.
Looking to find out how a magneto works, and what to inspection to see if its an easy fix or need a new magneto.
Dean, might need to buy that magneto from you but want to see if mine can be fixed first.
Going to buy a camera tonight so I can start posting pics with my questions, also Dean I'll take a pic of that mag so we can see if your mag is the same as mine.
Thanks
Ryan in Northern Michigan

Bob · Jan 20, 2010

The terminal stud can be grounded to "kill" the engine. NEVER feed power INTO it.

The MOST LIKELY problem is oxidized breaker points.

Burnish them by drawing a clean piece of cardstock through them a few times 'til they are shiny, then, with the points open, spray the contact surfaces with electrical contact cleaner and allow them to air dry "open".

DO NOT remove the mag 'til you have timing instructions at hand.
Hes a link to some GREAT FM mag info...

Dean · Jan 20, 2010

Ryan:

For proper operation, the impulse coupling must work properly. The impulse coupling is the device that you should hear clicking or snapping when you crank the engine.

If the engine has been sitting in the sun or other hot environment for long periods, it is likely that the tar insulation used on the magneto coil has melted and run down onto the armature causing drag and preventing the coupling spring from releasing the energy stored within. This will prevent the magneto from developing proper starting voltage making the engine difficult or (more likely) impossible to start.

If you do hear the coupling clicking, inspect and clean the points. Use an IBM card or piece of brown paper bag to clean the contact points. Do not use a point file.

Note: Your FM magneto has a gear driven rotor beneath the outer bakelite cover. Remove the cover carefully and be certain to properly time the gear upon reassembly. The gears should have timing marks but I advise marking with paint, etc., in case you cannot see them.

Dean

BCnT · Jan 20, 2010

simple stuff first assuming it was running when parked...clean points and replace condensor...i've seen plenty of condensors go bad from sitting.
also drain gas from tank and carb and refill with fresh once you get mag firing.
good luck

ryanwheelock · Jan 21, 2010

Thanks for the help.
I liked that website. Always like to learn the theory behind how something works before working on a new type of equpiment.
Thanks and will you guys know if I get it goin
Ryan in Northern Michigan

Magneto basics, Fairbanks Morse Magheto, no Spark

ryanwheelock

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Bob

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Dean

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BCnT

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ryanwheelock

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