Bought another non-running 802a, begins to start, then falls off (Now a fix up thread)

[Digger556]

Hey all, I bought another non-running MEP-802a. It was robbed of many parts, so I've been going through it. I was told it ran and made power at one point, but engine quit starting one day. So far I've fixed the well nut, added the MOV, and dropped in some new batteries.

After changing fluids and all filters, I re-primed the fuel system and followed the TM to purge air from the injector lines. While cranking, the engine would pop a few times, but that was it. I checked the glow plugs and found the forward one was burnt out.

After replacing the glow plug, I stupidly neglected to double check the wiring on the other one and proceeded to burn up a second one because the rear glow plug was wired in a way that bypassed it and sent all 24 volts to the forward glow plug.

After replacing the forward glow plug again and rewiring both properly, things seem to be functioning better. At this point I cycled the plugs for 30 sec and cranked the engine again. It starts to fire and pick up rpm, but after a second or two, it falls on its face and quits popping, just blowing smoke.


I'm looking for what to check next. Should I be pulling the IPs or injectors to disassemble and clean them?

 

[DieselAddict]

Have you checked that the fuel system is fully primed and you have fuel flowing back to the tank?

 

[Digger556]

Have you checked that the fuel system is fully primed and you have fuel flowing back to the tank?

The fuel system is primed and I'm getting squirts when I crack the line nuts at the injectors. I followed the TM, opening the lines at the IPs first and loosening the IP nuts, then the injectors nuts.

I have not checked the fuel return to the tank yet.

 

[Ray70]

Are you working on it in the cold or warm garage?
When you start cranking it, keep an eye on the oil pressure.
If it sounds like it's about to start but then seems to loose compression and the oil pressure is pegging up over 80 Psi your pressure relief valve may be stuck shut and your lifters are pumping up solid and hanging your valves open.

 

[Digger556]

Are you working on it in the cold or warm garage?
When you start cranking it, keep an eye on the oil pressure.
If it sounds like it's about to start but then seems to loose compression and the oil pressure is pegging up over 80 Psi your pressure relief valve may be stuck shut and your lifters are pumping up solid and hanging your valves open.

It's been in the garage. Outside air temp has been 40°F

That's an interesting thought! The oil pressure gauge doesn't work, so I'll rig up something manual.

I had a little more success tonight. Through several starting attempts, the engine would run progressively longer each time. One attempt got so close, I released the starter and it chugged for 1 or 2 seconds on its own. I re-purged the fuel lines, but no change. (They seemed like there was no air anyway). Thinking the IPs or injectors might be sticky, I warmed them carefull with a small torch. No change.

I noticed when its firing, it blows solid black, but when it falls off, it starts blowing light grey smoke from, what I think, was the rear cylinder. I say rear because I have the muffler off and the white smoke comes out of the exhaust hole and the rear mounting bolt hole, but not the front one.

Here is a quick video.

 

[Ray70]

Well, that grayish smoke is most likely also an indication of low compression in that cylinder.
Given the amount of time it takes to start puffing gray I definitely thing the oil pressure is the next thing to check.
Stick a gage with a 1/8" NPT thread into the fitting near the dead crank switch and watch it while attempting to start it.
anything much over 40 -50 PSI indicates an issue, but typically a stuck relief valve will shoot up to 80 PSI or more in just a few seconds.

 

[loosegravel]

Are you working on it in the cold or warm garage?
When you start cranking it, keep an eye on the oil pressure.
If it sounds like it's about to start but then seems to loose compression and the oil pressure is pegging up over 80 Psi your pressure relief valve may be stuck shut and your lifters are pumping up solid and hanging your valves open.

Unfortunately, if the lifters were pumping up solid, the valves would be hitting the piston crowns. Just speaking from experience here.

 

[loosegravel]

It may be another case of piston ring seizure. I had an 804A unit this past with low compression. When I tore this engine down, I had 3 out of 4 pistons with ring seizure, the piston crowns were literally wiping themselves off on the cylinder walls. I was able to get the 3 pistons, rings etc. to get it running again. But I never found the culprit. I chalked it up to "extreme wet stacking/carbon build up."

