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

[Oldfart]

OK - Well today I started systematically going through all the various suggestions, and it looks like my number one issue is a major problem with compression (or the lack thereof). I measured each of the cylinders and the results were really disappointing.

Cylinder 1 90 psi
Cylinder 2 70 psi
Cylinder 3 90 psi
Cylinder 4 60 psi
Cylinder 5 70 psi
Cylinder 6 60 psi

According to the manual it should be between 90 and 130 psi with no more than 10 psi variation.

Wow – time for a big decision, pull the engine and rebuild it or to perform the operation outlined in Chapter 4 Section 2 paragraph 290 of TM 9-8030.

Just some thoughts from an old man. The compression is high enough for the engine to start. Oiling the rings and valves should help compression. Pulling all the plugs and then checking the compression will give a more accurate reading. If the starter is dragging and the starter crank speed is low, the compression readings will suffer. The valves are probably in time given that some cylinders are at 90 PSI. ~~~ It would make sense to me to find out why it won't start before rebuilding the engine or proceeding to paragraph 290. If you rebuild the engine, without finding the cause of the no start, it will continue to be a problem on a new engine. If the valves are in time with the crank, and there is sufficient compression (and there is enough compression to fire the charge) then there are only two things that can cause a no start. One is spark and the other is gas. A good spark should be 1/4 to half inch long and look blue not yellow. Proper timing for the M37 is 4 degrees AFTER top dead center, but it should start and run as far as 6 to 10 degrees advanced ~~ The first thing I would do now is to check to see how the sparks looks and assuming it is OK, then I would check to make sure it is coming at the right time to the right cylinder. If the spark is right and in time, then I would check the fuel by priming the throat of the carb with about a 1/2 ounce of gas to see if it would attempt to start.

If you move to paragraph 290, then take lots of photos and post them because I want to see how that looks for real.

 

[plym49]

I agree with OF. That is enough compression for the motor to start and run. The walss are probably dry from gas washdown from many attempts at starting, plus the rings get stuck. Once that motor sttarts and runs and you drive it some, the compression will be quite higher.

I do not think that the chain jumped a tooth because these motors do not tend to do that.

Have you brought #1 on the compression stroke and checked the timing of the dostributor? That is really the first step.

 

[plym49]

I'd just pop the cylinder head off and replace the head gasket, and then try the compression check again.

I seem to recall that these engines are bad about leaking around/blowing head gaskets. You should be able to see soot and maybe water where the head gasket is leaking if that is the case.

If anything, replacing the head gasket is a good thing to do, even if it doesn't fully solve your compression problem. (If anything it will eliminate one major variable.)

When these motors blow head gaskets, it is usually between the paired cylinders because the head gasket is very skinny at that point. The compression readings reported are not consistent with a blown head gasket. One of these engines with a blown head gasket will have readings like 50 psi in both paired cylinders. For example, if the readings front to rear were 90, 85, 95, 80, 50 and 50, then that would indicate a bad head gasket between 5 and 6. But note that the readings for those two cylinders would be very low and would read the same, since each would be dumping compression into the other.

Again, the OP's readings are not consistent with a blown head gasket.

 

[AN/GRC-46]

Wow – time for a big decision, pull the engine and rebuild it or to perform the operation outlined in Chapter 4 Section 2 paragraph 290 of TM 9-8030.

Paragraph 290 might be a lot of fun, but Paragraph 288 might be a bit more practical.

 

[M543A2]

The advice about the coil and condenser possibly breaking down is good. I think we are getting too far into it by getting too technical about this problem with pulling the head, valve timing etc. Your compression should run this old girl with no problems.
I did not see a note about whether or not you tried removing the fuel cap. If it fixes the problem, there is a little bar in the center of it that controls the vent. One setting is for fording. Turn it 90 degrees and it is for normal use. The fording setting closes the vent to prevent water entry. I have had two trucks that had the bar set for fording. They would run like you say, then draw a vacuum in the fuel tank and stop. If the tank is low on fuel, it will run longer than if the tank is full because there is more space it has to turn into a vacuum to stop the fuel supply.
If removing the cap solved the problem, turn the little bar 90 degrees and try again.
Regards Marti

 

[Oldfart]

Paragraph 290 might be a lot of fun, but Paragraph 288 might be a bit more practical.

