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New farmall H owner... ran great for 3 days now wont start.

C

chevy_cowboy

Member
Hi guys, last week I bought a '49 H, the tractor is well used, but started and ran fine for the last several days.

Yesterday it died once on me, and wouldn't refire. I pulled the cap off the magneto and found a couple chunks of dirt dobber nest inside, cleaned that out and put it back together and it fired right up. I thought I'd solved the problem. Later that night I was showing the tractor to a friend of mine and it started ran about 90 seconds and died suddenly. Nothing we did would make it fire again.

I immediately suspected the magneto again, but testing the coil wire and a couple spark plug wires against the block they're sparking... but its a orange spark, not the bright blue I'd expect from a distributor. Is that normal for a magneto?

Any ideas on what to try from here? I'm a pretty decent mechanic but these tractors are way before my time and I've got alot to learn!


If it matters the tractor is pretty much all original except for a old 12v generator conversion that was done in the 60s according to the seller.
 

An orange colored spark is not normal. It should be blue, as you suspected.
Hopefully the mud dauber nest didn't cause any real damage, but I doubt if it did. With a magneto, you do need non-resistor spark plugs such as Autolite 3116, and also you need solid, copper core plug wires, but since it DID run pretty good, and then it didn't, it might just need a set of points and condensor, or maybe just drag a dollar bill through the contact points and clean the crud off. Worst case scenario, the mag coil is getting weak and needs to be replaced.
 
Could a bad impulse coupler cause this? I was reading this morning about magneto's and found out they're supposed to click when cranking... unless I just can't hear it I'm pretty sure mine doesn't click.
 
A good mag will throw a fat, blue spark even at cranking speed. A weak orange or yellow spark will give starting trouble as you've found. A couple quick things to check:

- Is the mag impulse coupling tripping? It should give a noticable "snap" every 1/2 revolution when cranking. If it is not snapping, the impulse needs to be cleaned, oiled and checked for a broken main spring.

- If the impulse is snapping look next at the points. Run a $ bill through them a few times to clean them up. (Use a $20 if showing off to friends...) Then reset the gap to 0.017.

If the spark is still weak be looking for failing condenser or weak coil.

Good luck!
 
C-B: You got it!

A working impulse issues a very noticable snap as each piston reaches top dead center (ie. very 1/2 crank revolution). If you're not hearing the snap you've found the problem!
 
Ok, well you guys have given me a few more things to look at, I'll go dig into it and see what I can see and report back.

If the impulse coupler is bad is it possible to replace them or would that require having the magneto rebuilt?

Thanks for the help!
 
well now I'm really perplexed. I hit the button and it fired right up. Seems to be a intermittent problem. I cleaned the points and checked the gap, all seems ok there. The shaft on the magneto has a bit of play in it, not sure how much is normal. Also found one of the screws that holds the base of the cap on was loose and tightened it.

There's definitely no clicking from the mag though.
 
(quoted from post at 14:58:02 09/13/10) Pour some gas in 'er? :>)

Allan
Click to expand...


Its funny you mention that... a few hours after I bought it at the auction, I ran the battery down trying to start it because I didn't know they'd turned the gas off under the tank :oops:

The auctioneers fired it right up before it sold, ran great.. then I hop on it to take it home and crank crank crank crank lol. Finally a old man walked by and said you turned the gas on right? :shock:
 
There isnt any place for a wasp to get into the coil on a mag unless you have a big piece busted off. That cover has four screws and a gasket to seal it to the top of the mag. Something is wrong somewhere.
 
I think he got it running with cleaned and gapped points. I agree it would be a small wasp to get in (unless someone left he cap loose because it didn't run anyway.) Jim
 
(quoted from post at 18:47:58 09/13/10) There isnt any place for a wasp to get into the coil on a mag unless you have a big piece busted off. That cover has four screws and a gasket to seal it to the top of the mag. Something is wrong somewhere.
Click to expand...

the nest was under the wire cap, not the coil. Not sure how they got in there.
 
They all missed one LMAO. This may not be it seeing as how an orange spark is bad. However, most of these old farmalls will run even if they have weak fire. They may not run well but unless you flood them they run. Any tractor I have seen, and I own one right now, that runs for a minute or so after start up then shuts off has a stuck needle in the carb. See if you have fuel in the bowl.
 
ok, now I'm really lost. Its back to not running again, didn't change anything before trying to start it again tonight and nothing.

