Thu Feb 14, 2013 4:11 pm
Had problems getting 49 cub to start. Found I had wrong magneta. Bought a new rebuilt mag from a member. Can't get it to start, seems to have good spark.
Upon checking with an vtom meter the stud on the mag that the kill switch wire goes to is grounded to ground.
Is this normal? I removed the kill switch wire from the mag and the stud checked grounded.
Thu Feb 14, 2013 4:22 pm
AAm wrote:Is this normal? I removed the kill switch wire from the mag and the stud checked grounded.
Thu Feb 14, 2013 6:25 pm
I begin by admitting my limited knowledge of mags. Fifty years ago, as a young boy on the farm with my dad I spent many hours on a mag fired Allis. However, I remember the ground/kill lever on the mag. On the Allis, you had to get off the tractor and go over to the mag and pull the lever on the mag to stop the tractor. Apparently the Cub has a stud which you can connect a wire to and then the wire to a remote ground/kill switch. This gets me to Eugene's response. Unless I am missing something here, I do not think a continuity check of the stud to the mag body should indicate a closed circuit. I would expect the test to indicate an open circuit. If it is closed I would suspect the insulation around the stud or the lead from the coil must be grounded internally to the mag body somehow. What am I missing here?
Thu Feb 14, 2013 7:38 pm
challenger wrote:This gets me to Eugene's response. Unless I am missing something here, I do not think a continuity check of the stud to the mag body should indicate a closed circuit. What am I missing here?
High tension magnetos, the stud/kill switch wire location is typically wired into the magneto's primary circuit. When the switch on the dash is in the run position - it's open. In the kill position - shut off the engine - the switch is in the closed position.
Primary circuit includes a direct connection to the condenser, the points when closed, and the primary winding in the coil. The primary coil winding is grounded on one end - kill switch on the opposite end.
When checking the kill stud on the side of a magneto - it will show a ground. Having said all that, different magneto manufacturers internally wired their magneto a bit different. Basically, the kill switch grounds out the magneto's primary circuit.
Thu Feb 14, 2013 8:35 pm
Eugene: Thanks for the explanation and education. I have three Cubs (so far) and none have a magneto. I would have liked to have had at least one with a magneto so I could have taken it apart to refurbish and familiarize myself with the internals. Learning by doing is the only way I have obtained my limited mechanical knowledge.
Thu Feb 14, 2013 9:03 pm
Not my usual auto parts store. Struck up a conversation with old guy behind the counter as I ordered brushes for my 154's generator. Old guy is into antique tractors. He said that the first thing he does with a magneto is remove the internal coil and install an external coil.
Edit: Most small engines have some sort of magneto ignition system. Principals are the same. Internal wiring, often a bit different.
Thu Feb 14, 2013 10:08 pm
You said it seemed to have good spark, so most likely it is not timed right. A magneto can be installed 180 degrees out of time quite easily.
Fri Feb 15, 2013 1:52 am
THE PRIMARY IS BUILT INTO THE MAG. ROTOR====THE SECONDARY IS WHAT
IS ON TOP AND THIS IS WHAT YOU GROUND OUT----WITH A EXTERNAL
COIL YOU HAVE A NEW PRIMARY AND SECONDARY SO YOU GET A REAL
Fri Feb 15, 2013 11:30 am
I am glad to get schooled on mag's performance but dissipointed that I didn't have a solution to my problem.
I have watched the vidio in the How-to section on how to time the mag. I think I have it timed right.
Sure wish I had it at the DSCF today. I know that they could get me on the right track. Have fun guys.
I will be close by tomorrow as I am going to St. Augustine on Sat.
When I get back I will go at it again. This time will attack the carb.
Fri Feb 15, 2013 7:58 pm
http://www.cleancomputes.com/Cub/Blue%2 ... e%2040.jpg
Above link has a simplified wiring diagram for the IH H-4 magneto. Once tractor is running there are two ways to kill the engine. 1) Is to ground out the secondary winding so that spark does not reach the spark plugs. Or 2) Ground out the points - essentially bypassing the points - grounding out both ends of the coil's primary winding.
Sat Feb 16, 2013 11:44 am
Here is a diagram of a magneto similar to what is used on International tractors, as well as most others. It is not the best in that the 2 circles at the top where the primary and secondary windings leave the coil appear to be connected. In reality they are not connected to each other, they were just drawn too close together.
Sat Feb 16, 2013 1:37 pm
Using John's posted magneto wiring diagram. The stud/post on the side of the magneto for wire leading to the kill switch is located in the circle to the left of the flag at the indicated ignition switch.
Back to the no start problem. Two possible areas to check.
1) timing of the rotor under the distributor cap.
2) timing the magneto to the engine.
Sat Feb 16, 2013 7:34 pm
YOU ARE GOOD WITH THE P.C. MAYBE YOU COULD FIX IT AND
THEN RUDI COULD PUT IT IN HIS MANUAL`S -------IT IS A
Sat Feb 16, 2013 10:02 pm
That diagram is part of a course offered by a university in India (IGNOU), and the diagram so far as I know is there property. I should have given credit to them for it in the posting. Here is the .pdf for the course.http://www.ignou.ac.in/upload/unit%204.pdf
Sun Feb 17, 2013 8:07 am
Just keep in mind (if the indicated rotor direction is correct), that the firing order depicted is NOT for a Cub. If the rotor direction is reversed, the 1,3,4,2 shown would be correct.
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