Need Some Help... Bad...

Bryce Frazier · Oct 11, 2015

We have been trying to get my Farmall M running, again, and we just for the life of us, can't make the thing run! I am sick and tired of fighting with it, tried to sell it yesterday...

Anyways, here is where we are at. The mag is PERFECTLY timed with the 1st notch on the pulley on the engine, just like the book says to do. WHEN the mag snaps, it produces a LARGE BRIGHT BLUE spark at the coil wire, however, the spark plugs rarely fire, and when they do, the spark is pathetic. We have tried 3 different sets of wires, 2 caps, 2 rotors, a different carb, re timed everything 10 or 12 times, and it is the same story every time.

We finally realized this spark issue with this mag, we have another we could try, but I suspect things are the same...

Anyone have any help??? Where do I go from here????

Andy Martin · Oct 11, 2015

You didn't mention new spark plugs. Can you drag it and get it started? I can't remember all your issues. Seems like you put a new carburetor on it, but I thought it was running, just not running well. Have you confirmed the timing mark and TDC match up? Have you confirmed compression? Valves sticking just a little can sure keep on from starting. You're sure you have a gasoline magneto? Have you watched it turn with the cap off? Does the rotor bug line up with the post in the cap when the magneto snaps?

JF in MI · Oct 11, 2015

Don't know much about tractor magnetos but if they are similar to aircraft (and I'm betting they are) there may be gearing inside. If there is and the gearing is not "aligned" (usually some kind of mark) the coil can fire when the rotor is nowhere near the proper post on the cap. Your spark has nowhere to go.

todd hamilton · Oct 11, 2015

Tried a different condesor? You're describing classic bad condenser symptoms. Breaking down with repeated impulses

fixerupper · Oct 11, 2015

JF I ran into that problem with a Farmall B, which could be the same mag Bryce has. It always started OK but one day it just wouldn't start. I finally discovered the rotor gear, or that's what I will call it was one tooth off so the spark had to jump too far from the rotor to the post in the cap. It had been running this way for quite awhile but for some reason, dirty points or whatever, the spark got a little weaker and wouldn't jump that gap anymore. I advanced it one tooth and it took off like a champ.

Bryce, I have a hunch at might be the problem. it's worth checking it out.

T.R.K. · Oct 11, 2015

I had a MM on a magneto once that the little shaft the rotor was on froze in its bushing and stripped the hub in the fiber gear that ran off the main shaft in the magento. It was a Fairbanks Morse magneto, though.
It would fire every once in a while when the spark and valves were close enough.

If I was you, I would try the other magneto.

You aren't trying to make it run with carbon plug wires, are you?

If you have tried timing it so many times, there is no possible way you could be 180 degrees off, trying to fire whichever cylinder is opposite #1 could you? Remember, the gear reduction inside the mag reverses the direction the rotor turns. (At least for most 4 cycle magnetos)

You could also try to find a distribuitor for that engine, as I think it would fit right on where the magneto goes.

gene bender · Oct 11, 2015

Yes that is very important to have the rotor lined with the tower when it fires .

gene bender · Oct 11, 2015

I would remove all plugs hook up the wires make sure they are in firing order. Then put your finger over the hole and when engine is turned with starter you can see the fire when compression is reached that way you know the mags rotor is timed correct. I have several mags on Farmalls and thats the way i check to make sure everything is in order.

UncleTom · Oct 11, 2015

The spark plugs cannot be black sooty type color. Must be white or brown in color. Black in color is fouled.

pete 23 · Oct 11, 2015

you say timing but not which timing. Impulse to engine or internal timing of rotor to cap. I would guess your rotor timing is wrong. Under cover with two screws. Marked for left and right rotation and that means from turning the mag impulse so M is right. It takes patience and perseverance to work on these old girls. Figuring out what actually makes them tick and a no start problem can be a hundred different things.

Bryce Frazier · Oct 11, 2015

We have thoroughly, and repeatedly checked BOTH of those. BOTH are set right were they need to be, and everything is happening when / where it should.

Bryce Frazier · Oct 11, 2015

Thats what dad was thinking, we will give that a try next I think... Thanks...

Bryce Frazier · Oct 11, 2015

Haven't put new plugs in it, but these are really good ones for sure. Never have drug it yet... Might try it though?

We completely rebuilt the carb, and that doesn't seem to be the problem, because WHEN it was running on that Prestolite mag, it was running well, but once that one bit the dust, everything went to he!! in a handbasket!

