Magneto ?

FM J4B73 mag Ford 4 cyl L Head. Had always had my mags rebuilt by a local shop but
the guy who did it retired. He always set my mags to fire on #1. I shipped it off to
be done got it back mounted it brought #1 cyl to tdc, tractor wont start all wires
where they belong, got plugs out they fire great 1-2-4-3 but not at the right time.I
called the mag shop and asked him if he had set the mag to fire on #1 tdc, he
says dont need to on a mag you just "move the wires around" till ya get it to go.I
ask aren't the rotor and drive shaft timing marked to bring a mag to fire on #1?
Next I say why then do they have the cyl #s on the cap------he says I have no idea
why they bothered to put cyl #s on the cap. Next ? again to him was why are the
shaft and rotor marked to time the mag,he gave me a reason which I could not
understand and at that point I wished him a good day. I know how to time the drive
and rotor with #1 tdc.Being curious is why I post my ? is he in line with other mag
repairmen, and why did the manufacturers of the mag put cyl #s on the cap, I can
only come up with one answer.

WW2N,Some info for you.Follow instructions below and set your mag to number 1,and engine to just before #1 TDC.

WW2N,Some more for you.

Hey Den Im usually on the N forum and have talked to you about your boys Mustang(been a while) and other stuff I have FM Mag book dated 1951 but I will look at your reply you went to a lot of work so I wont let it go to waste. I posted a WW2 2N magneto book on the N site last week it spoke of Patriotic Farmers using steel wheels and crank start. Even the gurus over there dont get involved in mag ?s so I came here. What Im looking for someone who had a rebuild and not set right, ya dont move the wires around like this guy told me. at least not me its my trailer queen. I had this tractor forty years and the mag rebuilt by the same guy 3 times in 40 years. it was a working tractor until 2014

Magneto's are timed internally, SEPARATE from the engine. Once the magneto timing is set, you do not have to do anything to it - just bolt it on. This is NOT like a distributor. I would guess the gent you sent it to is reputable, and knows what he is doing. I work part time in a magneto/distributor/carburetor shop (doing carburetors).. But know a little about magnetos as that is all I run on my tractors. In order to install a magneto on a tractor, bring whichever cylinder you want to TDC on the compression stroke (preferably #1 cylinder)... Then ensure your rotor is pointing to whatever mag cap terminal you are going to run your wire to #1 cylinder. The numbers on the cap make NO difference (it only matters where your rotor contact is pointing to). Even if you get it wrong, you can rotate the wires either 90 forward, 90 back, or 180. (I have a habit of being 180 out on my timing - usually the more common issue)... Easy to correct, though. If you want to worry about your "#1" marking on your cap being correct with the #1 cylinder - pull the mag off, and cycle it until the rotor is pointing at the correct terminal. If you are 180 out, cycle it twice, and reinstall. The more challenging is when you are 90 degrees forward or back (although still not difficult).

At the shop, we get customers all the time who say their magneto timing is off, then they pull the magneto apart and start messing with the INTERNAL magneto timing gears.... My shop owner has even made house calls to his local customers to show them how to install a magneto because they SWEAR it is the magneto. EVERY time people seem to get so bent on what position the magneto is in. It only matters where the rotor is pointing to, and where you are running your spark plug wires. In a nutshell, whatever cylinder is on TDC of compression, run the spark plug wire from the terminal that is next to fire to that cylinder. Then, follow your firing order in the correct rotation of the magneto.

I hope this helps....

These are 75 yr old stickers C is clockwise A is for?????? Anti-Clockwise the had not discovered CC Counter Clockwise in 1943.

Also, regarding your question about rotor and drive shaft timing - they are set to give spark at a particular point in the rotation of the magneto... It has nothing to do with whether or not the engine is on TDC of #1. They are two separate systems. The magneto is timed internally to give spark at a particular drive lug angle. If the engine crankshaft, camshaft, and governor are in time, and the magneto is bolted up to that system, it (the magneto) is set to fire at the same time in the rotation, every time. Realistically, the governor/magneto drive is what causes the magneto to fire at a specific position in engine rotation. This is all getting WAY more in depth than we need to be.

Essentially, if you bolt the magneto up blindfolded, and hook up your wires, you have a 25% chance of being correct on the first shot. If not, you can simply rotate the wires around to correct the firing order.

On a 2-cylinder JD tractor, it is even easier. Just flip the two wires around and it will go!

C is for clockwise, A is for counter-clockwise rotation. I am guessing they used A instead of CC so that you wouldn't confuse a single C with a double-C..

Yes a JD will go but not correctly as one plug is not firing at the correct time. Found that out close to 50 year ago. I forget the order now as has been too long but they will start easier if wires are at correct place.

No the A stands for anti-clockwise. Otherwise there would be two C s.