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Farmall A Magneto skips time

C

ccaissie

Member
I have found twice that this magneto has slipped timing...necessitating a recheck of the timing, and moving the spark plug wires in sequence to the next position.

The little gear set under the rotor seems to be ok, and rotor sits firmly, it seems, but I'm not all that familiar with whatever can go wrong.

Any ideas?
 
The cam that opens the points is just pressed on. It may be cracked & loose. Otherwise I would guess the timing gears may be stripping over. Or somebody is playing tricks on you.
 
When it quits again bring No1 piston near the radiator to tdc on the compression stroke. Then remove the cap and see where your rotor is pointing. If it isn't pointing to the No1 plug wire your drive gear on your mag may have sheared the woodruff key or on the cam gear. Hal
 
Runs great for many hours. Farmer ran it out of gas, and wouldn't restart, even pulling it only made it burp.

I'm also tracking on a loose component like a cam or whatever that is slipping.

It seemed to be exactly one "tower" out. Lined up flywheel mark at TDC #1, and the rotor was way off. Moved the wires clockwise one position, i.e. advanced 90 degrees, and runs great.

I doubt sabotage. Will investigate how these things are actually built and look at slipping components.

Thankx
 
How many times has this happened?

For it to slip EXACTLY one position in the distributor cap is suspicious. It is practically impossible for that to happen in the real world without human intervention.

If this has only happened once, then odds are the farmer pulled the wires to troubleshoot, and put them back wrong.

Multiple times, someone is playing tricks on you.

The timing just does not slip exactly one position.
 
Are you sure the rotor isnt worn and does not lock on the shaft like its supposed to. The rest of the stuff in the mag are bullet proof and dont slip. If there are teethe gone from the cam or gov gear that would let it jump out of time. You say you move the wires and it starts that would almost make the gears on the gov and cam the culprit you can remove the gov assy then you will be able to check those gears for missing teeth. When everything is lined up #1 position on the mags rotor will be lined up at approx 1 oclock position where the base of the coil sets in line. I would pull the gov assy off to check for missing teeth on either the gov gear or the cam gear or maybe some are gone from both.
 
Link to official IH Blue Ribbon mag service manual...

http://www.cleancomputes.com/Cub/Blue%20Ribbon%20Service%20Manuals/GSS-5035%20Service%20Manual%20Magnetos/index.html
5035
 
I had the same problem a few years ago. Took me several weeks and some new words to figure out what was causing this. The mag drive gear or timing gear was moving toward the front of the tractor letting the mag lags slip out of the slot in the timing gear. The only thing that keeps the gear from moving away from the mag is a thrust spring and thrust pin. To get at them you need to remove the governor housing. You can do this without removing the radiator but it takes a little time and patients. Once that is removed you will see the shaft that is connected to timing gear. It has a thrust bearing and thrust sleeve riding on it. The shaft is hollow and it has a spring and pin in the end. That spring is either bad or needs to be stretched a little to hold that timing gear into and toward the mag. Hope this helps.
 
Great tip i had forgot about that. Ive had some to replace that spring and get all the busted,rusted old one out cand sometimes be fun. You can go to a store that has a great selection of spring to get a new one. We have a hardware store near her and they do have them same as the bumber spring in the gov.
 
But exactly one position on the distributor cap?

I can believe jumps/skips, but they would be random in nature. You'd end up with the rotor somewhere in between posts.
 
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