Cub j4 Magneto

[waynemo]

I thought my cub valves were stuck like they did last fall but now find there is no spark from the mag. I bought a new coil in December and the engine started by hand crank easily. I did not use the tractor all winter and into the spring. Last month it would not start and I thought the valves were stuck like they did last year but now it appears my mag is not firing using a home made spark testing tool and towing the tractor did not produce even a pop either!
Looks like I need to pull the mag and go through it again to see why it is not firing. Since it started and ran this spring and I ran the sickle mower with it for an hour and half just before it quit, I hope there is nothing seriously wrong! This forum will be a godsend for me to remember how to check the assembly of the coil and its component parts, which I can barely remember from when I installed the new coil. I hope it is just the points or something simple! I am 85 age with other health problems so I cannot rely on my memory! I hope to hear from you guys as how to proceed with any advice..............Thanks

[Slim140]

Take the cap off and file the contacts/points.

[tmays]

Ditto on what Slim140 said. Blow out any possible grit left after cleaning points if you use anything besides a points file. I do so even after using the points file. And recheck gap

[waynemo]

Do I have to remove the mag to clean points? I cannot remember how they are accessible.
Right now, I am working on my home made spark tool, it has a broken wire. Seems like all I do is work on my tools and testing equipment!

[Slim140]

Do I have to remove the mag to clean points? I cannot remember how they are accessible.
Right now, I am working on my home made spark tool, it has a broken wire. Seems like all I do is work on my tools and testing equipment!

It's been a while since I've been in one but if I remember correctly they are behind the piece (with screws) the cap attaches to with the plug wires. May need to set the timing on your engine and note where the location of the rotor is when you take it off.

[Waif]

With hand crank you should hear the mag click when you give it a swing.
Maybe one click per half revolution of the crank. ( So one click with a "normal" starting pull of the handcrank from six o'clock to twelve o'clock.)
It'll probably click twice per engine crankshaft complete revolution.

If you have the click I wouldn't worry about the magneto yet. Until the points and rotor and cap contacts have been checked for no corrosion ect..
As mentioned check points adjustment and condition. ( Clean looking point contacts I'll drag a clean dollar bills edge though to clean. )

If not your standard ignition stuff , then check into the coil. Then after the coil the mag..

[waynemo]

Forget about all I said about the mag. After I got my spark tool fixed I found I have good spark from the mag. So I am back to the idea my valves are stuck open since it will not pop when pulled or when start fluid is shot into the carb. This is the same thing I had last fall and managed to free them up with various fluids and oil change.
I will next pull the hood and start working on lubricating the area with the plugs removed. I have never worked on a flat head engine bu I guess the real solution is to remove the side plate and maybe even pull the hood to lube the guides, etc. I hate to have to do that! If I can get it running again, I might start it up with an aux tank of gas and let it run all day!
Any way I am glad the mag is ok and don't have to go through that again.

[Glen]

Hi,
I would test the power of the spark the magneto is making.

To do that, first lock the brake pedals together, then lock the brakes applied. If the brakes don't work right, be sure the Cub doesn't roll while doing the spark test.

Remove the ignition wire from the center post on the distributor cap, and hold the wire by the insulation, with the metal end about 1/4" from bare metal of the engine block.
Be sure the transmission is in neutral, turn the ignition switch to on, and run the starter.
The spark should jump the 1/4" gap, be strong, and be blue or white. A yellow spark is weak, and needs improving.
The engine may not run, or run right, with a yellow spark.

Do the test in a building, or not in bright light, so you can see the spark well.
The battery should be fully charged for the spark test. Charge the battery if necessary.
A low output charger is better, it may take several hours to charge it.

You can remove the valve cover, on the left side of the engine an see if any valves are stuck open.
Turn the engine and see if all the valves move up and down.
You can lube the lower ends of the valve stems with spray lube through the valve springs.