MD started on gas when pulled, still more questions

SW EM · Jan 7, 2017

Making progress, but still trying to understand why it won't fire using its starter...

When pull-starting, a higher cranking speed would generate more cylinder pressure which could help with starting. It would also advance the spark possibly in the mag.

Last night I inspected the centrifugal weights on the magneto. I turned the pin 180 degrees that they catch on when hand cranking because there was a little wear. I reinstalled the mag, checked the static timing, and tried to start it with the starter. Small puffs of white fog (looks to me like unburnt gas) came out of the exhaust pipe.

I will see if I can get a set of new Autolite 388's today and try them. I can't understand why a spark plug would function when pull starting, and when out of the head hand-cranking to check for spark and timing, but not within the cylinder head at slow cranking speeds.

Any input is appreciated!

jim warehime · Jan 7, 2017

What size and cca battery you using?

SW EM · Jan 7, 2017

12v 850 cca battery

Is there supposed to be some sore of "spring" that forces the centrifugal weights outward in the mag? Then at higher rpms the weights counter the spring force and the impulse disengages??? I just saw a pic online of someones and I do not have that. I just have the 2 weights held on by a retaining snap pin with a washer.

notjustair · Jan 7, 2017

Of course I know there is a remedy, but I have known two machines in my life that would only start when pulled. One was our old Farmall H that
we ground feed with. It never once started itself that I remember. We just pulled it and used it. It idled all day in the field with the grain cart
during harvest. Another was a 47 Chevy grain truck. It had a chain wrapped permanently around its front bumper. I'm not sure why, but it was
the same way.

Machines are like people - some have given up and just have to be forced into doing their job!

I've been following this saga hit and miss so forgive me if you mentioned this. It doesn't pop with fuel in the plug holes. To me that's timing. I
know you looked it over. But have you tried getting it running and adjusting the timing by ear? If it will run fine once pulled it has to be
somewhere in that slow revolution timing sequence I would think. Have you pulled plug wires while it's running and swapped things to verify
that everything is working where and how it should? This one is a puzzler and I feel like if one of the guys could just see the sequence they
would have a whole new insight.

mschwartz · Jan 7, 2017

I don't have a picture handy but I think you are on the right track. I have had two tractors that I could only start by pulling and both had
problems with the impulse coupling, either dirty and stuck or broke or missing parts. Keep in mind that I think the diesel mag will be mirror
image of most pics you are likely to find on web, don't ask how come I remember that! Good luck.

Tom Fleming · Jan 7, 2017

If the impulse is not working correctly, it will be a rare bird that will start with just the starter. I believe someone has already stated this, but I'll recap just to be safe.

Diesel H4 mags turn counterclockwise. Also, the internal timing must be set correctly. There are 2 marks on the drive pinion gear inside the mag. One is for clockwise rotation (gas engine), the other is for counterclockwise (diesel). That pinion MUST be on the correct timing mark.

Honestly, for the symptoms you are describing, I believe your impulse is the problem. If you can pull start it, you are spinning the mag fast enough to produce a hot spark, enough to start and run. A defective impulse will not spin the mag fast enough to start the engine at starter cranking speeds.

old · Jan 7, 2017

Forget the auto lite plugs and get a set of NGK plug that match those auto lite and I bet it is more likely to fire up then with auto lite plugs. Now days auto lite plugs and junk. Every time I need to replace plugs in my machines I am going with the NGK and have had better luck with them then champs or auto lite plug

D Slater · Jan 7, 2017

Think you looked at a gasoline mag. Are you sure the impulse coupling trips and speeds up just after TDC.

gene bender · Jan 7, 2017

There isnt any cent wts on your mag moving parts on the impulse could mess things up. Your problem sounds
like the rotor is not timed with the tower when it fires thats why when you pull the tractor it will start.
You need to make sure the piston is at the top of compression stoke removing the plug and looking in with a
mag lite you can see when the piston is at the top then the rotor should be pointing at the tower of #1
plug mite need to remove the cover so you can time the gear to get the rotor in the correct position. I do
runinto this problem as sometimes when they replace the points they take off the wrong place then get rotor
out of time tooth or so then have hard time starting.

