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Checking H4 magneto model interchange

Crazy Horse

Crazy Horse

Well-known Member
My friend has an IHC magneto repair manual. It says the H4 mags with NO letter after the numbers are for models A,B,H,M,W4 and W6. Does that make sense? For example something like H4-3547603 might be a mag serial number that works on all that stuff. These have a drive plate clockwise rotation when viewing from the front of the tractor (or when viewing the drive-plate when the mag is off the tractor).

Other mags for other models have a similar serial number setup but there is a letter after the numbers, like maybe H4-3547603 D (or something like that). These have a counter-clockwise drive plate rotation when looking from the front of the tractor (or looking at the drive plate when off the tractor).

Am I interpreting this information correctly? And are mags from all those models I mentioned without the letter at the end interchangeable between tractor models?
 
All H4 mags with clockwise rotation will fit all the letter series tractors you mentioned, except for the Cub. All H4 mags with counter clockwise rotation fit all gas start diesel tractors. Both will physically fit in either or, but if you turn one over with the wrong rotation mag installed you will ruin it.
 
OK, thanks for that information. I have a mag here that came off a model H and I want to try it on my Farmall A. Supposedly, the mag from the H works good but when it gets hot after operating for a while, it shuts down. Maybe a condensor? I'm no mechanic but someone told me that a bad condensor on a battery ignition/distributor system will shut down or give problems when heated up. Thought I might ask you since you seem to know what's up with those mags.
 
Maybe ruin was the wrong word, but they are not designed to be turned backwards at cranking speed. I am quite sure you knew what I meant.
 
An H4 mag can be made to turn either rotation. you need the correct impulse, points housing, and have to move the impulse pin. However, the internals of the H4 stay the same. It is not a 2 minute conversion, but the core parts of the H4 are identical regardless of rotation.

No damage or harm turning it in the wrong direction.
 
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