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M37 Still Won’t Start – Not Sure What To Look At Next

plym49

Well-known member
1,164
171
63
Location
TX USA
I reread your post. Check that there is not sediment in the bottom of the carburetor bowl. After some driving, sediment that has settled can block a jet from being agitated.

The same thing applies to the fuel intake inside the tank. A piece of electrical tape or something might be getting sucked up after some driving. Park and it floats away - rinse and repeat. The glass sediment bowl might not show as empty if this is happening.

Next time it quits, remove the fuel line at the carb and crank the motor. See if fuel spurts out.

If not, squirt a little ether down the throat and see if it kicks. If it does it is not an ignition problem.
 

Travlr

Member
56
58
18
Location
Middle a Utah
After months of work I still can’t get my M37 to start and could use some advice.

Prior to doing all this work the vehicle ran but would just quit after 15-30 minutes. (usually at a very inopportune time).
Here’s the parts I’ve changed so far:

1) Gas tank had rust – so removed and had it completely restored
2) Changed the fuel lines as a precaution
3) New Fuel Pump
4)
New in-line Fuel Filter
5) New distributor
6) New spark plugs
7) New spark plug cables
8) New carburetor


So at this point, I know for certain I have fresh clean fuel at the carburetor (I can see it in my in-line glass fuel filter) , I have verified I have high voltage coming from each of the spark plug wires (spark jumps about ¾ of an inch without issue). I thought I may have installed the new distributor backwards to I took it out and rotated the shaft 180 degrees, no change. I guess I am now suspicious that my new carburetor may be at issue – I just don’t know what else it could be. I have a couple of small backfires – not sure if that is any indication of the issue. How can I verify I have a good air/fuel mix making into the cylinders?
All else failing, I'm going to have an engine for sale soon, probably fairly cheap.
 

Mullaney

Well-known member
Steel Soldiers Supporter
Supporting Vendor
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After thinking about the disappointing compression results and reading some of the comments, I figured I’d press on with trying to get it going again today. I decided to start at ground zero and hopefully not overlook anything.

1. Is there fresh fuel in the tank – YES
2. Is the oil level proper - YES
3. Are the batteries fully charged and at the correct voltage – YES (charged last night and measured 25.4VDC at the terminal on the starter motor)
4. Is the fuel making it to the carb – YES (visually see it in the clear fuel filter I have about 6 inches from the Carb (BTW - This is the only non-military, non-standard thing under the hood)
5. Is there fuel in the carb – YES (I drained the bowl which had fuel, then cranked the engine for 4 seconds and removed the drain plug again - the bowl was again full)
6. Verified I had 25VDC at the input to the Igniter assembly – YES (Measured 25VDC with the ignition in “ON”)
7. Is the Igniter working? YES – (Removed the spark plugs and connected them to the ends of the spark plug cables – the nice thing about the water tight spark plug cables is you can easily see the spark for each plug firing this way since the jacket brings the ground to the plug – I confirmed all 6 plugs had a spark and spark color was blue/white )
8. Is the firing order correct? YES, BUT…(I Verified the sparkplug cables are all going to the correct points and that the firing order is correct – HOWEVER since I had replaced the entire igniter assembly it is possible that the cam that connects to the engine is 180 degrees out of phase)
9. Is the engine compression OK? NOT SURE- (Since I am not able to run the engine to ensure all the rings and cylinders are well drenched in oil, I have to rely on the results that are showing ne between 60 and 90 psi which is low – As was brought up by one of the folks this is probably OK – It was working previously I don’t think anything really dramatic changed since the last time it worked)
10. At this point I believe the fuel side is good and the electrical side is in order should work.
11. Took Fuel cap off to prevent a possible vacuum in the tank.
12. Pulled the choke out all the way, verified on the carburetor that the choke lever did move.
13. Turned on the ignition power and engaged the starter……
14. Engine will still not start, not even the slightest hint of ignition. Tried the following:
a. Removed Air Filter and verified suction while my son engaged the started – OK
b. Verified air is exiting the exhaust – OK
c. Sprayed starter fluid in air-intake throat – NO EFFECT, not even a hint of ignition – Tried this a number of times…
15. Turned the ignition to “OFF” -Took the top half of the igniter housing off and made note of the position of the cam. Removed screw from the timing advance arm and removed the bottom half of the igniter assembly from the engine block. Rotated the igniter cam shaft 180 degrees and reinserted the assembly back into the block. Verified the cam shaft had properly seated then secured the advance arm back to the engine. Had my son engage the started (with ignition power off) to verify that the cam was properly rotating. Reattached the top half of the igniter assembly.
16. Turned the ignition “ON” and again tried to start the engine, still won’t catch, not even a hint of ignition. Tried starter fluid, still nothing.
17. I’m really puzzled - Seems like I have good fuel and spark. Even if the timing is off I would think I’d at least get some form of ignition going.
.
Suggestions:

