Need assistance to diagnose an MEP-831a engine issue

[hammick]

I picked up an 831a the other day. It had a major reset in'09 with a new engine. Has 15 hours. Initially it was making full power but was smoking at load more than I would like. Every once in a while it would pop and blow stuff out of the muffler. Like a dumb ass I kept running it.

It stopped making full power and would bog down at 2.7kw on the meter. I manually set the throttle to full power and it would run at 2.7kw but then the muffler caught on fire. Luckily I was able to get it shut down and put out the fire with a fire extinguisher.

I need to determine if this happened because it was heavily wetstacked or if I have a bad piston ring or something.

Should I start it up without a muffler or get it compression tested (or both)?

Thanks.

 

[tburk49760]

Ouch! No ideas. Someone here will have faced this before. Very curious.

 

[Chrispyny]

Honestly, i'm not a diesel mechanic, but i'm very mechanically inclinded.. My guess would be the ring was stuck, having sat for long. When you ran it, chances were it would unstick and free up, or snap and crack. It may have smoked at 2700 watts, and then just snapped or cracked. And now you may have cylinder scoring issues and need a new ring.

I'd look into what a gasket set for that engine costs. If not to pricey, tear it down and check the ring and cylinder. If the cylinder is ok but ring is bad, clean off the piston, replace ring, and slap it back together.

Prices for Gasket sets/parts for certain engines/pumps are sometimes rediculous. I purchased a slightly used Quincy QT-7.5 compressor at auction 3 years ago. I wanted to see the cylinder and see if there was any travel in the wrist pin to rod. The graphite gasket set was like $120. And it wasn't even a whole rebuild/overhaul gasket kit. Just the head gasket and a couple little things. I bit the bullet and got lucky as the pump was mint, as a replacement costs well over a grand! Good luck.

Of course, first get it compression tested!

 

[hammick]

If I start it up without a muffler and it runs fine with a full load can I conclude I just had a restricted muffler? I don't want to dump a bunch of money into this. I have a new muffler on the way but if the motor is bad I will probably just part it out. Nothing was damaged but the muffler and it was running strong when I shut it down and put out the fire.

Also does anyone know if the cheap diesel compression test kit from HF works on the Yanmar?

http://www.harborfreight.com/diesel-engine-compression-tester-20-pc-62594.html

 

[Guyfang]

Partner, remove the injector, and use a rubber adapter on the end of the tester hose. Stick it in the hole, hold it TIGHT and have someone else turn the engine over. The gauge should have a function to allow you to "capture" the reading on the meter. When done, let out the pressure and perhaps try it once or twice again. If the kit has an adapter to allow you to attach the tester directly to the engine, then use it. Its not rocket science. Read the directions and you will be good. And don't forget to read the TM. Lots of good info there. And yeah, if it runs fine without the muffler. Take a gander in the muffler and see if its plugged up. Just because the meter only had 15 hours on it, doesn't mean someone cleaned the muffler!

 

[hammick]

So I drilled a bunch of holes in the exhaust today to see what the insides looked like (removing the exhaust is a chore). No signs of any residue or wetstacking. The exhaust valve and exhaust port has heavy carbon buildup. The fire did not start inside the exhaust. It was the exhaust wrapper that caught on fire.

Here is my new theory. The genset wasn't making full power so I locked it into manual start/full throttle to troubleshoot. It was able to hold 2.7kw at full throttle. The unit overheated and didn't shut down because it was locked in manual start. The excess heat caused the fan behind the exhaust to fail. Temps increased and caused the exhaust wrap to catch fire.

So I will pull the valve cover and check the valves. I'll also do a compression test. If this isn't an easy to fix I will part it out.

 

[hammick]

Checked the valves. They were crazy loose. Spec is .10mm - .15mm

My exhaust took up to a .356mm feeler and intake up to .330mm feeler

I ran this engine for approx 2.5 to 3hrs like this. No telling how long the military did it.

The hour meter has 17.5 showing on the new engine.

A lot of time and expense on my hands to learn a good lesson. Always check the valves as part of the initial inspection.

I'm going to re-torque the head, put it back together and see if it runs properly.

 

[Guyfang]

I say once again, just cause the hour meter says 17.5 hours, does not mean the thing is in tip top condition. In any case, you are on the right track.

 

[hammick]

I say once again, just cause the hour meter says 17.5 hours, does not mean the thing is in tip top condition. In any case, you are on the right track.

Do you think running it with the valves that loose could damage the engine?I'm researching trying to figure out how loose intake and exhaust valves could have caused the exhaust blanket to catch fire.

 

[Guyfang]

Well, if the exhaust is to loose, and lets fire into the exhaust system, then things will get hot. I don't think that the valves will be damaged, if you didnt run it too long that way. Only way to find out is to take a look at them. If they are good, readjust them and fire it up.

 

[hammick]

Well, if the exhaust is to loose, and lets fire into the exhaust system, then things will get hot. I don't think that the valves will be damaged, if you didnt run it too long that way. Only way to find out is to take a look at them. If they are good, readjust them and fire it up.

Guyfang doesn't loose exhaust lash keep the exhaust valve closed longer? I thought tight exhaust valves cause excessive heat.

I'm trying to figure out why my genset caught fire. Maybe it's as simple as it was running overloaded because of crazy loose valve lash and I had it set to full throttle. Then the fan seized and that's all she wrote. I may have also had some diesel fuel on the exhaust blanket from cracking the injector when it was running.

Maybe I'll never know the cause.

 

[Guyfang]

Your right. My mistake. not thinking. I am looking at too many threads right now. I have never seen the blanket burn before. Maybe the preheater was stuck on? Or, maybe you're right about diesel on the blanket. I don't know, got to think about this some more. Interesting.

 

[hammick]

I put what's left of the muffler on and fired it up. Good news is it still makes power and the rear fan works. Bad news is it still has white smoke at idle and overloads and blows black smoke. However it makes more power as it doesn't overload until 3kw now.

I'll get it compression tested hopefully tomorrow.

I pulled the injector and it was pretty black with carbon. I took it apart and cleaned it up. After putting it back together it didn't spray. I bent the internal pins which caused the internal holes to be misaligned. Guessing they shouldn't be tightened too hard.

I have a new injector on the way.

 

[Guyfang]

Another problem that can cause white smoke is over filling the oil. On this engine, to check the oil, you do not screw in the oil dip stick. Just insert it in the hole, and pull it out to read it.

 

[hammick]

When I took the fuel injector apart yesterday and sprayed carb cleaner into the nozzle I was only getting two spray streams out of the nozzle. Looking at the Yanmar L70 service manual closer it says:

"the spray should be at the same angle (from all four injection ports) the spray should be smooth and steady without deviations (4 nozzles)"

I am hopeful the new injector I have on the way resolves my issues.

 

[hammick]

The service manual says that the engine is at TDC when the T mark on the flywheel lines up with the V mark on the head. Problem is the flywheel has two T marks. Does it matter which one? I've already adjusted the valves and put it back together so I can't measure the clearance at each mark unless I take it apart again.

The white smoke I am getting makes we wonder if I chose the wrong mark.

 

[Dewie38]

don't go by the engine service manual for setting timing
go by the tech manual for setting the timing because Yanmar changed the timing and max fuel setting for this application.

 

[hammick]

don't go by the engine service manual for setting timing
go by the tech manual for setting the timing because Yanmar changed the timing and max fuel setting for this application.

I used the military tech manual. Any idea why there are two "T" marks on the flywheel?