Mag vs distributor

Will a tractor start and run as well on a F4 mag as a distributor? If so why did IH as well as all manufacturers switch ?

It might have been simpler to build and maintain.

It's cheaper to build a distributor. A properly tuned magneto is a very reliable system, and has several advantages, particularly if the battery is not up to snuff. Three of my tractors have distributors, four have mags, and they all work goo and start easy. One has an electronic conversion on the distributor and it is noticeably better as far a fouling spark plugs.

A battery ign unit gives you a variable automatic spark advance. In other words, with the engine running at slow speed you have zero spark advance and when you speed the engine up the spark advances gradually in relation to engine speed. This is controlled with weights and springs,. Each battery ign unit have a maximum advance limit. Most original equip battery used on the letter number IH tractors, ign units were 40 degree units so as you increase engine speed the spark keep occurring earlier in the cycle up to the max limit which should occur at rated engine speed. With a magneto, the spark is retarded (lag) so at cranking speed the spark occurs at or just after top dead center. That is what the impulse coupling does. Of course it also give mag that extra zip for hot spark at cranking speeds. Once the engine starts the spark is fully advanced. Most are about 35 to 40 degrees before top dead center. So, you see, even at low engine speeds the spark plug fires those 35 degrees before that piston gets to the top. This is too early for slow speeds but they get by with it if engine is not working hard at that speed but it makes the engine run less smoothly. Gasoline needs time to ignite and that is why you have to have a advance in timing as engine speeds increases. You always want that charge to have maximum push on piston when piston is going back down, not still coming up. Magnetos have the advantage that no external battery power is needed to run an engine. Some older tractors had a spark control lever to adjust the timing of spark and that was operator controlled.

that and the faster you turn a mag, the hotter the spark gets........plus all the goodness already stated about mags.

Battery ignition is much simpler than a mag, and fewer moving parts. However, needs a battery and charge in the battery.

Personally, I prefer mags. If they are right, no matter how cold the temp is or how dead the battery is, they work.....but they require a bit more attention that a battery ignition system.

Many things come into play on a question like this. The first tractor built where hand start since battery starters had not been made so they had to have mags. Then as technology got better the distributor was dropped since it cost less to make and did the same job and then of course there are many other factors that come into play

they actually start better with a mag, as you don't have to spin the engine over. also don't need a battery. most magneto tractors from the start were hand crank. that's the advantage as the engine started with only a slow turn of the crank.
something like the old ford's verse chevy's. the chev would start with basically a dead battery but as long as it give the engine a flip it would take off. while the ford if it was not cranking fast enough it would never start.
everything is obsolete now as tractors are computer controlled.

Probably because by the time IH started using distributors most people wanted a starter so a battery and charging system would be getting common. Also a distributor offered better performance between idle and full throttle at a cheaper cost on a tractor already equipped with a starting and lighting system than the IH magneto did. Also around that time lots of farmers started wanting more power and manufactures started trying to supply them.
IH did offer the magneto as a option at least close to a decade after equipping them with distributors.

I'm thinking since your handle is "Farmall A" that you mean an H4 mag???

F4 mag...

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