Hate to hear that your truck isn't cooperating... Not going udden udden can make a person pretty grumpy in short order. The backfire sounds like a timing problem. You mentioned rotating the distributor 180. That should have made it not crank at all. It might be worth KNOWING that you have the distributor in there right. Remove the coil wire, then Pull #1 spark plug. Takes two people, but somebody turns the motor over with your thumb covering the spark plug hole (not in it!). You should hear and feel a loud hiss and you are on the compression stroke. KEY is to not fly past the compression stroke and be on the exhaust stroke. Might have to do this test several times until you are SURE you are on #1's compression stroke. ...

Either with the hand crank or a big socket, rotate the motor slowly until the timing mark on the balancer aligns with the pointer. Then open the distributor cap. The rotor button should be pointing very close to the #1 spark plug wire. If so, your distributor is installed correctly. If not, it is time to move wires or rotate the distributor shaft.

Once that #1 wire is in the right spot, check the others to be certain that you have the firing order correct. There is more, but this is a "rough enough to crank" setting.

-----------

Silly questions:
New fuel pump and new filter and work on the tank. You did a lot there. You even mention seeing fuel move in the glass filter. Any chance that you could connect a pressure gauge to the fuel system up front?

Fuel & Air mixture screws are generally set by the rebuilder or the factory. Most carbs are tested, but maybe not these days. The screws on the base could be checked. GENERAL RULE is all the way in, then back out two full revolutions. BE SMART and count the rotations in to zero before you make any adjustments.

Maybe some pictures of the carb?

Near the top of your post it runs for 30 minutes and quits. Does it still do that, or will it just not crank at all now? If that run and die thing happens, it could be vapor lock. Maybe some of the other guys will pitch in too - but maybe gather a little more info with the stuff above and post that?

Never did see any pictures of the distributor or fuel pump and maybe even the top of the fuel tank? Maybe just a hand full of engine pix too for confirming firing order etc?
 

joseph m37

Member
26
27
13
Location
michigan
.
Suggestions:

Hate to hear that your truck isn't cooperating... Not going udden udden can make a person pretty grumpy in short order. The backfire sounds like a timing problem. You mentioned rotating the distributor 180. That should have made it not crank at all. It might be worth KNOWING that you have the distributor in there right. Remove the coil wire, then Pull #1 spark plug. Takes two people, but somebody turns the motor over with your thumb covering the spark plug hole (not in it!). You should hear and feel a loud hiss and you are on the compression stroke. KEY is to not fly past the compression stroke and be on the exhaust stroke. Might have to do this test several times until you are SURE you are on #1's compression stroke. ...

Either with the hand crank or a big socket, rotate the motor slowly until the timing mark on the balancer aligns with the pointer. Then open the distributor cap. The rotor button should be pointing very close to the #1 spark plug wire. If so, your distributor is installed correctly. If not, it is time to move wires or rotate the distributor shaft.

Once that #1 wire is in the right spot, check the others to be certain that you have the firing order correct. There is more, but this is a "rough enough to crank" setting.

-----------

Silly questions:
New fuel pump and new filter and work on the tank. You did a lot there. You even mention seeing fuel move in the glass filter. Any chance that you could connect a pressure gauge to the fuel system up front?

Fuel & Air mixture screws are generally set by the rebuilder or the factory. Most carbs are tested, but maybe not these days. The screws on the base could be checked. GENERAL RULE is all the way in, then back out two full revolutions. BE SMART and count the rotations in to zero before you make any adjustments.

Maybe some pictures of the carb?

Near the top of your post it runs for 30 minutes and quits. Does it still do that, or will it just not crank at all now? If that run and die thing happens, it could be vapor lock. Maybe some of the other guys will pitch in too - but maybe gather a little more info with the stuff above and post that?