I would like to see film of that as well.

However paragraphs 283 through 286 would be more to my liking if I was the end location.

 

[Oldfart]

The advice about the coil and condenser possibly breaking down is good. I think we are getting too far into it by getting too technical about this problem with pulling the head, valve timing etc. Your compression should run this old girl with no problems.
I did not see a note about whether or not you tried removing the fuel cap. If it fixes the problem, there is a little bar in the center of it that controls the vent. One setting is for fording. Turn it 90 degrees and it is for normal use. The fording setting closes the vent to prevent water entry. I have had two trucks that had the bar set for fording. They would run like you say, then draw a vacuum in the fuel tank and stop. If the tank is low on fuel, it will run longer than if the tank is full because there is more space it has to turn into a vacuum to stop the fuel supply.
If removing the cap solved the problem, turn the little bar 90 degrees and try again.
Regards Marti

I agree that the fuel cap position should be checked. I can't tell you how many people I have helped who thought they were vapor locked (well in a sense they were) while off roading in the Colorado Rockies. However, this is not usually a no start problem after sitting a while as the air will gradually bleed back into the tank. It for sure can cause the engine to run ratty after some gas is pumped out and the tank goes under a vacuum. I also agree that we are making this too hard. The OP's engine has enough compression to fire and run. Power may be down, but it should start. It has to be an ignition or gas problem.

 

[m3751]

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.

 

[scrapdaddy]

Dumb question, but are the sparkplugs wet from fuel after turning it over? Is fuel getting to the combustion chambers

 

[waayfast]

I agree with scrapdaddy-- have you tried a little gas down a spark plug hole or two or three ,replace plugs and try it?? Seems pretty far fetched but maybe-----

 

[Oldfart]

m3751
You have pretty well gone over the things to check. I am puzzled by your ability to rotate the distributor 180 degrees. The military distributor has an offset tang on the end that can only fit into the oil pump one way. ~~~ One other simple thing to check would be to take off the top half of the distributor and have someone engage the starter to see if the rotor is actually turning. ~~ I will see if I can find a picture or two of what I am talking about.

 

[m3751]

I’m not sure putting a small amount of fuel in a few calendars and trying it is going to work since the fuel need to be mixed with air to ignite, but it’s worth a try.

Regarding the distributor and the 180 degrees, it not the distributor that I’m rotating it’s the shaft that extends into the engine that rotates and activates the points (or the magnetic switch in my case). I had to change the entire igniter assembly out as no one could figure out this starting issue and it was suspected that the issue was with the entire assembly.

I may go ahead with a new fuel source temporality to absolutely eliminate the fuel issue.

 

[Oldfart]

m3751
I understand you are not rotating the distributor, but the distributor shaft. What I am talking about is the bottom end of that shaft. It has a tang that looks like an ordinary screwdriver that fits into the oil pump. That tang is not centered, but it is off set to one side. Even though you are using an aftermarket distributor (igniter) it should still have to index (fit) into the oil pump in order to spin. Because the tang is offset, it only allows the stock military distributor to be installed in one position. If the distributor you removed (to replace it with an electronic distributor) looked like the one described in Section 1 paragraphs125 through 130 of TM 9-8030 then it is a reasonable assumption the oil pump has the offset tang drive which means the distributor should not be able to rotate 180 out of time. ~~~ My earlier suggestion to check to see if the rotor was turning is a bit misleading. Clearly there is some rotational motion or you would not see spark at the spark plug electrode. What I was thinking is that perhaps the centered tang was just riding on top of the oil pump tang drive slot and there was enough friction to spin, but also slip that would not keep the distributor in time. ~~~ If your spark was anywhere near the right timing, there should have been some attempt at firing when you used ether. I really suspect you have a spark timing problem.

