Cub ignition

garyandnancy · Jan 2, 2010

OK, I have a very confounding cub ignition problem. I’m working on a Cub that I have never heard run. When I crank it, it sputters but nothing will not start. In diagnosing the issue, the timing is way off, the points seem to be opening exactly when they should be closing so the spark is very late.. The tractor has a magneto type of distributor on it but an external coil has been added. I’m thinking that one of two things is wrong. Either you can not convert from magneto to coil just by unhooking the magneto from the points and installing a switch tot eh battery, wiring it to the coil, and then wiring the coil to the points. This would suggest that while coil ignition fires when the points open, magneto ignition fires when the points close.

The other possibility I have in mind is that the magneto drive is somehow not correctly installed. Right now, with the distributor/magneto off the tractor and #1 cylinder set at TDC, the magneto drives lugsslots point exactly up and down.

Ideas?

Bob · Jan 2, 2010

If you have a magneto, it SHOULD be an IH J-4 and look like this picture:

<img src = "http://www.ytmag.com/store/parts/pics/wm_R1196724.jpg">

In EITHER mag or Kettering ignition systems the coil "fires" JUST AS THE POINTS OPEN.

The mag CAN be converted to battery ignition by disconnecting it's internal coil and connecting the points to an EXTERNAL automotive coil. It's a good idea to use a condensor that matches the application of the coil you are using 'cause of variations in the CAPACITY (uF) which MAY have a bad effect on point life.

The rotor-high-tension-terminal thing gets a little weird with a mag 'cause of the impulse.

There's gears under the little cover behind the rotor that need to be timed. (I'm more familiar with the full-size version of that mag, the H-4 used on the larger tractors, someone else will have to fill you in on this one!)

For SOME information on servicing and timing the mag, cut this link and paste it into your browser:

http://www.cleancomputes.com/Cub/Blue%20Ribbon%20Service%20Manuals/GSS-1012%20Electrical%20Equipment/index.html

(This site won't allow that to be posted as a clickable link.)

El Toro · Jan 2, 2010

Where is the rotor pointing? Should be pointing to your No1 plug wire in this firing order on your cap when you have No1 piston at TDC on the compression stroke. The wire from the mag's coil should be disconnected from the points if there's an external coil that's being fed battery voltage to the points. Check to see if you're getting battery voltage to the coil. With the points open you should have battery voltage to both small termianls on the coil with the ignition switch in the on position. Use a volt meter or a test lite. Rub those poits with some 320 wet or dry. If they're pitted replace them. If you're sure you're at TDC on the compression stroke and the rotor is off you need to pull the mag and rotate the rotor so its at the No1 plug tower and then reinstall the mag. Hal
2-1
4-3

John T · Jan 2, 2010

Bob, as typical, has ya very well covered, the coil (mag or battery powered) fires when the magnetic field collapses and that begins WHEN THE POINTS BREAK OPEN. All youre doing in the conversion is using battery power to energize the coil versus a magnet rotating past it and the points still provide the current switching. The problem Id forsee is the impulse assembly in getting the timing right, but the coils still gonna fire when the points break open. That happens in a mag at near the max current flow condition to maximize the spark energy.

Happy New year yall

John T

John T · Jan 2, 2010

Bob, as typical, has ya very well covered, the coil (mag or battery powered) fires when the magnetic field collapses and that begins WHEN THE POINTS BREAK OPEN. All youre doing in the conversion is using battery power to energize the coil versus a magnet rotating past it and the points still provide the current switching. The problem Id forsee is the impulse assembly in getting the timing right, but the coils still gonna fire when the points break open. That happens in a mag at near the max current flow condition to maximize the spark energy.

Happy New year yall

John T

El Toro · Jan 2, 2010

Here's a mag that's been converted. Hal

Jim Becker · Jan 2, 2010

The other possibility I have in mind is that the magneto drive is somehow not correctly installed. Right now, with the distributor/magneto off the tractor and #1 cylinder set at TDC, the magneto drives lugsslots point exactly up and down.

I don't see a response to this part of your quesiton. If you are sure you have the engine at TDC, your drive slots are not in the right place. They should be 35 degrees above horizontal, roughly the 2-8 o'clock position.

The drive gears for the governor have timing marks but can be misengaged to put the lugs in a variety of wrong positions. With the regular battery ignition units, the distributor can be installed to make up for the problem. A magneto can not.

teddy52food · Jan 2, 2010

That mag has the wrong impulse coupling on it to work. You maybe have an H4 mag when it should be a J4. I ran into this before & found that the lugs are on different places on different couplings.

garyandnancy · Jan 3, 2010

OK, I was wondering about that. That would explain everything. Yes, right now, when the engine is at TDC on #1, the slots in the magneto are pointing exactly vertical.

So then, how difficult is it to get to that gear? Do I just remove the governor or do I need to do more?

garyandnancy · Jan 3, 2010

OK, got it figured out, it was very strange. The governor /mag drive gear was not correctly timed. Pulled of the front of the tractor and then pulled off the governor. It seems that whoever had the tractor apart did not time the idler correctly as it’s marks were way off. Not wanting to deal with the crank pulley, we set the engine at TDC on ##1 and then inserted the governor gear so that its timing mark meshed with the teeth on the idler. Put it back together and presto, it started right up. Thanks for your help.

garyandnancy · Jan 3, 2010

OK, got it figured out, it was very strange. The governor /mag drive gear was not correctly timed. Pulled of the front of the tractor and then pulled off the governor. It seems that whoever had the tractor apart did not time the idler correctly as it’s marks were way off. Not wanting to deal with the crank pulley, we set the engine at TDC on ##1 and then inserted the governor gear so that its timing mark meshed with the teeth on the idler. Put it back together and presto, it started right up. Thanks for your help.

Cub ignition

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