1948 Cub Ignition

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Re: 1948 Cub Ignition

Postby Eugene » Sat May 03, 2014 11:17 am

jimpitz wrote:In addition could this whole assembly be replaced with the IHC breaker point system?
Unless this is going to be a parade, trailer queen, I would use the current ignition system, as is. The current system is quite functional.

I'm not sure how you are checking the ignition system for the fault(s). Suggest checking for battery voltage, magneto points open, starting at the magneto and working back to the ignition switch and beyond towards the battery. Once you find battery voltage, the problem will be in the previous appliance or wire checked.

Edit: Ignition system fires when the points open. In the above described system problem diagnosis all you have to do is roll the engine over by hand until the pulley TDC mark is a bit, a smidgen, after the pointer. This will open the ignition points.
Last edited by Eugene on Sat May 03, 2014 4:04 pm, edited 1 time in total.
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Re: 1948 Cub Ignition

Postby John *.?-!.* cub owner » Sat May 03, 2014 3:34 pm

With ignition coil (not internal mag coil) you should have voltage to ignition side of coil anytime switch is on. Side of coil going to distributor/magneto should have NO voltage when points are closed and battery voltage when they open, which means that when engine is cranking over, on the distributor side of coil you should see voltage come and go rapidly, 2wice per revolution of engine.

Note, on a magneto fired engine (no external coil) the switch only has one terminal and does NOT provide power, but instead provides a ground to kill the spark. Also, if your battery is 6 volts, positive ground, the + terminal of the coil goes to the magneto/distributor, since that is the side that gets grounded, though it normally will run either way.
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Re: 1948 Cub Ignition

Postby Posco » Sat May 03, 2014 10:37 pm

After getting no fire from the external coil I hooked up today I went back and pulled the magneto coil this evening and found quite a bit of oil on the rotating block that lies beneath it. Those magnets are incredibly strong BTW. I don't know if that would inhibit anything or not but I cleaned it well and hooked the magneto coil back up again. I also removed the terminal from the side of the distributor and made sure those were clean and free of corrosion/contaminants. Confirmed pinion gear and rotor timing. Confirmed gap on points.

Also confirmed timing once again at TDC on #1 cylinder. Impulse coupling snapped/tripped as I rotated the distributor away from the engine block. Secured the distributor there. Installed new plug wires and distributor cap and looked over all of the wiring for loose connections and frays. All good there.

I'll try firing it in the morning. Wish me luck.
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Re: 1948 Cub Ignition

Postby Rick Spivey » Sun May 04, 2014 6:28 am

Now it sounds like you have things in proper order. To repeat John, the terminal on the side of the magneto housing does not provide an ignition source, it grounds the points to kill the tractor engine.The oil on your magneto rotor is because someone "over-oiled" it, and it can interfere with proper spark. It only takes a couple of drops per year in the oil hole to keep a magneto running well. For clarity, you should refer to this device as a magneto in future posts, and not a distributor, since that term is usually associated with the battery ignition devices. It will just help us troubleshoot with you if we know for sure which system we are dealing with. Both devices use a distributor cap, hence the confusion.
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Re: 1948 Cub Ignition

Postby Posco » Sun May 04, 2014 7:11 am

Rick Spivey wrote:Now it sounds like you have things in proper order. To repeat John, the terminal on the side of the magneto housing does not provide an ignition source, it grounds the points to kill the tractor engine.The oil on your magneto rotor is because someone "over-oiled" it, and it can interfere with proper spark. It only takes a couple of drops per year in the oil hole to keep a magneto running well. For clarity, you should refer to this device as a magneto in future posts, and not a distributor, since that term is usually associated with the battery ignition devices. It will just help us troubleshoot with you if we know for sure which system we are dealing with. Both devices use a distributor cap, hence the confusion.


Thanks, Rick. I'm going to try and fire it up in a bit. I'm the guy who saturated it with oil, I got too exuberant with the oil can when I found the magneto so grimy. I sprayed it with Brakleen, PB Blaster and then oiled the daylights out of it from the impulse coupling end. Too much it appears.

I think I read you do fine work rebuilding them. If that is the case, I'd love to send you mine.
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Re: 1948 Cub Ignition

Postby Posco » Sun May 04, 2014 9:11 am

Houston...we have a running tractor! I was so confident I had covered all the bases that I went to the extraordinary length of putting the gas tank/hood back on. Turned on the gas, hit the starter...and nothing...but wait, a sputter? It was a sputter. A little coaxing with the choke and throttle and it came to life. It's out there running and charging the battery as I type. You guys walked me through the charging system a few months back.

I think a little tear of pride on your part for the distance you've taken me is completely in order...and won't count as a strike against your manhood.
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