Magneto Timing Problem

[Potatoman]

Hi all...New to the forum.

Wasn't getting any spark in my Cub. Plugs looked fouled, so I replaced those, but still no spark. No spark at magneto.

Removed the mag, cleaned and shined rotor and coil connector and got spark. But when I went to reinstall it, and set the flywheel to TDC, the mag won't line up with the governor. The mark on the flywheel doesn't line up with the pointer, either. It's at the very top (dead center?) of the flywheel.

I'm guessing it was always slightly out of time. Only had it a few years..

Anyway, I'm unsure how to proceed. I'm thinking about moving the rotor to #1 position after lining up the mag, but would I need to adjust the points too?
Or should I just tear it apart and adjust the flywheel and governor?

[Eugene]

OK. When the pointer and the TDC mark line up on the pulley, a piston, either cylinder #1 or #4 is at TDC.

Check for compression on #1 cylinder, finger is spark plug hole. When you feel compression , slowly continue rotating the engine until the pointer and TDC mark line up. Then install the magneto.

[Potatoman]

That's what I did...but the #1 cylinder starts compression (and the magneto is set to fire #1)..the mag dogs won't line up with the governor

[Rick Spivey]

At TDC the governor dogs should be at roughly 2:00 and 8:00 as viewed from driver seat. I suggest you readjust governor as needed, because it is very difficult to time a magneto when governor is mounted incorrectly. I don't suggest you start taking the rotor out of time, it needs to line up with marks aligned to pinion gear. If the governor was 90 degrees out or some other multiple, no big problem, but if it is one or two teeth off, I have never been able to "fudge" a mag to run correctly. It is not as flexible as a distributor.

[Potatoman]

That's what I was afraid you were gonna tell me, but it probably is the best way to proceed.

I saw another post here where someone said you can just crack the governor and advance a tooth a time. I took out the two bolts on the side opposite the mag, but I don't have access to the gearing. Do I just rotate the dogs to jump a tooth?

[Eugene]

What is the history on this engine - tractor? Has the engine been running since you have owned the tractor?

[Jim Becker]

If you have been using the tractor for several years, it is unlikely the governor is out of time. Gear mesh just doesn't change by itself.

You keep mentioning flywheel. Are you talking about the front pulley or are you really looking at the flywheel on (possibly) another model tractor? Let's get on the same page. A cub engine is at TDC when the notch on the front pulley is aligned with the pointer on the left side of the front cover. If there are two notches, use the second one to reach the pointer. In this position, the slots on the governor gear that engage the magneto should be at about 2 and 8 o'clock.

[Matt Kirsch]

IIRC, the front pulley is keyed to the crankshaft, so if it is installed properly, the mark HAS to line up with the pointer at TDC.

If it doesn't you have one of two problems:
1. You are not at TDC (most likely).
2. The front pulley was installed without a key.

It's not at TDC when it starts pushing air out. That's just the beginning of the compression stroke.

Easy way to tell if it's at TDC on compression is to put your thumb over the spark plug hole and turn the engine until it starts pushing air out. Then you can drop a long thin screwdriver down the spark plug hole and rotate until it reaches its highest position.

[Potatoman]

Okay...I realized I was mistaking TDC for the start of the compression stroke. So when I turn the engine from the start of the compression stroke to line up the notch on the fly wheel everything matches up. After re installation of mag, when I turn the engine by hand I hear the second click right on the pointer mark.

Still won't start though. Seems to fire once or twice, but no start.

The spark at the plugs doesn't seem to be as strong as the spark from the coil (new wire and plugs). Rotor or cap?

I've had to fix 560 (carb), I300 (solenoid), and AC G (wires) already this year, but this one has me stumped

[Potatoman]

Oh...and the tractor does have a history of being tough to start, and quitting when hot, then starting when cooling down. That's why I figure it's the mag

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

Did you use copper plug wires, and not carbon wires, mags do not like carbon wires for some reason. If it is firing once and the starter kicking out, that is a sign of a weak mag coil. It can be other things, but every time I have had it the coil turned out to be the problem. Your post about being hard to start and quitting when hot also points to a bad coil, or occasionally a bad condenser, but the coil is the more common problem, also by far the more expensive one. If you happen to have an extra 6 volt coil laying around it is easy to convert the magneto to a battery ignition for a test before spending $65 for a new coil.

[staninlowerAL]

Removed the mag, cleaned and shined rotor and coil connector and got spark......I'm guessing it was always slightly out of time. Only had it a few years...

Is the rotor and pinion gear timing marks matched? For the service manual on the CUB J4 mag look up GSS 1012 Electrical Equipment, page 4 will tell you all you need to know about removal/service/maintenance/installation. That way you won't be guessing about what you have or what needs to be done. Available free download pdf format at "QUICK LINKS" Tab top left corner of this page.

[Rick Spivey]

So if all lines up at TDC, then maybe the wires (or some of them) are crossed. Not questioning your skills, just saw that mag was removed, so always possible (no matter how smart I am). Also some symptoms do sound like coil, as suggested by others. Lastly the pinion and rotor are match marked (or should be). Look for a cast line on rotor, and dot or triangle on rotor. If all is in time, and plug wires are 1,3,4,2, then I'd bet on bad coil. As a purist I prefer to fix the magneto, so it operates as it should. An external coil will get you running, but is the worst of all worlds in my opinion. Or for the same price as a coil, you might could locate a complete distributor. But with distributor or external coil, you have to keep 6 volt battery on board and charged. A magneto needs no battery. Your call.

[Potatoman]

Put new copper wires on and checked the rotor is properly aligned. I'm getting good spark from the coil, but maybe that (or the points...which I didn't check) are the problem

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

If you are getting a hot spark from the coil the points are working.