MEP 831 FAQ for owners or potential buyers

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paraclete comes

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Just wanted to post up a few facts that might help those out looking for an MEP 831a 3kw diesel generator or already own one. This will get updated as I find more information so please be patient with me.


DRS Fermont's 3kW Tactical Quiet Generator Set is the first Generator Set produced for the US Military with a Permanent Magnet Generator (PMG) and variable speed technologies to pass rigorous Government qualification testing.
Power output3kW @ .8 power factor
Voltage120, two wire; 120/240, three wire
EngineYanmar Diesel, L70, Air cooled, manual & electric start MORE SPECIFIC the Yanmar L70AE-DE-
GeneratorDRS PMG
Sound level69 db at full load
Fuel tank capacity8 hour tank
TestsMIL-STD-705 and MIL-STD-810
FuelJP-8, DF-2, DL-2
Mechanical
Dimensions
(LxWxH inches)34.5 x 27.9 x 26.5
Weight
(Dry without battery)270 lbs

This generator runs the following consumables:

Factory Battery- concorde RG-24-15A1 (please note however this battery is only sold to the government and although you can obtain this on the surplus market the civilian equivalent is readily available)

Commercially available Battery- concorde RG-24-15 (note this battery is identical in size and performance to the A1 battery specified by the military. The only difference is it is certified for aircraft and has #8 metric terminals instead of standard auto clamp on type terminals. You can easily convert your mep831a terminals to fit this battery. You will need two 5/16" ring terminals to convert this. Once you have those simply remove the automotive clamps and install these ring terminals and your in business.

Air filter- yanmar 114250-12580

Oil filter- yanmar 114250-35110

In line fuel filter- hastings gf-27

Main fuel filter w/water separator- wix 33583

Glow plug-

Oil- 10w30 ( Oil should be changed every 100 hours and it takes a little over 1 gallon)

Fuel- jp8 or diesel (*note* if you run diesel occasionally add a lubricant such as opti-lube or Lucas or any other commercially available diesel lube. The epa has mandated removal of lubricants and it's hard on your injection pump. Also if you live in northern climates like me remember to use #1 diesel or at least a 50/50 blend in winter. That will lower the pour temp on your fuel and help prevent clogs in lines or filters.

As I get more information on this stuff I will update it. Also a big thanks to the guys that helped contribute the info to this.

Here's the TM for the MEP 831

http://greenmountaingenerators.com/wp-content/uploads/2012/09/MEP-831A-OPERATOR-UNIT-AND-DIRECT-SUPPORT-MAINTENANCE-MANUAL-INCLUDING-REPAIR-PARTS-AND-SPECIAL-TOOLS-LIST-TM-9-6115-639-13P.pdf
 
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Cord

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The engine is specifically a Yanmar L70AE-DE. It'll take 10w30 oil. Personally, I've been particular to the Shell Rotella product. Per Yanmar, oil change interval is every 100 hours and it'll take just a little over 1 quart. Checking the oil level is a bit different from what we might be used to; with the unit level, fill the oil until it's level with the mouth of the filler port (per the TM 2 threads below, but that's really splitting hairs). The dipstick only reads amounts that are less than full. To read the dipstick don't thread it in, just rest it in the opening. The filter really isn't changed all that often. It's more of a screen that's screwed into the engine than a filter.

If you are starting in cold weather (or are lazy and just want the engine to start on the first pull) remove the rubber plug on top of the engine and put several drops of engine oil in the hole. It's some sort of starting aid it works freekin' awesome!
 

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Cord

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That sounds about right. It has a square black rubber plug. Remove the plug and you'll have a round hole with a small black hole in the bottom. I've tried tipping a little oil in from a quart bottle and usually make a mess of it so I've switched to using an oil can. The amount of oil doesn't appear to be critical. With the oil can I give it one shot, with the bottle I'll over fill it. Starts just as well either way. Oil viscosity doesn't seem to be critical either. I've been using cheap farm grade 30w.
 

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Cord

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Here's a question for others: reading through the TM, I'm wondering if a battery is required for operation when the set is manually started?

1. The manual references the direct current system "provides generator control circuitry, relay logic, and engine cranking".
2. Under "battery" section it says "If battery is not installed, battery cable ends must be isolated from each other, and positive end must be isolated from ground. Failure to isolate battery cable ends could result in severe electrical discharge. When not connected to battery, connect battery cable ends to plastic storage stud."
3. Under manual starting it says "Note: If generator has an operational battery installed, it will be necessary to reset the LOW OIL PRESSURE (10) fault on the malfunction indicator module..."

I haven't seen anything in the manual disallowing usage without a battery.
 

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R Racing

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I would say yes you could run it without a battery and insulate the + lead. On a second note whats the thin red wire laying on the battery ? I have seen them on several units laying loose in the cabinet ?
 

Cord

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Connection for the solar battery maintainer. The chargers appear to be field installed, hence the sloppy wiring and crimp connectors.
 

