47 farmall cub no spark

[dambrino1]

Hey guys,
Been reading a lot on here lately, trying to figure my problem out. had a float charger on the cub for a while to maintain the battery. last week, went out and the battery was exploded! blew the top off. bought a new 6v battery, and now no spark of any kind. i replaced the capacitor but dont know why, i just did it. any ideas on what to look for?

thanks!!!

[John *.?-!.* cub owner]

distributor or magneto?

[staninlowerAL]

Regarding John's post, Does it look like this?

dist1.jpg (31.79 KiB) Viewed 533 times

Or like this?

[dambrino1]

bottom.

[staninlowerAL]

So your dealing with a magneto. If everything is up to spec you don't even need a battery for the tractor to run. Try turning the engine with the center wire removed from the distributor cap and held about a quarter of an inch from a good clean ground. If you don't see a good spark, it's time for a magneto rebuild to include a coil replacement. There's a few forum members who do this and it takes special tools to disassemble it to keep from damaging it. You could also upgrade to a battery/distributor ignition system or substitute an external coil for the magneto coil but that's another subject.

[dambrino1]

thanks for all of the replies. where i'm stumped, is that it ran fine before the battery exploded.....the mag is new, but i assume that something could have shorted when all this happened.

[Bob McCarty]

Did you check/replace the points?

Bob

[dambrino1]

going to do that today. if no spark.....coil?

[Glen]

Hi,
You could replace the points, I guess you replaced the condenser. Sometimes a new condenser is defective and doesn't work.

[ricky racer]

As staninlowerAL stated, the magneto is totally independent of the battery. I suspect it might be the switch on the dash could have shorted out possibly someway. Remove the ground wire on the outside of the mag (bottom wire on the picture below) and see if it will start.

[dambrino1]

Yes sir, i have already done that. nothing. also looked at points while turning engine over. nothing. i'm guessing that it might be the coil now. replaced the condenser already.
I did have a question about that though. the lead from the condenser, as well as the lead from the coil go to the same post next to the points, but is there supposed to be something separating the two? i have them both together.

[staninlowerAL]

It's like Ricky said and I alluded to in the earlier post, the magneto is totally independent of the battery. If you will download the BLUE RIBBON SERVICE MANUAL GSS 1012 from the MANUALS link above it will help you understand what's happening. Basically when the magneto shaft is rotated, the wire coil of the magneto is excited by the motion of the magnet rotating inside of it. The electricity produced by this motion is seeking a ground so it will go to the most readily accessable (read least resistance) ground which is normally through the points when they are closed or to the sparkplug when the rotor is aligned with that point. If you provide a ground for the magento coil wire to distributor to jump to a metal ground it should jump there as well. That's why a magneto will shock you if you hold the coil wire, you become the ground point. The mag does not even have to be attached on the tractor for this to happen. The coil experts recommend not rotating the mag shaft (and producing the charge/spark) without somewhere for the discharge to go to because you run the risk of the spark seeking a weak insulation point and burning the wire in the mag coil. Wordy, I know but maybe that helps. Stan

[Glen]

Hi,
Here is a page from the Cub owner's manual showing the magneto points and condenser.

http://farmallcub.com/rudi_cub/www.clea ... age-28.jpg

[dambrino1]

took the magneto off and i rotated the mag while on a vise, looking for any sign of spark. nothing. I completely disassembled it as well. the magnets seem to have good magnetism, very little light oil on them, and very clean. when i mounted the coil back, i (purposely) put my finger on the discharge nub on top of the oil (cover off) and gave it a spin. the was a little jolt on my finger but not near what i was expecting. could that be the problem? should i have really got zapped? weak coil perhaps?

[Jim Becker]

. . . gave it a spin. . . .

What you did should have given you a good jolt. Giving the magneto "a spin" should be difficult. When you try to turn the coupling it should bump up against a stop. Continued rotation should load up a spring. Then the stop releases giving the magneto armature a rapid turn. If it isn't doing that, you will not get much spark. In that case, the impulse coupling needs repair. Otherwise, the problem is points, condenser or coil.