 

[scrapdaddy]

Somebody may have changed the oil pump out also. Civillian pumps have the slot in the middle, I believe. If the offset tang wasn't in it's slot, would he still be able to lock the dist. down? I think it's timing also, but this is a tough one.

 

[m3751]

Regarding the Electronic Ignition, this is a very small unit that fits into the existing distributor assembly and simply replaces the mechanical points with an electronic version, so the shaft of the distributor is original. The Electronic ignition is made by Pertronix and seems to be made to perfectly fit in the distributor of the M37. The part number is MV-161. It is specifically made for 24VDC applications and fits into the original 24VDC igniter housing like a glove. I used to have an issue with sluggish engine acceleration and replacing this completely eliminated that issue. So the shaft that comes out of the distributor that attaches to the oil pump is symmetrical and can installed 180 degrees out of phase.

 

[bubba_got_you]

[FONT=&quot]Well if it where me id pull the intake and check for blockages then verify that the valves are moving by pulling the valve covers. If that was all good I would spray starter fluid in each port and give it a shot if there is still nothing I would reinstall the intake and play with the timing just by retarding it and advancing it within 180*. [/FONT]

 

[m3751]

Regarding the timing - even if it's way off - shouldn't I get some indication the engine is trying to start. I don't get anything at all that makes me think that any of the fuel is igniting. When I try to start the engine the sound and feeling I get would be the same thing you'd get if you tried to sart the engine with the ignition in the "OFF" position.

 

[Oldfart]

Somebody may have changed the oil pump out also. Civillian pumps have the slot in the middle, I believe. If the offset tang wasn't in it's slot, would he still be able to lock the dist. down? I think it's timing also, but this is a tough one.

True about the civilian oil pump. I don't know what his aftermarket distribnutor uses for a block attachment.

There are a couple of pins along the distributor shaft and oil pump drive in the military set up. I don't know what the aftermarket distributor looks like, but if any of those pins sheared, the rotor might spin from shaft drag, but not stay in time.

This is a tough one. Hard to diagnose without having my hands on it.

 

[Oldfart]

Regarding the Electronic Ignition, this is a very small unit that fits into the existing distributor assembly and simply replaces the mechanical points with an electronic version, so the shaft of the distributor is original. The Electronic ignition is made by Pertronix and seems to be made to perfectly fit in the distributor of the M37. The part number is MV-161. It is specifically made for 24VDC applications and fits into the original 24VDC igniter housing like a glove. I used to have an issue with sluggish engine acceleration and replacing this completely eliminated that issue. So the shaft that comes out of the distributor that attaches to the oil pump is symmetrical and can installed 180 degrees out of phase.

Wow, I have never seen a Pertronix setup, but I have heard about them. Neat!! If the distributor shaft tang is symmetrical, then someone has modified it with a civilian lower shaft. ~~~ You are getting a spark and it sounds like sufficient spark to fire a fuel charge. You have introduced sufficient fuel in the form of ether to fire as well. The valves are in time (at least enough to move air through the engine as evidenced by suction at the carb and pressure out the exhaust. There is enough compression to fire a charge. ~~~ It sounds like the spark is not coming at the right time. This could be due to a 180 out condition since you have a symmetrical distributor drive or the spark plug wires are out of sequence. ~~~ It used to start so consider the changes since it last started.

 

[bubba_got_you]

Regarding the timing - even if it's way off - shouldn't I get some indication the engine is trying to start. I don't get anything at all that makes me think that any of the fuel is igniting. When I try to start the engine the sound and feeling I get would be the same thing you'd get if you tried to sart the engine with the ignition in the "OFF" position.

it depends on how far it is off. but id do what i said before playing with that