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Magneto timing, rotor position vs. tower

Hendrik

Hendrik

Member
Farmall Super A H4 magneto.
While rotating the engine with the hand crank, the rotor of the magneto rotates approx. 45 deg. at half the rotational speed of the crank and then stops. The crank then rotates through another 90 deg. and the impulse trips and the rotor jumps through the "remaining" 45 deg.
I know this is how the impulse is supposed to work.
Now my question: should the rotor point to the corresponding (TDC compression cylinder) tower on the distributor cap BEFORE it jumps
or should it point to that tower AFTER it has jumped?
 
just before. the mid point of the impulse rotation should be exactly at the #1 post of the cap. The manual indicates that when installed correctly, if you rotate the magneto towards the engine when timed correctly, it should trip the impulse. Also, if you have the crank, cam, and govenor gears correctly timed, you only have 2 options with a H4 mag. In time or 180 degrees out of time. There are no other options. An F4 or E4A mag is a whole different story..........

hope that makes sense.
 
It should line very near after it impulse coupler trips. That is where it will be once the engine is running fast enough for the coupler not to engage. You can easily check the position by turning the engine backwards until you get to the timing advance running timing mark.
 
Set the internal gears of the magneto so the timing marks are properly aligned, set the igniton timing and the rotor will take care of itself.
 
I have a Farmall Super A that wont start.

I have a spark from the magneto, and I have set the magneto to fire on cylinder #1 aligned with the distributor.

I have gas, I have even used starting fluid and occasionally I get a pop from one of the cylinders.

This is very frustrating.

Philip, Tucson AZ
 
Rotor stops before the tower. It lines up when the points break open. Points open as, during , while, the impulse trips. Time the gears at the C (clockwise) mark.
 
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