David G · Jan 7, 2017

I would agree with concerns on impulse working.

Can you crank tractor by hand and check for the snap?

SW EM · Jan 7, 2017

(quoted from post at 18:32:20 01/07/17) I would agree with concerns on impulse working.

Can you crank tractor by hand and check for the snap?[/qu
ote

Yes the impulse snaps when hand cranking it, that it how I timed the mag. It sparks on all 4 plugs when they are out of the tractor. The rotor is timed to the "L" mark. And it runs when pull started but not crank started. Was wondering if the impulse was kicking out a lower rpm than it should be.

The picture of the counter weights I saw may be for R-hand mag, but they should still have the same parts, just opposites. His looked like the was a small spring mechanism the kept the impluse catch part of the weight outward against the catch pin.

Bob M · Jan 7, 2017

Your problem may be the plugs. Autolite 388, Champion D21, etc. is NOT the correct plug for the MD.

Rather the Champion D89D or equivalent (extreme extended tip) was specified by IHC. They place the fire deep inside the starting chamber to facilitate starting.

They are hard to find, and spendy when you can locate 'em - around $10 - $15 apiece last time I looked.

TractormanNC · Jan 7, 2017

I agree with Bob M. Get a set of the correct D89 Champions and put em in. (as much as I hate to recommend Champions)

jim warehime · Jan 7, 2017

The autolite 388 is a cross over from a champion D89D or modern number 543. I use 388s in both my md's and never have a bit of problems.

jim warehime · Jan 7, 2017

Just a thought, didn't you have this engine
all apart? you say you timed the mag with
the engine at TDC using mark on pulley?
There are 2 marks on that pulley, and have
you checked to make sure #1 is really at TDC
when the marks on pulley say it is? Again
thinking outloud.

jim warehime · Jan 7, 2017

Correction it is autolite 379 in my diesels just looked to be sure.

jim warehime · Jan 7, 2017

Here is a list of plugs that the d89d crosses too.

Dennis K (WA) · Jan 7, 2017

SW EM, The caseih parts site shows an exploded view of the mag.
You should be able to determine from that if you have missing parts. I think there should be springs attached.
Has to be frustrating, good luck.
Dennis

Janicholson · Jan 7, 2017

I will ask you to pull the plug wires and put old plugs (Any) on the ends. Ground them, and run the starter. if theydo not
fire, the answer is in the mag impulse. There is no relationship between the compression and it not running. engines with
20psi will start. try a compression test on a gas M when hand cranking.!!!. Jim

Tom Fleming · Jan 7, 2017

I am with Jim. Just because it snaps, doesn't mean the spring isn't broken or worn out. Also, are they copper cored wires? If they are not, replace them with copper plug wires. Composite, graphite core wires are a BIG NO NO with magnetos.

SW EM · Jan 7, 2017

Running D89D plugs now. Yes, the implulse is timed to snap at the "M" notch on the pulley. Verified by pulling spark plug and watching it spark at the mark too. Runs when pull started.

I'm going to pull start it and bleed the injectors individually today. Then try to switch it over to diesel.

SW EM · Jan 7, 2017

Plugs wires are brand new out of box. I think they're copper core, I'll double check.

The large spring is intact, clean, and provided good resistance when turning the mag my hand. I'll post pics of everything tonight!

D Slater · Jan 7, 2017

Diesel doesn't use the small springs on impulse pawl that a gas does is what I meant. Washer and clip on diesel. Look up Farmall MD on the online parts site. Go to electrical, then # 122 for a diesel mag and # 091 for a gas.

Janicholson · Jan 7, 2017

An impulse coupling that works when hand cranking, may not work at electric start cranking speeds. Even though it was 12v to
begin with, a faulty impulse catch can prevent the latching except at near zero Rpm. The spring that engages the pawl for
impulse latching must be strong enough to hold the weights in at starter motor speeds. Jim

used red MN · Jan 7, 2017

What Jim is saying are my exact thoughts. I am not familiar with the diesels so I did not chime in. Not sure how the crank pulley is marked or what the marks represent. If one of the marks is X degrees advanced and one is TDC. During normal rotation the first one that lines up is the advanced mark and the 2nd is the TDC mark. Again, not trying to play the "dumb card" just want to find a possible error that may be at the heart of the problem.