Never did see any pictures of the distributor or fuel pump and maybe even the top of the fuel tank? Maybe just a hand full of engine pix too for confirming firing order etc?
also,check your coil, if those vent lines are n ot connected to the distributor housing,your coil may have overheated and is shot, they will work for a while then get hot and stop, another thing is do not leave the power switch on on the dashboard, that is energizing the coil and also will damage it,the vent lines arew htere to circulate air around the coil because its in a waterproof housing sealed
 

Travlr

Member
56
58
18
Location
Middle a Utah
.
Suggestions:

Hate to hear that your truck isn't cooperating... Not going udden udden can make a person pretty grumpy in short order. The backfire sounds like a timing problem. You mentioned rotating the distributor 180. That should have made it not crank at all. It might be worth KNOWING that you have the distributor in there right. Remove the coil wire, then Pull #1 spark plug. Takes two people, but somebody turns the motor over with your thumb covering the spark plug hole (not in it!). You should hear and feel a loud hiss and you are on the compression stroke. KEY is to not fly past the compression stroke and be on the exhaust stroke. Might have to do this test several times until you are SURE you are on #1's compression stroke. ...

Either with the hand crank or a big socket, rotate the motor slowly until the timing mark on the balancer aligns with the pointer. Then open the distributor cap. The rotor button should be pointing very close to the #1 spark plug wire. If so, your distributor is installed correctly. If not, it is time to move wires or rotate the distributor shaft.

Once that #1 wire is in the right spot, check the others to be certain that you have the firing order correct. There is more, but this is a "rough enough to crank" setting.

-----------

Silly questions:
New fuel pump and new filter and work on the tank. You did a lot there. You even mention seeing fuel move in the glass filter. Any chance that you could connect a pressure gauge to the fuel system up front?

Fuel & Air mixture screws are generally set by the rebuilder or the factory. Most carbs are tested, but maybe not these days. The screws on the base could be checked. GENERAL RULE is all the way in, then back out two full revolutions. BE SMART and count the rotations in to zero before you make any adjustments.

Maybe some pictures of the carb?

Near the top of your post it runs for 30 minutes and quits. Does it still do that, or will it just not crank at all now? If that run and die thing happens, it could be vapor lock. Maybe some of the other guys will pitch in too - but maybe gather a little more info with the stuff above and post that?

Never did see any pictures of the distributor or fuel pump and maybe even the top of the fuel tank? Maybe just a hand full of engine pix too for confirming firing order etc?
It's important to NOT TURN the air/fuel adjusting screws down tight. A lot of carbs have been ruined by turning the brass screws down tight and the needles being scored. A light touch to barely close them, and then two turns out.
 

Travlr

Member
56
58
18
Location
Middle a Utah
After months of work I still can’t get my M37 to start and could use some advice.

Prior to doing all this work the vehicle ran but would just quit after 15-30 minutes. (usually at a very inopportune time).
Here’s the parts I’ve changed so far:

1) Gas tank had rust – so removed and had it completely restored
2) Changed the fuel lines as a precaution
3) New Fuel Pump
4)
New in-line Fuel Filter
5) New distributor
6) New spark plugs
7) New spark plug cables
8) New carburetor


So at this point, I know for certain I have fresh clean fuel at the carburetor (I can see it in my in-line glass fuel filter) , I have verified I have high voltage coming from each of the spark plug wires (spark jumps about ¾ of an inch without issue). I thought I may have installed the new distributor backwards to I took it out and rotated the shaft 180 degrees, no change. I guess I am now suspicious that my new carburetor may be at issue – I just don’t know what else it could be. I have a couple of small backfires – not sure if that is any indication of the issue. How can I verify I have a good air/fuel mix making into the cylinders?
So did you ever get it running?
 

joseph m37

Member
26
27
13
Location
michigan
All else failing, I'm going to have an engine for sale soon, probably fairly cheap.
ok, stop what your doing, if the truck runs and then shuts off, its your coil, because these coils are sealed with the distributor,if there is no air movement the coil overheats,get another new coil do not use someones old coil because it to could be bad,and do not leave the power lever on on the dash, if you do you are energizing the coil and it over heats, and if you removed those 2 vent lines to the distributor put them back on, do not listen to guys saying you dont need them they are there for a specific reason and that is to get air to cool the coil because its in a sealed container, a lot of guys put posts out there and most of them really dont know anything about these trucks,try to get to someone who has the correct knowledge about these trucks and your frustration will be gone,we have ground up total restoration of several of these trucks and they run fine with all there original equipment as they were when they left the factory.remember they are simple vehicles,you need fuel,and spark,remember these trucks were in civilian hands for years and a lot o cobbling of parts,removing parts.because everybody thinks they know more that the engineers,any questions send a post
 

Karl kostman

Well-known member
Steel Soldiers Supporter
2,305
889
113
Location
Fargo ND
I had an M37 with problems very similar to what your experiencing and I went through the carb, point condenser and cap still no start. I talked to John at Midwest Military and he had me describe the type of coil in the truck and said they are BAD very unreliable so I bought a new coil from him and put that in and all trouble disappeared engine ran like a champ, my problem was the coil all the time!
 
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