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Magnetos, Ignition Coils and Spark Plugs Discussion about magnetos, buzz coils, spark plugs, ignitors and low tension coils.

Magnetos, Ignition Coils and Spark Plugs

farmall H 4 magneto impulse coupling

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Old 08-26-2015, 05:53:16 PM
mshm99 mshm99 is offline
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Default farmall H 4 magneto impulse coupling

I've been lurking for a while.This is my first post.So I have what I was told a '42 farmall H. I bought in '91 . I bought it to work a few hours a year mowing ,plowing ,general work and food plotting for deer. Well the truth is that it has been the most trouble free piece of equipment I own. I have not had to do anything but grease,oil and gas this gem. I grew up with B's A's and G's so tricycles never scared me. Any way this spring the H did not start. No spark. I knew nothing about magneto's except when my uncle had hold a wire,and I learned there was fire in that thing.(note to self) And they either worked or they did not. I had no idea there were points in there,and so I never gapped them. So by the time I figured that out and got to the points there was no gap.So I gapped them. Well it started but faded fast with weak spark, then quit after about 10 minutes of running on 3 cylinders. So I figure points ,plugs ,rotor,etc. It's past due. So I'm seeing how to static time it, and I do not hear that sharp snap that should be happening. So that brings to where I am today. The impulse coupling. I can say for sure the springs are worn out. As you can see from the picture I need a little more info. So if some could lend some guidance I'd be grateful.

Mike in Illinois

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Old 08-29-2015, 12:32:20 PM
mmcdonald mmcdonald is offline
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Default Re: farmall H 4 magneto impulse coupling

Stop pin could be worn. It is full round originally. If it is worn you can press it out, rotate it and press it back in, so wear area is not where trip fingers contact anymore. Those springs on the trip arms/weights are good but not 100% crucial to it working. The faster the engine turns over the more important they become to help keep arm extended to catch pin. The drive plate is on a taper. There are threads inside the hub for a special puller which is what we use. It generally takes a good bit of force to remove it and I have not tried it any other way. It is conceivable that you might use a standard type puller but since I have not done that I will not advise it. Coil is made of two windings, a primary and secondary. Both are grounded on side of coil we can't see in the picture. New ones and some old ones are a thin metal strap that is affixed under the coil mounting screw. I have also seen them soldered. The primary ungrounded end is the one that attaches to the condenser. The secondary ungrounded end is the metal button that contacts the cover cap. Hopefully this helps some. Good luck.
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