1948 Cub Ignition

Tue Apr 29, 2014 6:56 pm

My 1948 Cub originally had a IHC magneto that at some point failed. The previous owner had converted the ignition system to battery and coil using the existing breaker points and condenser in the magneto. I am about to do a tune up and found that the ignition rotor is gear driven by a small pinion gear. I have removed the Bakelite cover and rotor but I do not know how to access the existing points and condenser. I removed the three screws from the cover but it does not want to come off. Any help would be greatly appreciated. In addition could this whole assembly be replaced with the IHC breaker point system? And what would be needed? Regards, Jim

Re: 1948 Cub Ignition

Tue Apr 29, 2014 10:50 pm

you are trying in the right place. Once the 3 screws are removed the cover comes off and the points are behind it. if it has not been removed in a long time it will probably be stuck and need a little persuasion.

Re: 1948 Cub Ignition

Wed Apr 30, 2014 12:18 am

Get between the cover and the body with a small flat head screw driver. Pry it up a little. Had to do that with my H4 mag.

Re: 1948 Cub Ignition

Wed Apr 30, 2014 4:47 am

You have a couple of choices. I would either replace the mag coil, assuming they left the mounting bar for it behind. Or I would replace the magneto with a complete battery ignition distributor. There are pros and cons to both alternatives, and it probably comes down to whether your magneto is complete or not. Those mounting bars are scarce, usually requires robbing one from another donor magneto.

Re: 1948 Cub Ignition

Wed Apr 30, 2014 5:37 am

When pulling the cover to access the points & condenser, you must first pull the little rotor pinion gear off. It usually slips right off, but will sometimes be a bit stuck, a small pry, behind the gear, will get it off. The cover will then come off easily.

I agree with Rick on the conversion. Remove the two screws from the mag top cover and see if the square bar for the coil is still in there.

Re: 1948 Cub Ignition

Wed Apr 30, 2014 8:55 am

Answered a question I just asked in another thread. Great.

Re: 1948 Cub Ignition

Wed Apr 30, 2014 9:08 am

Unless I have a reason to remove the Bakelite cover I normally leave it in place to remove the metal cover. Rotor stays timed that way. LOL

Re: 1948 Cub Ignition

Wed Apr 30, 2014 9:11 am

John *.?-!.* cub owner wrote:Unless I have a reason to remove the Bakelite cover I normally leave it in place to remove the metal cover. Rotor stays timed that way. LOL


Too late. How do I time the rotor? And how do I set the point gap, if you would.

Re: 1948 Cub Ignition

Wed Apr 30, 2014 9:17 am

point gap, set the magneto cam so it is holding points open to widest, and use a feeler gauge to set to .013. Turn it and check it again after setting it.

To time the rotor, go here
viewtopic.php?f=140&t=83108

Re: 1948 Cub Ignition

Wed Apr 30, 2014 9:21 am

John *.?-!.* cub owner wrote:point gap, set the magneto cam so it is holding points open to widest, and use a feeler gauge to set to .013. Turn it and check it again after setting it.

To time the rotor, go here
viewtopic.php?f=140&t=83108


Without me making any adjustment it is already over 0.020. Haven't touched the screw.

Re: 1948 Cub Ignition

Wed Apr 30, 2014 9:24 am

0.022 slides comfortably through. I had a no spark situation after I static timed my governor so I started digging.

Re: 1948 Cub Ignition

Wed Apr 30, 2014 9:38 am

I set it to 0.013 and I'm going to go put it back on the tractor. New condenser

Re: 1948 Cub Ignition

Wed Apr 30, 2014 10:04 am

Question, John. I found the timing marks on my idler gear for the governor but I'm not completely sure I have the timing mark on the governor gear itself. My question is this. With the number one cylinder at TDC, there are only two possibilities for the distributor drive lugs to be at ten and two. Is this correct? And if so, does the governor 'care'?

I think I may have a bad coil. I pulled the coil wire from the distributor and tried to get it to arch but I got no spark whatsoever.

Re: 1948 Cub Ignition

Wed Apr 30, 2014 2:28 pm

Anytime the engine is at TDC, the drive slots will be as pictured. the only thing that cares about the position is the magneto. If the points are clean, not burned or dirty, the condenser is good, and you can hear the impulse tripping when you hand crank, the next most likely cause of no spark from the coil is the coil itself, unless there is a short in the wiring or insulator where the kill switch enters the magneto. Try disconnecting the wire on the side of the magneto then if that doesn't help, look at the terminals inside. If one of them is grounded there will be NO spark. Mag coils are expensive, around $65 each the last I knew.

Re: 1948 Cub Ignition

Sat May 03, 2014 10:20 am

Update for those willing to offer help. I internally disconnected the lead wire of the magneto coil and wired up an external coil. Positive to ignition switch and negative to distributor. Still no spark. I took my meter and set it to audible tone and placed the leads on contacts (copper/brass on top of switch inside hood) of the single wire ignition switch. With the switch in the 'off' position I get tone, with the knob in the 'run' position I get nothing.

I'm going to pull and clean up the terminal on the distributor next. Running out of ideas. The impulse coupling trips, new condenser and points, timed to TDC on #1 cylinder, rotor timed with pinion gear.