mag on a Cub

Charlie M · May 27, 2015

I just overhauled the engine on my Cub and now I've run into a problem reattaching the mag. The engine had the crank shaft out, the idler gear off and the governors off.I was pretty sure I have all the dots lined up on the teeth but the mag seems to be about a "tooth late" on timing when I try to put it on and get it timed.The number one piston is down the cylinder about an inch before it fires.Only answer to me seems there is a tooth off on timing on one of the gears. Anything I'm missing?

Oldiron29 · May 27, 2015

Charlie, Can't say if your timing gears are off. But you can move the gear in the mag to make up for it to fire on TDC #1 That should get you running.

teddy52food · May 27, 2015

???????????????????????????????????????????????????????those GEARS JUST TIME THE ROTOR. It won't change the impulse timing.

Bhunt · May 27, 2015

(quoted from post at 01:16:06 05/28/15) I just overhauled the engine on my Cub and now I've run into a problem reattaching the mag. The engine had the crank shaft out, the idler gear off and the governors off.I was pretty sure I have all the dots lined up on the teeth but the mag seems to be about a "tooth late" on timing when I try to put it on and get it timed.The number one piston is down the cylinder about an inch before it fires.Only answer to me seems there is a tooth off on timing on one of the gears. Anything I'm missing?

I don't know if this will help or even if its correct I found it in the archives and thought it might apply to your problem. It was for a 1949 cub
Byron Good luck

(The Cub is unusual in that it's the *governor* that has to be timed
correctly. This is because the governor gear acts like an extra idler gear in
the mag drive train. There is a timing mark on the *rear* face of the governor
gear and the idler gear that must be aligned. You may have to remove the mag
drive seal in order to see it. It has to be right in order for the mag drive
slot to be in the right place.)
George Willer 2005

Charlie M · May 28, 2015

That was my first thought but I think since the mag fires too late I can move it so the impulse is firing the next cylinder and them back up the gears to fire the previous cylinder.

Jim Becker · May 28, 2015

Turn the engine to TDC. With the magneto removed, the drive slot in the governor gear assembly should be at 35 degrees away from horizontal oriented at about the 2 o'clock - 8 o'clock position. If it isn't, you need to pull the governor and remesh the gears so it is in that position. You can do that without seeing the timing marks.

Don't mess up the timing of the rotor inside the magneto. The mark on the rotor needs to align with the marked tooth of the pinion gear. Otherwise, when the magneto fires, the rotor will be somewhere between two of the towers in the cap.

BruceS · May 29, 2015

I had a perfect running H with a mag; firing on top dead center. Then the mag abruptly produced no spark. R and R coil, condenser, points, and distributor cap. Now has spark, but cannot get it to trip on top dead center. BTW, the h's have two timing marks on front pulley. As far as I can tell and also book says that first mark is tdc. The closest I can get it is between the first and second marks. Tractor will run, but doesn't have power it previously had. FWIW, I'm abandoning the mag and switching to a distributor.

mag on a Cub

Charlie M

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Oldiron29

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teddy52food

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Bhunt

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Charlie M

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Jim Becker

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BruceS

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