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Cord

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Well, this is what I get for being an internet expert when I haven't touched the gen set. I know the Yanmar engines as I currently own two of the air cooled ones. Both of these have the oil starting assist. I see that for what ever reason, the hole is plugged on the generator. Oh, it's still there, but it's plugged from the factory. Living in Wisconsin, I know that I'll want this feature so I'll try to add it. If successful, I'll post some pics of the process. There are pics in the attachment below.
 

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Cord

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It's nearly impossible to get a picture of the engine serial number because it's under the muffler. Because I have my engine torn apart, I was barely able to get a pic of the plate. To order any parts from a Yanmar dealer, you'll need the model and serial number.
 

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Dewie38

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Early production Mep831's had a Yanmar made in Japan later they went to Italy for production.
The earlier ones had black plugs in the valve cover that were cut off and the plug was glued into the cover.
Yes the sets will run without the battery it should run off the battery charger.
No need to read the dip stick, look into the hole and the oil should be up to the bottom of the threads where the dip stick threads in.
The engine doesn't hold a little over a gallon of oil it holds a little under a quart.
 

cdre

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All of the 831a's I bought came with a piece of what looks like radiator hose in there - about 3 or 4 inches long. Loose and usually on the right side inside of the case. Anyone know what that is for? Also, what's the little shelf on the right side with the tie down strap for?
 

DieselAddict

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The little radiator hose looking thing goes on the intake of the engine. You can see if it looks like this one in the photo behind the fuel filter.

20150130_171542a.jpg

Can you take a photo of the shelf on the right? I don't seem to have that on mine.
 
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cdre

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Got it. All of mine were sealed up with aluminum tape, so the hoses were removed. I'll snap a pic today.
 

Cord

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So, whomever tried to work on my engine attempted to remove the oil filter without removing the retaining bolt. Doesn't surprise me because they made a mess of everything else they touched. When they did this they jacked up the oil filter so I decided to replace it. I didn't realize the replacement filter did not include the o-ring so I reused the old one until I could get a replacement. When I tried to start the engine it had no oil pressure. I confirmed this by removing the oil pressure sending unit and confirmed there was no oil flow. I called up Yanmar and they had no ideas why I wouldn't have pressure because the pump is driven right off the govenor. To access the oil pump I had to pull the enitire generator head apart. I'm happy to report that this isn't terribly difficult.

The trick is that you CAN NOT remove the stator (the outer part) first. You must pull the armature first and then remove the stator. The armature magnets are so strong that it's litterally impossible to remove the stator. The moment you get it close to coming off a prybar will slip and the stator will magically reinstall it's self. The better way is to use a two jaw steering wheel puller and two 1/4"x2" grade 8 bolts. Thread the bolts in until they bottom out. I then used a 1/4" socket as a spacer to protect the bolt hole threads. It takes a fair amount of force to get the armature to break free, hence the grade 8 bolts. Even after the stator breaks free, you still have to keep turning the puller to extract the armature. Yes, the magnets are so strong you need to use the puller to remove the armature. Once the armature is out you can remove the stator retaining ring and the stator comes right off. Super easy. There is just enough wire length to lay the stator on top of the batteries. Just put something over the batteries so you don't short them out. I used a piece of packing foam for this.

Now I had access to the oil pump. I tore the pump apart and couldn't find anything wrong with it. Totally stumped I decided to pull the oil filter and replace the o-ring before I turned in for the night. I noticed the original ring was very loose on the filter and had gotten pinched. I put the new ring on and had to tap on the filter to get it to fully seat. You really have to remove the electronic throttle control to see this. The throttle is only held on by two bolts and has a disconnect for the wiring so there is no reason to not remove it. By now I was totally stumped as to why the engine didn't have oil pressure. Desperate, I tried to start the engine again and got pressure! The problem must have been the pinched o-ring. I'm posting this as a warning for anybody who may be tempted to replace the oil filter. Plan on replacing the o-ring and make sure the filter is fully seated without pinching the o-ring.
 
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Dewie38

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Very strong magnets, Samarium cobalt, rare earth magnets.
Have you attempted to re-assemble the PMA?
When you go to put the rotor back inside the stator the magnets will pull it in and it will hit on one side.
What you need to do is put a thin piece of plastic (mylar) inside the stator before you re-install the rotor. (Mylar like a drum head)
Using the wheel puller to hold the rotor as you insert it into the stator
Bolt the rotor back on to the engine shaft then pull out the plastic.
If you don't do this the rotor will rub.
When you finish bolting the stator and rotor you can push down and hold the decompression lever and rotate the engine by hand by pulling the rope start, the engine should turn over nice and easy.
As far as the oil filter goes: there is suction at the filter and with a pinched o ring you cavitate the pump.
When you re-install the filter line the holes up in the engine and filter, wiggle the filter back and forth while pushing the filter in, do not rotate the filter fully just back and forth, it should go in nice and easy.
Those are washable filters they do not need to be replaced
 

DieselAddict

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I have some thin plastic cutting boards I was thinking about using. They may be a little thicker than a drum head. How much gap do you think there is between the stator and rotor?
 
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