 

[loosegravel]

I believe the 802A and 803A units use the same internal engine parts. https://www.steelsoldiers.com/threads/dn4m-pistons.208238/

 

[Ray70]

Yes, it could be rings, and a bunch of other things, but I have had more than 1 machine with a bad oil pressure relief valve.
Especially when the oil is cold and thick the pressure goes too high and the lifters pump up, hanging a valve open, loosing compression and then puffing gray smoke.
As soon as the valves no longer seat the engine usually quits trying to start and the lifters don't quite pump up solid, often preventing the valves from touching the piston. Luckily if they do make slight contact the piston tops are flat and the valve don't get bent, the lifter will give way a tad, but you can easily end up with bent pushrods.
Oil pressure is the simplest and an important thing to check first... once he has a working gage.
If that check out fine, next thing is to check compression.

 

[Guyfang]

If its the valve, and you can get the set running, we would fill the engine up with ATF and run it a while. That always corrected the problem, when we had low oil press due to the valve. But first you need to get it to run. The picture shows a set that doesn't look like its been run through the ringer. Mostly we saw stuck valves from sets coming back from down range. But do check it. Its simple and easy.

 

[loosegravel]

Yes, it could be rings, and a bunch of other things, but I have had more than 1 machine with a bad oil pressure relief valve.
Especially when the oil is cold and thick the pressure goes too high and the lifters pump up, hanging a valve open, loosing compression and then puffing gray smoke.
As soon as the valves no longer seat the engine usually quits trying to start and the lifters don't quite pump up solid, often preventing the valves from touching the piston. Luckily if they do make slight contact the piston tops are flat and the valve don't get bent, the lifter will give way a tad, but you can easily end up with bent pushrods.
Oil pressure is the simplest and an important thing to check first... once he has a working gage.
If that check out fine, next thing is to check compression.

Got it. I always try to be respectful of others educated opinions On the topic of seized piston rings, this was mentioned as the cause of piston failure on the DN4M engine that I was working on last year. Nobody ever said what the possible cause of piston ring seizures on these engines is?

 

[Guyfang]

Sitting in parking lots, for years on end, not being started is a good place to start looking for a cause.

 

[loosegravel]

Sitting in parking lots, for years on end, not being started is a good place to start looking for a cause.

This is true!

 

[jamawieb]

I agree with Ray70 its low compression. When this happens, i usually use the dead crank and pull the dipstick. If it is compression, a large amount of pressure and oil will come out of the dipstick location. Usually you will have a small amount of pressure with the 802a but not alot.

 

[Guyfang]

Its supposed to be a vacuum. Not pressure. You get some oil spitting out. But suposed to be a vacuum.

 

[Digger556]

Are you working on it in the cold or warm garage?
When you start cranking it, keep an eye on the oil pressure.
If it sounds like it's about to start but then seems to loose compression and the oil pressure is pegging up over 80 Psi your pressure relief valve may be stuck shut and your lifters are pumping up solid and hanging your valves open.

Ray, you nailed it. Holy moly that's a lot of pressure!

 

[Ray70]

Well, good to know we've found the problem! Now you need to take the side cover off the motor and unscrew the pressure relief valve tube that screws into the back of the oil pump, next to the pickup tube. Item #1 in the TM image.
Take it apart and clean it good! It has a spring loaded check ball in the end after you remove the snap ring.

 

[loosegravel]

Well, good to know we've found the problem! Now you need to take the side cover off the motor and unscrew the pressure relief valve tube that screws into the back of the oil pump, next to the pickup tube. Item #1 in the TM image.
Take it apart and clean it good! It has a spring loaded check ball in the end after you remove the snap ring.

View attachment 888684

Ray! Great job on this my friend! You're obviously speaking from experience on this too. I had no idea that the oil pressure relief valve being stuck could cause the lifters to pump up, causing the valves to not close all of the way, thus a no compression situation. I definitely learned a bunch here. Thank you

 

[Ray70]

Thank you! Glad to help and glad to share my experiences, and yes.... been there and seen that! I've had at least 2 with the same issue, one was a pretty new, low hour machine... super clean. Ran fine in the warm weather, ( probably just barely got by with warmer oil ) but if temp was below 20F the oil was thicker and it would do the same thing, but like 80-100 PSI, not 240!
Crankcase was clean inside and relief valve looked good, but it would stick closed at times.
I have a feeling mine was stuck partially open and Digger's is completely frozen shut.