checking the magneto

T

thefairlaneman

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Before I spend any real money on it I want to determine that the magneto is working The wiring harness has been removed because its falling apart and cracked up but can I check the magneto by just runing a hot wire directly from the battery and then see if its throwin a spark to each plug? I assume theres no ballast resistor. ? thanks
 
JB

JB

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Re: checking the magneto

You are not going to get much response without telling us what engine you are dealing with, fairlaneman.

If it is really a magneto it needs no battery. Magnetos make their own volts.

99
 
L

Laddies

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Re: checking the magneto

If you run 12 volts to the mag you will fry it just diconnect the kill wire from it and turn the engine over
 
Scaaty

Scaaty

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Re: checking the magneto

Probably spitting in the wind here..but with a Mag, there is no such thing as "putting 12volts to it"...owned too many old HD Sportster's with Mags. Batt. if any, was only for lights, start if it had one, and the Generator.(THAT needs a "flash")..has ZERO to do with Mag Ignition

Suggest a internet search, of "How a Magneto Works".....
 
T

thefairlaneman

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Re: checking the magneto

The engine is a 1960 merc 300....Question is How do I check the magneto to see if it is working? thanks
 
L

Laddies

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Re: checking the magneto

Just remove the spark plugs and crank the engine with the kill wire off, either with a rope or jump the starter.
 
T

thefairlaneman

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Re: checking the magneto

I cut the wire running to the magneto and spun it with the starter. At the same time I put a bolt into a spark plug wire and looked for an arch to ground.(I checked several of the plug wires to rule out a bad wire) no spark! It worked years ago so I guess the next step is to take the magneto off of the engine and start looking inside for problems.I will be ordering parts soon and am trying to get them all at once. thanks Good news is it has good compression on all 4 cylinders ( 95 /100 lbs)
 
JB

JB

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Re: checking the magneto

There are two magnetos in there, fairlaneman. One for each cylinder. They use in common the magnets in the flywheel and the points cam. That is all.

It is possible that each has its own problem, but I would confirm that the common parts are working first. Check flywheel key, points cam.
 
L

Laddies

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Re: checking the magneto

JB, sorry but it's a single mag probably a Kiekhaefer model 4D, Fairlane if your not a magneto man you really need a manual, you can remove the kill wire and the 4 bolts holding the mag to the swivel bracket, drop it down carefully and remove the ground wire and cap then with the mag off the engine remove the rotor with 2 screwdrivers careful it's about $90 then off with the mag cover and your to the points there about $40 replace them and the cond and if the coil is OK your good to go. Also if the cap and rotor are red or green in color they probably won't run right and will need replacing also. Good Luck
 
T

thefairlaneman

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Re: checking the magneto

Update. I removed the mag and the top rotor assem.......and very carefully the rotor.......I then cleaned with 600 emory paper all of the cap terminals and points. A small hairline crack in the rotor cover near a bolt hole was reinforsed with some epoxy to keep the crack in check. I will replace the condensor with another one that should work to rule out it being just a bad condensor and then put it back together and back on the engine if I have no spark then I will go ahead and order a new coil...Not much differant than some lawn mowers Ive worked on so far.
 
Yepblaze

Yepblaze

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Re: checking the magneto

What might be quite important is that the points are TOTALLY free of pitting, faced square to each other, and set at .008-.010"

And that does not mean dragging some sandpaper through them, as that only fills the "pits" with crap, screwing it up.

If you want to service and reuse the pointset, remove and dis-assemble them. Then with a small file, file them perfectly smooth and square to each other.

Use a magnifier to see that all pitting is removed.
 
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