h4 magneto 180 off

calcubman

Member
i think my mag / timing is off 180, as i hand crank the engine starting from #1 TDC the mag snaps after about half a crank, then the #3 is at TDC and then mag snaps after about 1/2 down the cylinder, (i am guessing..
does this mean timing is off 180 degree. ?
 
Where is the rotor when @1 is on TDC and do you have the wires in the cap in their proper places #1 is around the 1 oclock position then #3 then #4 then #2
 
the rotor is just before #1 (1 oclock position. when i crank it the mag snaps after the compression stroke is half way down the cylinder.
on another note i did reverse the rotation on the mad from CCW to CW, and i did everything correctly as mag manual states. the mag snaps in the same position on every cylinder just after the down compression or other words the power stroke .. the rotor is at the correct position every time, it just snaps late .
 
I think you have it timed late, not 180 off. The mag should snap at TDC. Then when running it goes to full advance as the impulse coupling governor gets up to idle speed. Were it mine I would rotate the mag so it snaps at TDC. Jim
 
I wish I was looking at it. If the mag can be rotated on its mount in the correct CCW in the slot on the bottom bolt, do that. If it cannot be adjusted there, (and if it has never run after major engine work) the timing gears in front of the governor might be off one tooth. Jim
 
you changed the mag from a LH diesel to a RH gas? If you did you have to retime the rotor drive gears and change the impulse drive to a RH.
 
You may need a different drive cup with the lugs in a different position. Easier to change the gear timing. It should snap at TDC, not part way down.
 
You have to change shafts for right hand drive keyway is in different positions for Impulse coupler on right and left drive BTDT.Ralph
 
the problem was ,, i had a magneto from a TD6 ,gas start diesel, then i changed the rotation from CCw to CW,i did everything the book said and fellow forum members said, what turned out to be was the degree is different from the CCW diesel to the CW gas. it wont work.. i tried it
 
I looked up the armature and they show a differnt part number for diesel than they do for gas so I assume the keyway is cut in a different position.
 
OK, I have been watching this thread, and there have been some suggestions. The only way to be 180 degrees off (if the internal timing is correct) is if you have the drive lugs 180 degrees out when you mount the mag on the tractor. Also, has the governor gear been out/moved? what is the history on the engine. rebuilt? did you change the impulse over? there are CW and CCW impulse assemblies, and they MUST match the rotation.

The best way to correct your issue (if everything else is right) is to change the mesh point on the rotor drive gear inside the mag. There are two markings on it (R and L), one for CW rotation and one for CCW rotation, as it is the same part for both mags. the timing mark should be set to L for CCW (diesel) and R or CW or gas. Since I cannot see and did not see what you actually did, it is hard to guess at exactly what is wrong.

if you have the gear timed to R, and are still having issues, open the front of the mag up (can be done while still on the tractor), and pull the points cover off. While noting the rotation of the drive gear for the rotor, advance its mesh by 1-2 teeth, and test again. When you get the impulse to trip at TDC, you SHOULD be ready to go (not knowing what all has been done).

Personally, I would have sold the diesel mag to someone who needs it and get my money back to invest in the correct mag, or I would have transferred the new parts(coil, points, condenser, etc) to a donor mag body. When you are done with this adventure, you will have more $$$ invested in your labor that you paid for the mag. When you are done, you will have a modified mag, custom timed internally, where the rotation and the timing do NOT match the serial number. While you own it, not a crisis. If you sell the tractor, it will be someone's nightmare down the road. It is your tractor though, and I do wish you good luck.
 
I can see what's wrong. And changing the rotor gear
is not going to change where the impulse trips. And
I am not sure changing the gear position on the
drive will help as the armature may be in the wrong
place in relation to the fields to produce spark at
the right time. It needs an armature with the keyway
in the right place. I believe mr cubman changed all
the other lefthand parts.
 
yes the keyway is at a different degree, i found a h4 mag from a super c and took it apart and set it side by side, and the degree is different. i use d it instead, put it on the B and she fired first crank runs like a charm.. thanks for all the input guys, i learned alot.
 
By changing the rotor timing, it won"t change when the impulse snaps. But it will make the spark jump a large gap because the rotor won"t line up with a contact in the cap. Time it on the clockwise mark & leave it. He needs a different drive cup or change the governor gear mesh. I have run into this before.
 
I think the best advice you were given in this thread was what Tom Fleming said:
(quoted from post at 07:08:31 09/14/14) Personally, I would have sold the diesel mag to someone who needs it and get my money back to invest in the correct mag, or I would have transferred the new parts(coil, points, condenser, etc) to a donor mag body.

But that ship has now sailed. It looks like you have now used up 2 magnetos to make one that functions one way or another and have a left over pile of mostly useless rubble.
 

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