Problems with engine

[Roger Friedrich]

I'm trying to figure out what would cause my engine in my M37 not to run. I have checked the compression but I was told I need to have the engine at running temperature to get a correct compression reading. Currently the readings for each cylinder is 30 psi or lower.

I then started to wondering about checking the valves to see if they were out of adjustment but again the Army manual I have states the engine needs to be at operating temperature. My question is can I adjust the valves cold and what would the thickness I would use on the feeler gauge?


Thanks for any help,


Roger

 

[whatadeuce]

Roger, Did you ever see this engine run? Is it the original 6 cylinder ? If it did run since you own it, did you do any work on it, and what work did you do?

 

[NDT]

30 PSI is way to low. Either the engine's valves are massively misadjusted, or they are corroded under the seats.

 

[Roger Friedrich]

Guys

I have had the M for several years and have drove it in parades. I the engine is original and the only thing I've done to it is a tune up. I drove it down the county road and back but as I was turning into the subdivision the engine started to act up.
I checked the plugs which were blacken replacing them with Champions J8 also I replaced the fuel pump adding an clear inline filter.

I was able to drive the M almost to the parade starting point when it starting backfiring and lost of power. I let it set till after the parade when my son-in-law replaced the plugs again drained the float bowl on the carb and removed the float needle to see if something had got jammed in the needle area.

I got the M home and started to figure things out. I removed the distributor checking the points after I put the distributor cranking it over getting a blue spark. Pulling a plug cranking it over the spark at the plug was yellow. I don't know how old the plug wires are they came with the truck.

I was wondering if the valves could be checked cold. I also been told the compression should have been check at normal operating temperature which it wasn't

Any suggestion would be appreciated

Roger

 

[NDT]

Sounds like the famous M37 vapor lock. Or flooding due to stuck needle. To eliminate these, run a rubber hose from pump to carb and put a inline filter right before the carb. Route the hose away from the manifold.

 

[Roger Friedrich]

The fuel lines are rubber and run to the inner fender with a inline filter. The problem existed with the old fuel pump as well as the rebuilt original.

My friend suggested to check the needle which I did and found nothing

 

[whatadeuce]

When you did the tune up, did you set the dwell? And if so, did you tighten the distributor adjusting fastener back tight, so that it did not drift? Check you timing once again

 

[Roller]

Compression is your problem, 30 is way too low, 90 should be the minimum and being hot is not going to make up the difference. If the engine was running before the odds of all six losing compression at once is strange. Valve clearance can be set cold, add .002 for the exhaust but set the intake as normal.

Frank

 

[T. Highway]

I have to agree with ROLLER, the compression is way too low. I have seen valves sticking before and resulting in not fully closing / seating.
This will cause both the misfire and low compression. Time to pull the head and check it out.

Bert

 

[KaiserM109]

Other than driving the **** out of 2 M37s in the Army and a Tucker Sno Cat my dad had with the same engine, I'm not familiar with fixing problems on the engine. Flat heads I am familiar with, the Hurricane Six, often had timing chain problems. If you are going to all the trouble of pulling the head, take a serious look at the timing chain and gears. CAUTION: Make sure you know how to time the gears. It wasn't so easy on the Hurricane Six, even with the manual. It wasn't anything like V8s I've worked on; you had to point the markers sideways and count the links between them.

 

[Roger Friedrich]

Thanks for all the help but I think it's a new engine for my Christmas present haha

 

[T. Highway]

Honestly you could have the head removed and take a look at the valves in under one hour. No need to mess with the timing chain cover at this point.

Bert

 

[just me]

****, if I was closer I'd take your old one from you. (Could have it rebuilt and in my truck in under a week.) I suggest trying the compression test again using a screw in tester, not one of those rubber tip hold 'em things. Remove all six plugs, pull hand throttle out all the way and leave it there. Choke off. Crank it and watch the needle. It should jump to around 70 or so on the first revolution and then pump up to 90-120 by 3 revs. (A new engine will get there on the first turn, on old worn one will take a little more.) Do this to all cylinders and record the readings.
Now, pour a tablespoon of oil into a cylinder. Run the test again. If it jumps to compression much more quickly, rings are worn. If there is little to no change, valves are suspect.
Easy peasy. Do it cold or hot. Takes about 5 minutes.
If you can get your paws on a leakdown tester, it will tell you a lot more about internal conditions.

 

[NovacaineFix]

I suspect the valves as well, 30 psi is way too low, even for a worn out motor, but you stated that this is new. The thing that keys me in is the backfire.

I would do like user just me suggested, to determine the compression. You can set these cold, they had to from the factory at one point, right? About .002 more like Roller suggested should get you fairly close.
Many things could have happened, a bent valve, stuck valve, a worn cam lobe, something stuck in the valve seat, hopefully none of these, hopefully just adjustment issues.

If you have a type of compression tester that you can connect an air line to you can also do the following test using regulated air.

1. Turn the engine over by hand so that the valves for the suspect cylinder are both closed, should be on the flat of the cam lobe.
2. Screw in the tester in the suspect cylinder, apply regulated air to the cylinder (not the full 150 psi)
3. Listen to hear where any air is escaping that will tell you what valve, if not both are in need of inspection or adjustment.
- of you loosen both valve adjustments and still hear air you may have a bent or broken valve or something stuck between the valve seat carbon, part of a spark plug, etc.\
4. No air heard, adjust your valves to the specified adjustment and move on to the next cylinder.

Hopefully from the backfire, it did not cause sever damage or blow a head gasket, during all this, if you do it, always look for any fluid seepage or bubbles coming from the radiator.

 

[whatadeuce]

This is such a helpful thread...Thank You...I wish I knew how to post a remark as I see others due ...,

 

[Roger Friedrich]

Well the engine is out of the M37 and apart. The timing is one tooth off so it's part of the problem. As I took apart the engine it appears to have been overhauled but not by the military since there is no rebuild tag on the block. When I pulled on one of the pistons to see what the rings looked like and if they were stuck the rings weren't stuck, but the wall of the cylinder was shiny so that added to the low compression also. This week its going to the machine shop were there is a guy who works on old engines like the 230 flat head.

Thanks everyone for the information

 

[dmetalmiki]

When you get it back in be sure to check the distributor, particularly the Condenser. as that sounds as if it might have gone out you whilst driving to that event. (don't spoil the ship for a 1/2 penneth of tar!).