Timing marks / tdc / all that are on the money.
Haven't tried compression, but by feel, it is pretty good.
Valves might need adjusting, but we will know that more once we get it running though.

Bryce Frazier · Oct 11, 2015

This one was completely off when we got it. I THINK someone was running the plug wires backwards or something... Either way, we have it set so that ONCE the mag "snaps" it is DEAD on the point it should be on in the rotor cap...

Andy Martin · Oct 11, 2015

While I understand your frustration, there are only a few reasons why a mag will fire out of the coil and not out to the spark plugs. Any chance your rotor bug is mismatched and not making contact with the center tower? How do you check the spark? You say you have a good blue spark from the mag but not across a spark plug. Are you going directly from the cap to a wire held close to a ground or are you always checking through a plug? I've had plugs go bad, I think just from moisture. Are you using solid copper wire? I've had good luck with carbon fiber wires on Farmalls but when you are really stymied get some real wire. Also, you know that diesels rotate in reverse to a gasoline magneto, otherwise they look identical. Is the rotor bug rotating CW as you crank the engine?

notjustair · Oct 11, 2015

Put new spark plugs in it. I have seen spark plugs that were run over rich or flooded do exactly that. Put in new ones and it fired right up.

Janicholson · Oct 11, 2015

The rotor timing can be a pain. If you pull start it, and it runs well, I will agree the rotor is timed If not check it again, the rotor seems to be off just before it trips when it is good to go. Jim

JF in MI · Oct 11, 2015

Some of these answers have me a little interested and I'm hoping I can learn something new here. What does/would a diesel use
a magneto for? First time I heard of it.

oldsarge · Oct 11, 2015

Early IH diesels wers true "dual fuel" Start 'em on gas with regular ignition,get 'em warmed and turning,and switch to diesel.Look at the engine,on one side was gas and the other side diesel.

Tom OConnor · Oct 11, 2015

JF,
The older International Diesel's had a mag or battery ignition on the right side of the engine and spark plugs and started on Gasoline till they were warmed up a little and then you would switch them to Diesel.

John - OH · Oct 11, 2015

Try some new plugs.

OldBuzzard · Oct 11, 2015

I'm with the guys that say try new plugs, and use an inline spark tester as opposed to just removing one, grounding it and seeing if you see the spark.

Plugs will often pass that test but fail to fire when they are under compression.

CenTex Farmall · Oct 11, 2015

Does the Mag snap cleanly every single time?
Had trouble with an H earlier this year. The impulse coupling was weak. It would fire and make a spark but I figured out it wasn't snapping cleanly every time. Tried a different Mag and was up and running.

JF in MI · Oct 11, 2015

Never knew or even heard of that. Sounds really neat but complicated. Must have solved a lot of cold start problems assuming it worked as it should have.

Bryce Frazier · Oct 11, 2015

Just so you guys know, when we have been testing for spark, we have NOT been using the plugs. One of us holds the spark plug WIRE about 1/4 inch from the engine block (ground) and turns the engine over. There will rarely be a spark, and when there is, it is orange (weak)

HOWEVER when you do this EXACT same test, but use the middle wire (so the spark is now coming directly from the condenser) it jumps a STRONG (1/2 inch strong) bright blue spark???

So, the problem is that this nice spark, dissapears when it is sent into the rotor, and then distributed properly.

Bryce

Janicholson · Oct 11, 2015

Put a distributor on it from one of the other ih tractors around the place. It will run then. Jim

JD Seller · Oct 11, 2015

Bryce It sounds like your trouble is in the rotor itself or the cap on the mag. You state you have tried some others and are getting the same results. So either your mag is bad or your timing the mag/rotors incorrectly each time your replacing the rotor. Since you have good fire out the coil when it fires, but not out the plug wires, I think your not getting the rotor timed correctly. Forget looking at the books/manuals on timing the rotor. Bring the tractor up to little before TDC on #1 cylinder. Set your mag timing to just be ready to fire. Then set the rotor to be lined up when it does fire. I will bet your Dad knows how to dead time a car/truck motor. Do the same thing to this one. FORGET using the marks and such on the mag. You do not knew if everything up stream is installed right so just dead time it to see if it will run. Then you know that some one has some thing timed wrong up stream.

Truthfully your trouble is why I usually convert these old tractors over to a distributor and coil like more modern tractors. Put the mag on a shelf for a collector item. There are several kits and many used ones available for a IH "M". They will start better and the on going maintenance will be much less.

Goose · Oct 11, 2015

This might be a little too basic, but I assume the mag is not 180 degrees out?

