51 M runaway engine

[used red MN]

Is this what you are talking about?

Nope, the diode is shown in the circuit to the “1” spade terminal of the alternator as shown in the linked generic 12 volt conversion wiring diagram. A warning lamp or resistor can also be placed there. Its purpose is to not allow enough current to backfeed from the alternator’s excite circuit to fire the coil and keep the engine from continuing to run when the switch is turned off. When a lamp is used when you turn the switch off the light starts glowing until the engine stops due to the bulb has a higher resistance than the ignition coil. Hope you can understand that. The resistor in your picture is shown in the diagram in green, it has nothing to do with the charging system it drops the voltage to the coil.
Generic 6 to 12v alt. wiring diagram
Edit to add: The question still remains is there an alternator on your tractor or a 12 volt generator? Photo?

 

[D Slater]

Looks like a IH throttle tube and shaft or just shaft is awful close. Maybe just needs the M&W lever added to front of shaft and shaft made shorter. Looks like other changes I mentioned was for slightly different tubes between H and SH through 350. H tube is longer. Some use a H tube with a bigger carburetor added though. If you get a tube with number ending in DB they have a little seal inside next to bushing. If bushing not worn, they give a little Beter idle sometimes. M&W and IH used ones with no seal and just bushing for a lot. On the resister follow wire that doesn't go to coil to alternator and see if spliced in or goes back to ignition switch without a branch off.

 

[RedMVa]

Like others have said, you have a backfeed or a wiring problem on the shutdown problem. I don’t see why the M&W shaft can’t be repaired or you can also rework an IH governor to be just as responsive as the M&W

 

[Jim Becker]

You can also use a resistor in place of the diode, as well as an indicator light, essentially using the filament of the bulb as a resistor. I wonder if it has a resistor which is borderline to low to the required resistance. Then when it is shut off the alternator excite circuit feeds through the resistor providing a low voltage to the coil so it produces a weak spark but just enough to fire the plugs. If it has an indicator lamp the same could be true if the bulb was switched to one with lower resistance. I would need to do more research on the proper ohm value of a resistor for this application. One of the conversion diagrams I have calls out a rating of the indicator bulb as 200ma.

IH used a 25 ohm resistor.

 

[mailman1]

I am going to try and modify a IHC shaft to work in the M&W tube as the M&W shaft is complete trash, I'm surprised the shaft didn't break instead of the end giving out. As far as the ignition I was having a hard time trying to start it and then I found out the coil was bad. It had a 6 volt coil on it when I converted it to 12 volt starting and everything worked fine, when I replaced the coil the Case IH parts man said the 12 volt would work fine but after putting it on is when I started to have problems with it not wanting to shut off. Could it be possible that the wires to the coil could be reversed to cause it to not shut off?

 

[JDIH]

Gas engines will sometimes fail to shut off when you're working them hard and in a runaway situation like the OP has stated. Develops enough heat in the cylinders to keep lighting the fuel. You said it wouldn't shut off in the past, was it under similar circumstances?

 

[rustred]

A run away is when the rpm keeps increasing till the engine flys apart. Diesels are know for that. When they sniff gas in the air.or a faulty pump. The only way to shut them down is to block off the air intake. In A gas engine working hard it’s called run on. The way to cure this is to have the idle set as slow as the engine will run. Even completely closing the throttle plate. No air entering it cannot keep running. This talk of a run away engine here is confusing. I am sure it’s not running away. As said you have a back feed from the alt. Why not disconnect it to prove the point.

 

[m16ty]

Had it happen when the governor weights in my H let loose. Got a rebuild kit. Good to go!

Mike

That’s not what I’d call a runaway. What I call a runaway is when the engine goes to max rpm without a means to shut it down. Pretty common with diesels, but on gas engines all you have to do is hit the kill switch.

When a diesel runs away only way to shut it down is to somehow cut the air off to it.

 

[Absent Minded Farmer]

That’s not what I’d call a runaway. What I call a runaway is when the engine goes to max rpm without a means to shut it down. Pretty common with diesels, but on gas engines all you have to do is hit the kill switch.

When a diesel runs away only way to shut it down is to somehow cut the air off to it.

Ah, got it. I recall a vertical Fairbanks diesel that took off like that. They got the intake capped pretty quick, but it took about 20 minutes for it to come to a stop due to an over abundance of heat. They wanted to run it for someone without water going through it. Got pretty hairy for a minute.

Mike

 

[used red MN]

As far as the ignition I was having a hard time trying to start it and then I found out the coil was bad. It had a 6 volt coil on it when I converted it to 12 volt starting and everything worked fine, when I replaced the coil the Case IH parts man said the 12 volt would work fine but after putting it on is when I started to have problems with it not wanting to shut off. Could it be possible that the wires to the coil could be reversed to cause it to not shut off?

Still no answer as to you having a generator or an alternator. Does it have a charging system warning light added to it? I realize you are addressing two problems here, giving you some slack due to that. If it has a generator we needed to look at different aspects. What I said about a utilizing a resistor in the alternator circuit and the difference between the resistance (amps it requires) of the 6 volt, it makes some sense about changing to a 12 volt coil would be a possible cause if your “no shut off syndrome. In actuality if the picture you posted is of your coil to utilize a resistor as you show means you have a 6 volt coil. Seems like this may be Greek to you, but running through that resistor in your picture and having a 12 volt coil would cause the opposite. Meaning in terms of it being likely to keep running. Do you have an ohm meter to measure the coil primary side between the two small terminals with nothing else hooked to them? A 12 volt coil will read 2.5 to 4 ohms, many are 3 ohm. The 6 volt coil will be in the 1.5 neighborhood.
Remember tell us alt or Gen, if alt post a photo of it.

