Farmall M Engine Problems

1943 M. Over time it got slower and weaker and was getting Antifreeze in the oil. One time, we advanced the timing and it ran ok for awhile but still sounded weak. Eventually it got so slow and weak that it wouldn't stay running. I noticed that it always blew some vapor back out of the carburetor. I assumed it had a burnt or sticky intake valve. I pulled the head and had it totally rebuilt at a good machine shop. The head was trashed from "burning" water for years. It was surfaced, new valves, springs, seats everything. It was magnafluxed and did not have cracks. The machinist said the head gasket was blown. The block surface looked very good. Cylinders and pistons appear to be good. I installed a new head gasket and put the head on. It blows out of the carburetor even worse now. I have good hot spark and good fuel at the carburetor. It blows out of the carburetor so much that the plugs are not getting wet from fuel. I know the carburetor is getting fuel because it blows a nice vapor back out of the carb. Also when I put my hand over the exhaust, I can feel an inward "suck" as well as blowing. If we shoot starting fluid into the carb and hold a hand over the intake on the carb, the motor will pop and hit a few times. I have turned the motor to TDC on all of the cylinders and blown air from the compressor into the spark plug holes and none comes out of the carb (so the valves are seating). When I turn number one cylinder to TDC, both rocked arms are loose and the valves are closed. Could this have jumped timing so bad that it's 180 deg. off? Any other ideas? It's going to be a job pulling the timing cover off to look inside. Sorry for the long story, but I cannot figure this one out!

Sounds like the intake valves aren't adjusted properly.

I am not sure if this is your exact problem but I have had this exact thing happen before on an A farmall and something similar happen on an M. Pull the distributor and rotate the engine over while watching the timing gears. I had an A the broke a few teeth off of the timing gears and the tractor would run good until the broken teeth lined up just right and it jumped timing. Replacing the timing gears cured he problem in the A. On my M when I pulled the front cover to pull the cam I noticed the it also had some teeth broken on one of the timing gears, so this very well could be your problem as well.

Edited original post to replace "the" with "that" in 2 places. I am still trying to get used to this new laptop
I am not sure if this is your exact problem but I have had this exact thing happen before on an A farmall and something similar happen on an M. Pull the distributor and rotate the engine over while watching the timing gears. I had an A that broke a few teeth off of the timing gears and the tractor would run good until the broken teeth lined up just right and it jumped timing. Replacing the timing gears cured he problem in the A. On my M when I pulled the front cover to pull the cam I noticed that it also had some teeth broken on one of the timing gears, so this very well could be your problem as well.

I would agree on post below. When I first got my SMTA it started hard and just didn't run right no matter what I did. On advice from someone here I removed distributor and hydraulic pump and found the timing gear wobbled around. There was a chip off of the end of the camshaft I assume from timing gear getting loose.

The early Ms had an aluminum timing gear that was good enough. But in some cases the retainer gets loose and the gear hub wears on the shaft causing slipped timing of the valve train. It can be struggling along getting worse and worse, till the cam is so far out of time with the pistons that it just won't run. the intake and exhaust valves are designed to have a tiny bit of overlap when the piston completes the exhaust stroke (TDC exhaust). If you remove the Valve cover, and watch the moment that the overlap on #1 happens, you then can see from timing marks, or piston location (with a plastic straw in the spark plug hole) where the piston is in relationship to where it should be (very close to TDC. The timing marks are on the crank pulley, so they reflect piston location. If it is out of time, putting a new gear in it from a 450 will strengthen the drive considerably. At that time you could replace the front cover with a 52 or newer cover, and install a live Hydraulic pump between the distributor and cover (from a Late SM, SMTA, 400,!! Jim

Plug wires mixed up or bad cap?

I want to add that my 1942 M did not have an aluminum gear, it was definitely cast iron and was missing a couple teeth maybe more, I just can't remember, it's been about 8 years since I had it apart.

(quoted from post at 13:33:55 11/14/15) The early Ms had an aluminum timing gear that was good enough. But in some cases the retainer gets loose and the gear hub wears on the shaft causing slipped timing of the valve train. It can be struggling along getting worse and worse, till the cam is so far out of time with the pistons that it just won't run. the intake and exhaust valves are designed to have a tiny bit of overlap when the piston completes the exhaust stroke (TDC exhaust). If you remove the Valve cover, and watch the moment that the overlap on #1 happens, you then can see from timing marks, or piston location (with a plastic straw in the spark plug hole) where the piston is in relationship to where it should be (very close to TDC. The timing marks are on the crank pulley, so they reflect piston location. If it is out of time, putting a new gear in it from a 450 will strengthen the drive considerably. At that time you could replace the front cover with a 52 or newer cover, and install a live Hydraulic pump between the distributor and cover (from a Late SM, SMTA, 400,!! Jim

Click to expand...

First thing I would try is line no 1 cylinder on TDC ( using a straw through the plug hole), then remove distributor & turn 180 degrees out & re-install.

Thank you all for your help and new ideas. I would like to add that this tractor does have a hydraulic pump in front of the distributor.
The tractor has a loader that runs off this pump. I looked on tractordata.com and set the valve clearance to .017 intake and exhaust.
Sounds like I'm going to pull the distributor and pump off and have a look around inside at the timing gears.

Ive had more Ms apart than I can count and don't recall ever seeing one with an aluminum gear. Having said that, what your problem "sounds" like to me is first the points are/were wore out or woere out of adjustment, and now you have the plug wires on wrong. Before tearing anything apart, double the check the firing order, and check the points.

Oh well not aluminum. But weak in the Knees. Sorry, Jim

DieselTech should be able to tell you what degrees the intake and exhaust should open on #1, just take the firing order and add 90 degrees for each subsequent cylinder. It really sounds like you have a valve issue. I would double check the valve clearance after you verify the valve timing. I would also recheck the rotor position to make sure it is on #1 when the engine is on TDC for #1 on compression stroke.

It is important to remember that the cam rotates 1/2 as fast as the crank, so there is a TDC on compression and one on exhaust for each cylinder.