Farmall C wont shut off

Hi
This is in regards to yesterdays discussion about the C possibly dieseling. I'm not sure if the owner described it right or if that actually was the problem, I was just going by my past experience. Usually when you start up a fresh overhaul you turn up the idle and turn the dist to where it will fast idle the best to keep it running and warm it up good before making any final adjustments. Every engine act different but if you shut it down to tighten up some stuff it will probably run on with no help from the ignition system. What I am trying to get at ( correct me if I'm wrong) is they call this dieseling because like a diesel engine after the glow plugs have done their job and are shut off by the glow plug controller the engine continues to run without the aid of the plugs. Been a long time since I messed with one of these, am I right or wrong?
Bob S.

Yeah Bob S - it's called dieseling because ignition occurs as within a diesel engine - ie. without the aid of spark. A quick review:

Running can be caused by one of 2 fundamental causes -

1 - Ignition spark continuing after the switch is shut off

2 - True "dieseling" - fuel/air charge ignited by something other a spark at the spark plug.

Causes for #1 can be the ignition coil being backfed from another 12 volts source - usually the alternator on an improperly wired 12 conversion - or (occasionally) by a bad kill switch on a magneto-equipped tractor.

Dieseling OTOH is caused by something in the combustion chamber remaining enough between power strokes to spontaneously ignite the fuel air mixture when the piston is near the top of the stroke - even though no spark is present.

Distinguishing between the causes is usually very easy. An engine with backfeeding coil or bad kill switch will generally continue to run pretty much unchanged (ie smoothly) after hitting the switch.

A dieseling engine however will run erratically, usually missing on a few cylinders and with a distinct metallic knocking after the ignition killed.

Common causes of dieseling is foreign matter (a bit of carbon or a piece of head gasket protuding into the cylinder) that becomes heated red-hot during engine operation.

Other possible causes are using spark plugs several heat ranges too hot, having the idle RPMs set too high, not fully closing the throttle before hitting the kill switch, use of low octane gas in a high compression engine (not a problem with a tractor engine!), low coolant causing a grossly overheated engine, etc.

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Incidentally - and contrary to the opinions of some - changing ignition timing has NO effect whatsoever on dieseling. Very simply there is no spark to time when the ignition is shut off. Consequently "ignition timing" becomes a meaningless term.

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Make any more sense now?? ...Bob M

dieseling -runs without a spark to ignite the fuel. in a diesel engine the intake air is com pressed so much that it gets hot enough to ignite the diesel sprayed in by the injectors.the glow plugs aid in starting a cold diesel engine.

Bob, thinking that I might be among the "some", and realizing that my earlier post had a tone harder than any I meant to take on teddy, my only argument for ignition timing contributing to dieseling is that if it's retarded enough to overheat the head after the engine has run for some time at speed, that overheating can add sufficient heat to the cylinder to contribute to dieseling (i.e., heating up carbon or metal burrs, or the whole environment, enough to ignite small amounts of residual fuel) that wouldn't get that hot with good timing. Seen it enough times with motors timed "by ear" not to suggest it as a cause.

I am not speculating and would not suggest that a mistimed spark is firing the motor after it is disabled (apart from the backfeeding issue which, of course, has nothing to do with timing).

Howdy
I'm only going on with this as there is still a difference of opinion and I'm sure C-Man might want to know how he fixed it, maybe ( after turning this and adjusting that ). ScottyHOMEy said , if I remember correctly, that spark timing retarded too much can cause an engine to run hot and cause it to run on after ignition is shut off. I on the other hand thought just the opposit, advancing the timing too much will cause this as well as advancing timing will speed up the engine. Remember, C-Man is talking about a fresh rebuild and when first starting them up there is drag on the deglazed cyl walls and you have to speed em up to keep em running. Just my opinion, I havent been a working mechanic for over 30 years ( I think they are called technicians now and they wear gloves )
Thanks Guys
Bob S.

Scotty
I guess that I was typing my latest entry while yours was already on the way. Sometimes these things go on forever and never do get resolved then after everyone blows a fuse and has smoke coming out of their ears the owner writes and says that he forgot to mention that he hot wired it to get it running and forgot all about that extra wire. But just to qualify myself, I worked in a few large GM dealerships in Milw for over 35 years and most all of the jobs in the place at one time or another and saw many odd things not found in the shop manuals or taught at the training center.
Bob S.

Scotty - You make a very good point - one I had not considered! Under certain conditions a grossly mistimed ignition COULD cause an engine to run hot enough after extended operation to cause dieseling at shutdown.