 

[BarnyardEngineering]

Gas engines will sometimes fail to shut off when you're working them hard and in a runaway situation like the OP has stated. Develops enough heat in the cylinders to keep lighting the fuel. You said it wouldn't shut off in the past, was it under similar circumstances?

That's "dieseling" which is generally caused by a red-hot bit of carbon in one cylinder igniting the fuel. It would truly be strange for ALL FOUR cylinders to be in that condition, and for the tractor to run smoothly, let alone run away. They normally pop and sputter along for a few seconds, eventually backfiring and stopping.

 

[BarnyardEngineering]

A run away is when the rpm keeps increasing till the engine flys apart. Diesels are know for that. When they sniff gas in the air.or a faulty pump. The only way to shut them down is to block off the air intake. In A gas engine working hard it’s called run on. The way to cure this is to have the idle set as slow as the engine will run. Even completely closing the throttle plate. No air entering it cannot keep running. This talk of a run away engine here is confusing. I am sure it’s not running away. As said you have a back feed from the alt. Why not disconnect it to prove the point.

In this case, the connection between the governor and the carburetor is broken, and there is no way to close the throttle plate.

 

[mailman1]

Well we are back online again, I went to the local salvage yard and got a good used M governor put it on and it runs like a new tractor. I had to replace the throttle plate screw as it was only half a screw and also now when I hit the ignition switch it shuts off. Could be when the linkage was messed up it would not let it die. Good thing is I got the sweet corn in now just need rain.

 

[used red MN]

Well we are back online again, I went to the local salvage yard and got a good used M governor put it on and it runs like a new tractor. I had to replace the throttle plate screw as it was only half a screw and also now when I hit the ignition switch it shuts off. Could be when the linkage was messed up it would not let it die. Good thing is I got the sweet corn in now just need rain.

Glad it worked out. It certainly seems to me like something is missing in the part of the story about your ignition supposedly not shutting it off, but if it works for you that is all matters.

 

[BarnyardEngineering]

Well we are back online again, I went to the local salvage yard and got a good used M governor put it on and it runs like a new tractor. I had to replace the throttle plate screw as it was only half a screw and also now when I hit the ignition switch it shuts off. Could be when the linkage was messed up it would not let it die. Good thing is I got the sweet corn in now just need rain.

You are welcome to some of our rain... We don't need any more for a while.

 

[mailman1]

In regards to the ignition problem and a former post about high idling I tried it this AM and before I could get my foot off the starter it was running which I haven't had happen for a long, long time. I think a combination of a worn governor throttle shaft and a worn throttle plate screw affected the engine from not wanting to shut down because this morning when I pushed the ignition switch in it quite immediately where as before it would keep running and I haven't changed anything on the ignition.

 

[used red MN]

In regards to the ignition problem and a former post about high idling I tried it this AM and before I could get my foot off the starter it was running which I haven't had happen for a long, long time. I think a combination of a worn governor throttle shaft and a worn throttle plate screw affected the engine from not wanting to shut down because this morning when I pushed the ignition switch in it quite immediately where as before it would keep running and I haven't changed anything on the ignition.

You never answered if it has an alternator or a generator. Unless there is some extremely unusual circumstances a spark ignition engine stops firing the cylinders when the power is turned off to the coil and the spark is stopped. even if the carb is pinned wide open. When shut off there may be some slow chug-a-dee-chug when it spins down near idle speed and diesels, but that type of run-on is never close to being fearful of it blowing up from over-revving. The “extreme circumstances” are something like a guy that posted a while back running an old Case on a grain dryer. Something happened an it lost coolant. When he came back and found it he claimed the head was glowing red and I forget what he said he did to stop it but it was evidently hot enough to vaporize the gas and light it under compression. My guess is that something must occasionally be back feeding your ignition, likely incorrect alternator wiring if it has an alternator. Since you fixed the governor to carb connection problem you probably won’t have any more trouble with high rpm run aways. My guess is it may continue not shutting off occasionally because of a problem in the ignition wiring.

 

[m16ty]

A run away is when the rpm keeps increasing till the engine flys apart. Diesels are know for that. When they sniff gas in the air.or a faulty pump. The only way to shut them down is to block off the air intake. In A gas engine working hard it’s called run on. The way to cure this is to have the idle set as slow as the engine will run. Even completely closing the throttle plate. No air entering it cannot keep running. This talk of a run away engine here is confusing. I am sure it’s not running away. As said you have a back feed from the alt. Why not disconnect it to prove the point.

It can also happen with a turbo failure dumping oil into the intake. I had this happen to me one time.

 

[used red MN]

It can also happen with a turbo failure dumping oil into the intake. I had this happen to me one time.

Correct, but only on a compression ignition engine/diesel, NOT a spark ignition engine.

 

[mailman1]

Sorry I forgot to mention that it was converted to a 12 volt alternator system for starting maybe 20 years ago and I have never changed any wires aside from replacing the ignition switch when I thought it was bad. Anyway I'll keep a watch and see if it acts up any more or not. Thanks for all the ideas and help on getting this resolved.