Magnetos Lost spark

[Ihandy]

I have been trying to diagnose my Cubs no start issues for last few days tractor ran fine about a month ago when we had the first snow and I plowed no problems park the tractor for about a month now and now it refuses to start in the cold was working with the carburetors to no avail tried three different ones so now I've checked for spark and had no spark on the magneto so I grabbed another magneto I had that had spark at the coil and assembled that one on the cub and now it too has lost spark what is happening to the magnetos that they're dying I have filed the points set them to 13 and checked them twice all I could get was a pop out the exhaust and now nothing no spark out the coil at all please help me it's driving me nuts not to be able to plow the two to four inches of snow we're getting right now blowing and drifting

[Glen]

Hi,
Disconnect the wire to the ignition switch, on the side of the magneto if you are going to check the spark, if it is connected. That will eliminate the switch from the cause of the no spark condition.

If you have filed the points, and wiped off all filings with a clean rag, and set the gap, and the magnetos make no spark, possible things that could be wrong are the condenser or the coil has quit.

TM Tractor at the bottom of the page has new points and condensers, you could replace them first, they cost less than the new coil.
They have new coils for the magneto also.
You can look at their pictures.

If you are checking the spark the magneto puts out, they have said on here to give the spark somewhere to ground, it can damage the coil to wind the drive and make it snap with no place for the spark to jump to ground.
Plug an ignition wire in the coil post, and hold the insulation of the wire, with the metal end about 1/4" from the metal of the magneto, or the engine block, if the magneto is on the engine, when checking the spark.
The spark should jump the 1/4" gap, and be blue or white. A yellow spark is weak, and needs improving.

[Jim Becker]

Have you tried it with the grounding wire disconnected from thr magneto? That will tell you if the problem is with that wire or the switch.

I see Glen beat me to it.

[Glen]

Hi,
I didn't see that you had posted, Jim, guess we posted about the same time.

[Jim Becker]

Yours wasn't posted when I started to write my post. When I did a preview, yours was already posted. Sometimes when this happens and I haven't added anything useful, I just discard mine.

[Ihandy]

I have been testing the mags on the hood of the tractor and just by holding it not grounding it I didn't take it into consideration then it need to be grounded so maybe I ruined my mags I didn't decide to clean the original one with carb spray get the oil all off from it and I attempted to snap it again and it came back was spark right from the coil into a spark plug then it stopped again if I don't have a good enough ground at the distributor drive either is a little rusty and oily combination so my new seal that I installed about 4 years ago is leaking I'll have to clean it better maybe that will help with the grounding issues

[Rick Spivey]

If there is oil leaking into the area around the armature and filling the air gap between the armature and case, that can cause a "no spark" condition, and needs to be cleaned. That can happen from over-oiling the magneto through the oil cup, or from a leaking seal at the governor drive. The oil cup generally only needs 1-2 drops of light oil once or twice a year, based on usage.

[Ihandy]

Just to update anyone who has the same problem as I have had I ended up cleaning the magneto drive housing with a wire brush and I left out the mag gasket I had made a few years ago so I had metal to metal contact.now I have bright blue spark 1 problem solved now I've been working on the carb issues. Also I would like to note that this tractor only sat in the garage about a month not doing anything in that time we had some humid weather followed by freezing the tractor had frost all over it so that probably caused my slight rust issue thanks to everyone for the replys

[Rick Spivey]

You need that gasket to keep engine oil out of the magneto armature. That metal to metal contact is not necessary to make the magneto work correctly. I suspect you "cleaned" another issue, or possibly cleaned/set the points, etc. Often when just sitting the points will "glaze" over and you will get no spark. I suggest you put the paper gasket back in at the governor drive before engine oil causes another no spark condition.

[Glen]

Hi,
Good that the magneto has spark.

The Cub engine does use a gasket between the magneto and the engine.
Below is a listing for it at TM Tractor.

http://www.tmtractor.com/new/el/725fp.htm

Rick, I would think that engine oil leaking from the magneto drive oil seal, on the governor gear, would run out and down the outside of the engine more, if there was no gasket at the magneto mounting.

The magneto would ground to the engine by the 2 mounting bolts also.