OTOH such situation would also be accompanied by some other somewhat dramatic symptoms: extreme knocking (timing too far advanced); glowing exhaust manifold/flames out of the exhaust (timing way retarded); extreme loss of power and overheating (timing too far out either way).

So I still submit it's probably not likely the average guy fooling with an old tractor will ever experience running on caused by bad timing.

I tried to respond earlier to your question, but the potty filter blocked me (I looked as hard as I could and darned if I could find an even marginally offensive word in it -- go figger!).

Retarding a spark (it may still be advanced BTDC, but not far enough) delays the combustion to the point that the valves open before the combusting fuel is done expanding, and it finishes burning and expends the rest of its energy in the upper part of the head. The net effect is that you have energy(heat) that has not been converted to motion. It thus remains as heat and overheats the head and can be pronounced enough to boil an engine over.

It is a new rebuild, so it's fairly safe to eliminate glowing carbon as a cause, as well as burrs. Since you've said the motor has been heated up, I'd suggest warming it up again, set the high and low idles as well as the load mixture, shut it down, retorque the head, run the valves, and see how it behaves.

These motors, in my experience, will fire right off after a good rebuild. They do require to be worked to seat the rings properly, but really don't need to be wound up hard to get or keep them running.

That said, most of us, as long as the teeth are in place on the gears at the front, use the same ones that were there, but there is enough slop in them from the years of use that there is often some benefit to doing a little timing by ear once it's running, as those gears, from the crank to the cam to the governor/distributor shaft, will have developed some slop. That's where the danger of retarding the timing too far comes in.

As a last step, after retorquing the head and running the valves after you've had it running well, I'd suggest you re-check the static (dead-stop) timing against what was done with the motor running.

Bob,

I've gotta be careful here, I've got Bob M and Bob S both goin' on at once, but I respect you both.

I said in another post with someone the other night that it's difficult sometimes to offer advice without offending, because you never know how much experience comes with the question. I said something then to the effect that you don't know if it's someone like TractorVet or Bob M, consummate pros in my book, or somebody with no more than a screwdriver, a claw hammer and a pair of pliers. So . . . my apologies. It is never my intention to insult anyone's experience or intelligence. I just wish I could remember what it was that finally made it stick with me that it is over retarding a spark that will overheat a head sooner than too much advance (which is usually limited by the advance mechanism). Lost in the mist of time, but it's stuck.

Please let us know how you make out with this one. I'll be all ears.

I hear ya, Bob. Trust me, you're one of the last guys around here I would ever try to argue with. I think I've said it before, though maybe not directly. Your experience and your willingness to share it (along with access to your library of wiring diagrams) has helped more people who have googled onto this board than I could ever hope to.

On the particular topic at hand, I've seen those cherry red manifolds go hand in hand with boiling over and dieseling (usually with a big backfire at the end when the old girl decides she's done). Whether they were tractor or car motors, in almost every case a check of static timing turned up an error in the ear of the fellow who tried to time it by feel/ear/hand, and wound up with the spark retarded.

I'm gonna watch this case to see what turns up.

Scotty
Where do I begin? I guess by not explaining Myself I have led you and others down the wrong path. I am not the guy with the problem nor am I working on his tractor. He (c-man ) posted on the 12th with the "wont shut off" question, I replied "could be ---idles too fast and/or timing is off". Teddy replied "timing has nothing to do with it", to which you said yes it does. All I was trying to do was get an answer for C-man whereever he might be, I figured he would join in on this discussion and give a better explanation of his problem, but no such luck, he might be out somewhere throwing wrenches at his tractor. If I have caused any problems here it sure was not my intention.
Thank you
Bob S.

i also worked at a GM dealership as mechanic in late 70s and 80s . to cure dieseling the idle had to be slowed down. thats why GM had electric idle solenoids on the carburators. you set the carb idle screw so the throttle plates were completely closed or next to it then the idle was adjusted with the electric solenoid adjustment to get your idle speed. then when you turned the key off power was cut to the solenoid which resulted in the throttle plates closeing preventing dieseling . example the 427 was bad for that. it was more of an idle thing than timing . timing was checked also and if anything it would be set a couple degrees to the retarded side from the factory setting. and yes advancing timing increases engine RPM.my experience with dieseling is your idle is set too high. slow it down and problem solved.

I, for one, really enjoyed the discussion among the three of you. I conclude that each of you are correct in every post. Please find another topic and go at it again. Some of us lurkers may learn something. good going. bob f.

I fixed it !!!! I just reset the idle screw in the carb. The old tractor has not ran in 15 years and it now purrs like a kitten. I already plowed the garden for the winter. Thanks for all the information. I just love reading these post. I don't have a lot of time to do that but there is alot of information on here.

Good job!