C magneto

hi i just acquired a 1948 farmall C and i can't get spark i adjusted the mag points to .013 and still no spark .. is there a way to test mag?is there rebuilt mags?towing the C wouldn't work, right i have a new battery and it turns over good the manual i have doesn't say much about the mag.. thanks jim

Where are you not getting a spark?

You can pull the center/coil wire from the cap and put the end otf it near a ground (the clips holding the cap on work nicely) and see if you can get a spark there. If so, you need to be looking at cap, rotor and plug wires. Try the saem test with your #1 plug wire for starters.

If you don't get a spark from the coil wire you need to work back the other direction, points, condenser and coil. First ry shining up the points with some real fine (400 or so ) wet/dry sandpaper. Some folks even use a crisp folded up dollar bill to shine them up.

If you've just got it, you may not no, but if you do, when was the tractor last running? Has the mag been taken off for anything?

thanks for the reply no spark at grounded plug or coil , the cap and rotor look like new the points look good doesn't look like the mag has been off and i know the guy i got it from and he said it was running 3 years ago.. if someone jumped it wrong with 12 volts cable and wrong ground would that wreck the mag i asked him if he did and was hesitant.. i took the ground wire off the mag and still no spark.. it has me stumped first mag i ever worked with jim

A magneto is a totally self contained ignition system. It is totally independent of the tractor electrical and charging system, and is not supposed to even be connected to anything else. Jumping the tractor from a 12 volt battery will not affect the mag, nor would jumping from a 6 volt system. Positive ground or negative ground makes no difference to a magneto.

A bungled jump start (12/6, reversed polarity . . .) shouldn't be a factor with your problem. The mag is an isolated unit, totally independent of the rest of the tractor's electrical system.

It could be a weak magnet, but it's more likely your problem is going to be coil or condenser. Either one will require removing the mag, so all the precautions of having the motor set up at TDC on compression on #1 before removal (and then not disturbing it) will make the job less prone to problems when poutting things back together. Both the coil and the condenser will require removing the rectangular cover on top and the cover on the motor side of the mag. Handle the two insulators for the stud on the condeser carefully (the little brown ones, one inside, the other visible on the outside around the connection for the ground wire), they're not easy to come by.

Before getting into that , please do try shining up the points, they'll look good but a little corrosion on them will keep yo from running.

One other pesky little thing that pops up now and then, too, is a short from the wire between the consenser and the points where it passes though the distributor body. That's be worth a look.

Worse comes to worse, you can have it rebuilt or swap it as a core for one already rebuilt. If it comes to that, I've heard good things about the shop at the link below. Theres' also Magman, but his link isn't working. Maybe someone else will have a way to contact him.

Good luck and come back for more if we can help. Theres' better hands with mags than me around here.
Mainely Magnetos

When I bought my C 30+ years ago it had a mag and the same problems. My advice is to go to a bone yard and get a battery/coil distributor and replace it. I think the same distributor fits a lot of the letter series Farmalls. I had a IH dozer with a mag and the fix there was to go to battery/coil too.

A little bit of sandpaper through the points and a new condenser. Cond. will kill your spark. Napa will have them.

hi cleaned points checked gap etc,, if i turn it over i have no spark from mag to dist cap and vice versa.. even if it was the points condenser etc shouldn't i have spark in wire from the mag ,,, spark goes from mag to dist cap right??

Nope, it can't make the spark if any one of the points, condenser or coil aren't working.

The magneto concept is only slightly different from that of the battery ignition. The only difference is the source of the armature rotating inside a field to generate the juice. It's internal to the mag, which has a permanent magnet in its shaft. On a battery ignition with the external coil, the permanent magnet of the mag is replaced by an electrically induced magnetic field, an electromagnet, instead of a permanent magnet within a coil.

All of this is overly simplistic, but is, I think, close enough to address your question.

Basic misconception is that the spark happens when the points close to complete a circuit.

The way it actually happens is that while the points are closed, completing a circuit to ground giving the generated electricity a path to flow, the coil is building a charge in the field between the magnet and the coil. The spark occurs when the points OPEN, causing that field tocollapse, releasing its energy to the coil wire to be distributed through the rotor and cap to your plug wires. The condenser is there as a kind of electrical shock absorber, so that the energy doesn't flow back through your points, which would keep the charge from building up or, once it's released, flowing back through the points instead of the coil wire, which would smoke the points in VERY short order.

So . . .
1) dirty/corroded points will deny the whole works a path to ground to build a charge in the first place. There will be no field there to collapse when the points open.
2) a faulty condenser will keep the charge from building by not dampening the flow back to the points, or will fry the points.
3) a faulty coil will not respond to the stimulus of the magnet spinning inside it and will not be generating a charge in the first place, rendering the points and the condenser irrelevant. By that same token, going back to my earlier post, a too-weak magnet wont be enough to stimulate the field within the coil, either, but the magnet might be the last thing to look at.

Hoping this makes some sense . . .

The condenser is a shock absorber and with its wire off you can check for spark. If the condenser is shorted out it will act the same as the ignition switch to a magneto which just grounds out the points. I would also remove the ignition wire from the points for the test as well. The ignition wire has been known to ground the points where it goes thru the case. I like to do all of those tests in a vise rather than on the tractors. It makes it easier to snap the magneto over to check for spark. That could bring up a timing question for some. It sure can be done

If you do not get a spark at the points with the condenser and ignition wires unhooked when snapping over the magneto you then have either a coil or armature/field problem. Probly coil. I did have a magneto last spring where both the field and armature had lost its magnetism.

i have the points clean and set so i will replace the condenser and try that i don't understand about the coil on a magneto system it is inside the magneto? if i take the rectangular off the magneto can i see the coil or is it inside the magnet to take magneto off tractor, get on top dead center and remove the whole assembly with the cap, mag etc

Ye, you'll be able to see the coil with the rectangular cover off.

To do the kind of testing that DickL described (an excellent way to analyze where the problem might be), yes you want to take the entire mag assembly off the tractor. It's before that that you want to be set up on TDC on #1. Your question kind of ran together, so I'm not sure if you were asking about how to set it up that way but if so, let us know, we can get you there.

i have the cover off for the flywheel, but i can see any marks on it i can't see any pointers on pulley on crank in front what is the best way? thanks jim

Should be a pointer at the bottom of the flywheel.

If you take the valve cover off and watch the rocker arms for both valves on number one to just close the knotch will be very close. Within a coupla inches. Number one will always be to the front. The front being that part of the tractor breaks the wind when in road gear.

The mark on teh flywheel can be divilishly hard to find. The other method that will get you close enough for government work is to pull all your plugs. If you have a hand crank, great, useit. If not bump it on the starter and finish up by using teh fan blade to turn the engine.

Where you want to wind up is on the upstrooke of the #1 (front) piston. You want the compression stroke, so you will be able to feel it pushing air out if you jam your thumb over the plug hole. Keep turning the same direction (clockwise when looking from the front) until you can see the piston come up as high as it will go, looking through the plug hole with a light. When it appears to be about the top use a skinny screwdriver or a 6" piece of stiff wire. Put the tip of the screwdriver or wire through teh plug hole so that it rests on top of the piston. Then use the fan to rock the motor back and forth until the handle or the end of the wire is at its lowest point. That will happen when the piston is at the top, which is where you want to be.

If you pull the cap on your mag, it should be pointing to the #1 plugwire, which is an important piece of information for when you analyze things and go to put it all back together.