SW EM · Jan 7, 2017

I have had the diagrams of the mag printed off and they didn't show the spring clip that I was talking about. Thanks for clearing that up!

SW EM · Jan 7, 2017

You are right about the 2 marks on the pulley. My first one says "DC" I believe, then the second one "M". The book says to time it statically to the "M".

I pull started it multiple times today. It pops right off after about 3-5 fast turns of the engine. Bled the whole system up to the injectors, but could never get anything out of them...I controlled the lever at the pump and moved it through its full range of motion and I couldn't tell any change at all (engine speed, exhaust). I am getting really good pressure at the gauge though.

Janicholson · Jan 7, 2017

The plunger is likely stuck. The components will come apart without taking the pump off. A bit of carb clean and gentle
tweaking with a screw driver. Inside the pump is a rack that controls the amouny of fuel if it is stuck (won't move with the
hand lever from the drivers seat) it can be freed with patence and solvent and patence. do not force it things will break.
Easy effort, and solvent applied with care. Jim

SW EM · Jan 7, 2017

Any tips on removing the fuel lines from the injection pump? They seem pretty tight. Manual says I need a special tool?

Janicholson · Jan 7, 2017

A crows foot line wrench is best. A standard line wrench can work. Jim

rustred · Jan 8, 2017

the whole purpose of the impulse coupling is to start the tractor at a slow cranking speed. if it is not working you will not get the spark hot enough to fire the plugs. any tractor with a mag and no starter always start easy is my experience. to get the mag to fire the plugs the tractor must be pulled when the impulse coupling is not working.
plug makes have nothing to do with starting the tractor... but the engines must have the long reach plugs in them. the standard gas plugs will work but it makes starting hard. i did this experiment to prove that they will start. once running there is no noticeble difference. basically one set of plugs will last the entire tractors life. as they are hardly used. plugs can be cleaned , the electrode filed flat and regapped and its as good as new. seen many good plugs go in the garbage can. another experiment u can do is use another vehicle or tractor to fire the plugs, to make sure they are not dead. and it takes more to fire a plug under compression than out of the head.
and the points must be gapped and clean also and good condenser.

BarnyardEngineering · Jan 9, 2017

In a previous thread you said the compression was between 50 and 75 PSI. That's going to make it tough to start with the starter even if everything is spot on and working correctly. You've been through the ignition and fuel systems enough times that I've got to believe there is nothing wrong there.

SW EM · Jan 9, 2017

I think the problem is with the magneto impulse, or low compression. However some people have responded saying that my compression values checked out OK for a gas start diesel. I know now that it isn't getting diesel fuel to the injectors because the rack and plunger are stuck. Currently trying to take apart the plunger to clean. What a bear....its soaking in acetone for a few days.

BarnyardEngineering · Jan 9, 2017

I feel like I said this previously, but being a gas start diesel does not exempt it from the basic principles of internal combustion. A normal gas engine won't start for beans with much less than about 75PSI compression.

DanMD · Jan 9, 2017

(quoted from post at 20:22:22 01/09/17)
I think the problem is with the magneto impulse, or low compression. However some people have responded saying that my compression values checked out OK for a gas start diesel. I know now that it isn't getting diesel fuel to the injectors because the rack and plunger are stuck. Currently trying to take apart the plunger to clean. What a bear....its soaking in acetone for a few days.

I am not an expert on compression numbers. I can tell you my SMD had gas compression values in the 90's before I overhauled it. It was blowing a lot of blue smoke like this. After I had it overhauled with new everything, my numbers are in the upper 120's.

Dan

DanMD · Jan 9, 2017

I need to edit my last post after I went and looked at my notes. My compression readings were 105 to 130 before my overhaul. It was blowing blue smoke and started ok. After the overhaul, they are all in the upper 120's. I don't think your readings are good.

HTH,
Dan

MD started on gas when pulled, still more questions

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