Farmall MD no start update

SW EM

Member
I spent the day checking everything over and still cannot get it it pop once. I pulled all 4 plugs and grounded them to the frame, shut the shop lights off and cranked the engine and I had 4 good blue sparks. The magneto impulse clicks too.

I have tried squirting fresh gas in the spark plug holes, then installing the plugs. No difference really.

I must be getting a fuel from the carb because: the butterfly valve in the intake manifold is closed, the plugs I pull after trying to start it are somewhat wet with fuel, and it looks wet when I look through the spark plug hole. I am using AV Gas from the airport.

The valve lash has been set and checked multiple times. The firing order is 1-3-4-2 CCW looking from the seat. #1 cylinder fires at timing mark "M" on the crankshaft pulley when the piston is at the top of its compression stroke. Verified this by watching the valves. The valve cover is off while I've been doing all this. Could the spark plugs be grounding out while in the head???

The injector lines are unhooked from the injectors.

The decompression valves are about as far open as they can get it seems.

I notice that gas seeps from the bottom of the intake manifold gasket after I crank it for a while. I have tried using a combination of choking styles.

Tractor is sitting with the spark plugs out and decompression valves open tonight to let any gas evaporate that is in the cylinders. Maybe it was flooded?

Any help is appreciated! Thank you
 
Interesting problem. I read your other post and there are lots of good suggestions. Thought I might chime in with another possibility. I once had a Chrysler car that decided not to start, it was getting gas and I had pulled out a couple of spark plugs to see if there was spark. There appeared to be sufficient spark. After racking my brain for hours, I eventually replaced the main ignition wire between the ignition coil and the cap. The car started right up. The car had carbon/silicone wires which can fail with age. It takes less energy for the spark to bridge the spark plug electrodes in open air than it does for the spark plug to bridge the electrodes under compression in the cylinder. You might not be getting spark when the plugs are installed and the engine is compressing the air/fuel mixture in the cylinder. Just a thought. If you are using metallic wire spark plug wires then you likely don't have this problem.
 
Just a thought. I only had one M that would not start after checking everything as you did.
It turned out to be the rotor in the mag. It was off 2 teeth just enough that I was not
getting spark at the right time. once set right it fire right up. Check internal mag
timing. There should be a mark on rotor disc for cw or ccw L or R oldiron29
 

I had checked the rotor timing too. It is lined up with the mark "L" for the CCW rotation. There is a little bit of play in the notch that the rotor sets in.
 

This tractor requires special extended tip plugs, and I dont have 4 new ones to try....but I do have a new set of Champion D21's. I wonder if they would make an improvement.

I will use the compression tester today to get an idea of what each cylinder has. If it wasn't 0 degrees outside I would pull start it.
 
Get four corks that fit the spark plug holes. Repeat your test with the spark plugs out and the corks in the spark plug holes and confirm that the correct plug fires as the cork pops out of each individual hole as that cylinder comes up on compression.
 

Compression test on the MD was 50-75 psi. Cylinders 3 & 4 had slightly higher numbers than 1 & 2.

I don't know if anyone has a spec for the compression on the gas side. I couldn't find anything in the archives here.

These numbers do seem low if it were a true gas Farmall, but since it is only run on gas to warm up the engine maybe this is normal? Anyhow, I am going to try to pull start it and this will increase the compression more than cranking it. No diesel coming out of injectors yet. Sytem is primed up to the primary filter, and now the diesel tank is shut off until it starts on gas. I may turn it on before pull starting it.
 
I'm going to go out on a limb here and say your pull start attempt is going to be in vain, unless you
plan to try to start it on diesel. Which I would highly discourage abusing new rings and sleeves in
that manner. As I said before I am not that familiar with the diesels, but correct me if I'm wrong but
I don't think you can see the piston through the sparkplug is that correct? The reason I asked is I
would suggest verifying the cam is timed correctly. This would be done by turning the engine until
the number 4 cyl exhaust valve travel is reaching the closed position and the intake valve is just
beginning to open. At this point #1 cyl. should be very near top dead center and the mag rotor
should be positioned towards #1 cap tower. I'm not sure if these have a TDC mark on the pulley
that is why I asked about viewing the piston location through the plug hole, but you may be able to
do it by pulling the injector but I'm not sure. It seems that since the carb is drawing a suction that
the cam timing is okay but again looking for a "double check". One other thing is I think you are
saying that the plugs you are using are "good used" plugs? Aside from them looking wet do they
show any sign of black sooting? If so I would heat them good with a propane torch to clean them.
As said in another post the plug takes more voltage to fire under compression so they may be
shorting down the electrode instead of firing. If you have another known running MD it may be
worth pulling those plugs to try. Over all I am still leaning toward something is not timed correctly.
 
