Post below suggesting an external coil on a mag got me wondering why people do that if the mags coil is bad. My tractors with mags have a H4 mag and parts are easily available and not a big deal to install. I think the mag coil is more money but not a ton more. Is there any better performance from a mag with an external coil? Doesn't seem like it to me. I bought a Cub a few years ago that had an external coil attached with a J4 mag. I repaired the mag and did away with a bunch of wiring the guy had added on for the coil and external regulator going to an alternator.
- Thread starter Charlie M
- Start date
Janicholson
Well-known Member
There is no advantage other than the idea that the external coil is a quick fix and not too technical. If the tractor is needed that day, it sure works though. The best change (though it night not be "original" is to use a engine specific distributor replacing the mag. It would adjust spark timing as a function of engine rpm, where a mag has TDC to start, then only full advance after that. Jim
DeltaSteve
Member
I once had a Regular that had a bad mag. Turned out to be a bad coil. A friend hung a battery and a used coil on the side and ran a couple of wires.I was amazed that it acctually ran!Really simple once he explained it.We ran it that way till I sold the tractor a few years later.
rlp in Co.
Well-known Member
I added a external coil to a John Deere garden tractor once when I found out that the coil was so expensive and I had several old coils from cars. I suspect that the spark was hotter than with the original coil.
One MAJOR disadvantage of using a regular external coil is now you need sufficient external battery/charging power to produce a spark. A mag can work on non battery equipped tractors and produces its own energy (not connected to nor dependent on battery) but if you use battery power to operate it (like with an external coil) and the battery is completely dead and there's insufficient charging to power it up YOURE DEAD IN THE WATER.
If you add an external coil (powered by battery) and just use the mags points as a current switch, sure it can work but you loose the advantage of a true mag that doesn't use or have to rely on a battery or charging to operate.
Similar to professor Jims note, a distributor can have an advance timing curve subject to RPM while a Mag HAS ONLY TWO TIMING POINTS Start (around TDC) then Run (maybe 20 to 30 BTDC) with no in between
John T Live in the RV from Dunnellon Florida farm days
If you add an external coil (powered by battery) and just use the mags points as a current switch, sure it can work but you loose the advantage of a true mag that doesn't use or have to rely on a battery or charging to operate.
Similar to professor Jims note, a distributor can have an advance timing curve subject to RPM while a Mag HAS ONLY TWO TIMING POINTS Start (around TDC) then Run (maybe 20 to 30 BTDC) with no in between
John T Live in the RV from Dunnellon Florida farm days
Other than a quick fix and you have old coils laying around from an old car or truck, those magneto coils were extremely expensive years ago like in the 60's. Then I think they were not available from IH for a while also.
It wasn't until several years later we could find a aftermarket source that made it reasonable to replace the coils in magneto's. We would change them over to battery ignition systems or pick through a pail of old magnetos looking for a good one.
Went through that pail many times for all those parts as it wasn't just the coil that went to heck. Impulse couplings were even worse .
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It wasn't until several years later we could find a aftermarket source that made it reasonable to replace the coils in magneto's. We would change them over to battery ignition systems or pick through a pail of old magnetos looking for a good one.
Went through that pail many times for all those parts as it wasn't just the coil that went to heck. Impulse couplings were even worse .
'
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