I decided to check the timing and make sure it was right and the firing order was right... with the timing mark pointed at the 1st of the double notches on the crank pulley, the rotor is pointing straight at the floor.... which is between #1 and #3 if I'm reading my book right. And to top it off the spark plug wires aren't even close to to the layout in the I&T book.

I don't really know if this applies to tractors and magneto's or not, but if this was a small block chevy I'd suspect somebody had dropped the distributor in 1 or 2 teeth off and instead of fixing that they just rearranged the plug wires to make it run.

The shaft of the mag also has almost 1/8th a turn play in it. and there's no clicking or snapping that I can hear while cranking the engine.


Any ideas on where to go from here?
 
Magneto only works one way, if the cam gears are installed properly.

Besides, it ran before. Engines don't just jump 1-2 teeth out of time, then jump back and run fine again.

If the tractor runs 90 seconds then quits, then restarts the next morning, check the carburetor.

When it stalls, pull the drain plug out of the bottom of the carburetor. I bet nothing runs out.

You have a carburetor problem.
 
(quoted from post at 00:59:09 09/14/10) ok, now I'm really lost. Its back to not running again, didn't change anything before trying to start it again tonight and nothing.

I decided to check the timing and make sure it was right and the firing order was right... with the timing mark pointed at the 1st of the double notches on the crank pulley, the rotor is pointing straight at the floor.... which is between #1 and #3 if I'm reading my book right. And to top it off the spark plug wires aren't even close to to the layout in the I&T book.

I don't really know if this applies to tractors and magneto's or not, but if this was a small block chevy I'd suspect somebody had dropped the distributor in 1 or 2 teeth off and instead of fixing that they just rearranged the plug wires to make it run.

The shaft of the mag also has almost 1/8th a turn play in it. and there's no clicking or snapping that I can hear while cranking the engine.


Any ideas on where to go from here?
Click to expand...

The magneto kill switch, or the ground wire may be suspect. Disconnect the grounding wire from the mag and see what happens.
 
The carb isn't in the best of shape, but its getting gas to the plugs. Also in the way it dies, it doesnt sputter like its running out of gas, it just shuts off like you killed it with the switch. I'd almost wish the problem was the carb, I feel way more knowledgeable about carbs than magneto's at this point.


I unhooked the ground wire to eliminate the switch yesterday and didn't change anything.
 
(quoted from post at 05:30:36 09/14/10) The carb isn't in the best of shape, but its getting gas to the plugs. Also in the way it dies, it doesnt sputter like its running out of gas, it just shuts off like you killed it with the switch. I'd almost wish the problem was the carb, I feel way more knowledgeable about carbs than magneto's at this point.


I unhooked the ground wire to eliminate the switch yesterday and didn't change anything.
Click to expand...

Have you removed the coil cover and had a look? The cover has a contact point that rests on top of the coil. Might be a corrosion issue?
 
The mag must snap when turned slowly. If it does not, the impulse coupling is either gummed up, or broken internally. Without the impulse coupling, the mag will not make enough spark at cranking speeds to start the tractor.
If it has run, don't change the wires or timing, the issue is in the impulse coupling. Jim
 
Ok, I ordered several reproduction service manuals the other day, including one for the magneto, so hopefully they'll be in soon and I can find the impulse coupling and check it out. I don't really want to dig too deep into it without a decent manual.
 
well I'm still waiting on the manuals I ordered, but after talking to a old timer at the local CNH dealer who seems to know alot about magneto's I ordered a rebuilt mag. He seemed to think I've got too much freeplay, and as we suspected a bad impulse coupler.

I still think someone did a bad job of timing it too, but thats easily solved when I put the rebuilt on.
 
I got the newly rebuilt magneto today and got to work on swapping them.

The distributor drive was 1 tooth off timing, that probably didn't help any, and the impulse coupling on the old mag is all gummed up.

Retimed the drive, and popped the rebuilt mag in the hole along with some new plugs and wires and she fired right up, runs smooth and so far seems to start everytime instead of just when she feels like it lol.


Thanks for the help guys.


Now on to rebuilding the steering box and bolster so 5th gear is actually usable without scary shimmys :lol:
 
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