That being said, I think NEW spark plugs would be worth a shot. They're cheap. With two H's and an M, I always keep an extra set of new ones on hand.

Bill(Wis) · Oct 11, 2015

Try Todd's suggestion, new condenser.

CenTex Farmall · Oct 11, 2015

As Andy Martin mentioned were the wires the solid core type or suppression type?

The H I mentioned earlier is just a run of the mill, worn, '43. Not a lot of compression but it starts with a good 1/2 turn of the crank (after a slow turn with choke to prime).

huntingreen2day2 · Oct 12, 2015

So it ran with another mag but will not run with this one. Did you use the same distributor cap that was on the Prestolite mag? My guess is there is a mismatch between the cap and the magneto.

Roger in Wisconsin · Oct 12, 2015

I may be wrong, but I think the snap comes after TDC. It's a retarded function built into the magneto for starting. At higher RPMs it is advanced.

Bryce Frazier · Oct 12, 2015

I've tried both, doesn't seem to make a difference. Solid core is what I usually run though.

Bryce Frazier · Oct 12, 2015

Nope, I have the prestolite mag, and 3 IH mags, I have made very sure to ONLY interchange parts that are, well, interchangeable!

JMOR · Oct 12, 2015

(quoted from post at 09:48:37 10/12/15) Nope, I have the prestolite mag, and 3 IH mags, I have made very sure to ONLY interchange parts that are, well, interchangeable!

ften, mags can be set up to operate for CW or CCW rotation.........are we sure that this aspect is correct here??

teddy52food · Oct 12, 2015

Please tell us how you timed the rotor gears. What marks did you use?

Brad Gyde · Oct 12, 2015

I'm gonna jump on with rotor timing being off.. I'm going through the same issues with a newly acquired T6 crawler (m engine, h4 mag). There are 2 marks on the rotor.. One marked L and one marked R (for clockwise/counterclockwise rotation) my rotor drive is/was on the wrong mark. Also, I didn't know that points should be set to .013, not the .020 like I always set them in distributors.

From your description of your timing process, you're using an I&T manual... Throw that in the garbage and get an IH manual.... Way more details on mag repair. I have a I&T, the IH came with the crawler I got.

Don't give up.. No fun in that!

Good luck
Brad

jimg.allentown · Oct 12, 2015

If the spark is "disappearing" as you say, then there is a problem with either the cap, rotor, or wires. Something is drawing down the spark.
The rotor can have a pinhole in it that can short the spark to ground. Sometimes, the offending hole or carbon track can be impossible to see. If you have a spare rotor, try that and see if anything changes.
The cap can have carbon tracks in it or on it either inside or out. Outside ones show up in the dark, inside ones are harder to see. Again, if you have a spare cap, it may help.
Wires: Check the resistance of the wires. Something in the neighborhood of 6000 to 10000 ohms is good for a resistance wire, and near zero for solid wires.

In ANY case, your spark is either being drained off by a short/partial short or not getting through because of high resistance. Without good spark, fuel, timing, and compression are irrelevant.

tractorguy2 · Oct 12, 2015

I really doubt the condenser is the problem.when condensers go bad. You will a lot of spark at the points when they open. You will have very bad if any spark at the coil.

Your solid core wires. Are they copper core? Magnetos should be used with copper core wires.

If you truly have good blue spark out of the coil but not through the distributor cap. My first guess would be the two small rotor drive gears are not timed correctly.

The large rotor gear has two marks. A letter 'R' and a letter 'L'. You need the tooth on the small gear with the bevel tooth lined up with the letter 'R' mark.

My next guess is the coil. A weak coil will have enough energy to jump a fair gap from coil to ground. A weak coil will not have enough energy stored up to make hot spark going through the rotor,then the cap,then through the plug wire,then through then the plug, and finally to ground.

Dune Country · Oct 12, 2015

"You're sure you have a gasoline magneto?" a what?
nevermind

todd hamilton · Oct 12, 2015

Can't accurately check it that way, gap and ground are everything in regards to heat and length of spark. You gotta put a solid ground on the spark plug thread, hook the spark plug wire to the plug and watch spark across the plug gap. Do it with the #1 cylinder and while watching the plug see if it sparks just before tdc. Stick your thumb over (not into) the spark plug hole while some cranks the motor. You will feel the intake, compression and exhaust. Also I agree with jd seller put a distributor on it. My dads old sc case and his 75 horse Johnson outboard had mags when I learned from him. What I learned is they are touchy pains in the uh "neck"

Need Some Help... Bad...

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