Wet spark plugs are fouled and will not fire when wet. You need to install new plugs or at the very least dry them off with a torch. If it where me I would take an old plug with me and buy NGK brand plugs that match and try them.
 
Warm those plugs with a propane torch to burn off any deposits. I dont think it will run or start with D21s in it. Av gas is much harder to ignite than 10% ethanol regular. Don't use it. More octane is less easy to ignite. Jim
 
It pull started and ran on gas. So that's a start! I think that it needs more compression at the higher cranking speed to fire.

I had fuel pressure at the guage. Bled the final filter. Then I had all 4 injector bleeders open, but nothing would come out. The diesel throttle was on a little bit too. I tried to switch it to diesel but it died. I figured that would happen since nothing was coming out of the injectors. Now that it is pulled back in the shop I read in the manual that the injectors need to be bled individually.

A day ago when I was cranking it with the injector lines disconnected from the injectors there were puffs of air coming out, with a rhythm, so I don't know if anything would be stuck in the distributor block.
 
Being a gas start diesel doesn't magically exclude the engine from the physical requirements for combustion. 50PSI isn't enough compression unless you're spinning the living daylights out of the engine.
 
I'll check the compression again now that it ran on gas for about 7-10 minutes. I shut it off on the diesel side to cool down.

There are quite a few places compression could be lost. I wonder if having the injector lines empty would allow any sort a back feeding? I would think that a injector is only a one-way
system.

A guy could squirt some oil in the cylinders, but I would think that would create another starting problem.
 
It is good to hear that it ran on gas. My feelings were apparently incorrect. Now I willl wait to see what the retest pressures are for the compression. One thought I have is maybe the ignition timing is late. If the engine spun fast enough during the pull start the mag advance would have kicked in. Now that is assuming the diesel mag is equipped as such.
 
That is normal compression for a gas start Farmall, they were, and are, hand crankable. Years of MD ownership. Jim
 
Run it on gas with the lines cracked at the injectors and the diesel speed lever about 1/4 open. This will pump fuel through the system. As soon as fuel starts coming out of the fitting, tighten it. If none does, it might have a stuck rack in the pump. Different issue. Jim
 
Buy a set of autolite 388 plugs. The D89D
crosses to these. They are cheap and work
great. Been using in a couple of my mds no
issues.
 
(quoted from post at 19:06:17 01/06/17)
Compression test on the MD was 50-75 psi. Cylinders 3 & 4 had slightly higher numbers than 1 & 2.

I don't know if anyone has a spec for the compression on the gas side. I couldn't find anything in the archives here.

These numbers do seem low if it were a true gas Farmall, but since it is only run on gas to warm up the engine maybe this is normal? Anyhow, I am going to try to pull start it and this will increase the compression more than cranking it. No diesel coming out of injectors yet. Sytem is primed up to the primary filter, and now the diesel tank is shut off until it starts on gas. I may turn it on before pull starting it.

I think your compression readings are low. I recently had my SMD overhauled and the readings in gas mode are in the 120 to 130 range for mine.

Dan
 
The new compression values are in the 75-90 psi range. I will look into the plug issue. Has anyone else had plugs that spark out of the tractor, but not when cranking with the starter. Then pull start the tractor and the engine fires off???

The impulse trips when hand cranking it, but could there be a way that the magneto advances the spark at much lower rpm's than usual? (I think it's supposed to be around 250 rpm)

A week or so ago when the mag was off the tractor I removed the nut which holds the drive member in place. The long magneto coupling spring was intact. I guess I didn't know much about how the advance mechanism worked at the time because I didn't look the weight/pawls over. When holding the mag in my hand I can move it around and hear the weights clicking around.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top