getting tractor to fire after taking off the mag

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getting tractor to fire after taking off the mag

ron I took off the mag to clean it an change the points put the mag back on tractor will not fire, found the fire mark on fly wheel an put the mag back on but tractor will not run but the plugs are firing but not at the time when they are to fire need help getting it to fire on time
Butch in Ohio First thing is I need to know what mag you have. Assuming it is a Fairbanks I need to know if it has a one piece cap or two. If it is a two piece cap you probably have the rotor out of time with the points also. If you have the two piece cap repost so i can help you get the rotor in time. To time the mag to the engine if you have a one piece cap (and after you get the rotor back in time on a two piece cap) remove the cap (or outer cap, two piece) and turn the mageto backwards (couterclockwise) until the rotor is pointed to the Number 1 terminal. This is the upper terminal towards the inside, about 10 oclock looking from the rear. Remove all the spark plugs to make cranking easier and had crank until you can feel compression pushing against your thumb stuck in the #1 (front) sparkplug hole, (two people is easier), then crank until "TDC" or "center" mark shows. If you go over 1/2 turn you went by, start again with your thumb. Once engine is set at TDC the slots for the drive dogs should be at or near straight across. With the rotor on the mag pointed as instructed the drive dogs will be near straight across too. Align them by turning the mag slightly and install mag. For now put the adjustment in the middle of the slot and snug the bolts. Verify the timing by hand cranking the engine slowly until the impulse just clicks. Every other click you should see or be very near the "TDC" or "center" mark. If you hand crank the tractor it is imparitive that the mag snaps AFTER TDC, not before. Otherwise you asking for a kick from the crank. The order for the wires is as follows. Top inside terminal of Mag is #1. Top outside on mag is #2. Bottom ouside of mag is #4. Bottom inside of mag is #3.
ron in ohio Hey butch I have a two piece cap, plus I have a repair book for this tractor but it does't tell how to set up the mag timing to the engine timing
ron The mag is a fairbanks morse
Butch in Ohio Ok, since you had both caps off to clean the points I will assume that you did not know you have to time the gears upon reassembly of the first cap and that you have fire at the plugs is a matter of luck. You must retime the gears unless you were darn luckly. To check the rotor timing turn the drive in the direction it runs, clockwise watch the direction the rotor turns and when you come to the impulse catch the rotor should stop in a postion just ahead of a plug terminal and should cross it when the impulse trips as you keep turning the drive (easier done in a vise, clamp it by the bottom mounting flange, never squeeze a mag body in a vise)To time the rotor you first must realise and remember that the magneto does not fire when the rotor passes a button on the cap, it fires when the points open. if the rotor is not pointed at a button or the wrong button you never going to have spark at the right plug at the right time. There is a book way to time the rotor but this meathod works best for me. First thing you do is remove both caps, then remove the small cap and notice the position of the top inside terminal, the one for the #1 wire. You need to place a mark on the inner cap that shows where the rotor needs to be to be inline with the #1 terminal on the outer cap. Then turn the magneto backwards (so you dont have to fight the impulse coupling) Until the drive dogs are horizonal, or straight across some would say. Then turn it backwards until the points just close (remember you are turning it backwards and when going the other way they will be just opening) Hold the drive in that position and install the inner cap while timing the rotor to point at the reference mark you put on the cap. Now you will have the rotor pointing at a plug wire when the points open and you can install per my instructions in post #1
What is a mag? I also have an Allis Chalmers tractor that will not start. I bought it used and it worked fine for a short time but now it will not start. I have changed the spark plugs and it will turn over it just will not start. Two of my cylinders are burning clean and two are not. I have also put in a new battery. Do you have any suggestions?

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