MEP-003A oil pump seized out of the blue

msim · Nov 26, 2018

My MEP-003A had been running fine and suddenly shut down from a seized oil pump. The drive gear shed a few teeth and then the pump shaft sheared off at the pump. Is this normal?

I can't think of any reasons, It gets proper oil changes and Wix spin on filters and had the last about 10 hrs ago. The guage read it's normal high cold reading of the needle all the way to the right and dropped down to the usual midway reading once warmed which seems to not take too long. I had just checked the level and topped it off to the full mark before poking the acetylene 'starting' torch into the intake and it fired right up. It was about 45-50°F out, it ran about 30-60 mins when it abruptly stopped.

DieselAddict · Nov 26, 2018

Definitely not normal.

What does the pump look like internally? Any scoring?

Post some photos of the damage if you can.

msim · Nov 26, 2018

DieselAddict said:
Definitely not normal.

What does the pump look like internally? Any scoring?

Post some photos of the damage if you can.

I'll take pics but I don't have it out yet. The front of the engine is apart and pump loose but wont come out. It appears the oil pan has to come off and that also holds the motor mounts so I have to levitate the whole engine.
There's nothing in the MEP or Onan manuals I can find about that, only the the oil base(pan) must be removed.

Chainbreaker · Nov 26, 2018

Any idea how many hours are on the unit? Is this an original hrs unit or has it ever been rebuilt (Reset tag?). Good thing it abruptly stopped (low oil pressure cut-out switch did it's job) before it completely seized the engine.

When you drained the oil did you by chance filter the oil through a fine strainer? Might want to check to see if any other objects were in the oil, other than oil pump parts.

Acetelyne torch start start? Were your glow plugs not working properly? It really shouldn't need any other starting assistance at that temperature range besides holding it in "Preheat" setting for 60 seconds.

Guyfang · Nov 26, 2018

How old are you? In all probability the oil pump is considerably older then you. I have only seen one 002 or 003A oil pump go bad. Normally I would consider it one of the most reliable parts of the engine. But like people, with age, you got to expect that something can go wrong.

If you are using a torch to start this set in 45-50 degree weather, you might want to read up on preheat and glow plugs in the forum here.

msim · Nov 26, 2018

Chainbreaker said:
Any idea how many hours are on the unit? Is this an original hrs unit or has it ever been rebuilt (Reset tag?). Good thing it abruptly stopped (low oil pressure cut-out switch did it's job) before it completely seized the engine.

1100 hours. It's from 1986 and came to me last year through a buyer of govt auctions. It's weathered but everything worked (that would soon change), it didn't leak oil(!)

I don't think the oil pressure had a chance to drop, it seized up with the teeth from the oil pump gear sheared off and jamming the crank gear. It was 1-2 seconds time for it to decelerate to a stop and i couldn't rotate the crank until I got some sheared teeth out. Almost all the oil pump gear teeth are sheared off and the shaft was sheared at the oil pump.

Using the torch was mostly a matter of a battery nearing it's end after a while of the charging system not working well, (fixed by tightening screw terminals around the regulator). It cranked slower with little crank time available when I started using the torch out of desperation and it was handy. My glow plugs are also bad. This isn't a hobby machine, I desperately need it for my livelihood and need it to start.
I was really surprised how well the torch worked. I use a small brazing tip and flame set like it was going to do some light welding but with a bit more acetylene than O2. I place the flame in the intake just as cranking begins and it always starts immediately. I've seen folks start diesels with a big yellow flame that looks like a campfire going into the engine but mine is a fairly small blue flame. I can't believe it works, or used to work. I guess I need to start using past tense with this POS.

msim · Nov 26, 2018

Guyfang said:
How old are you? In all probability the oil pump is considerably older then you. I have only seen one 002 or 003A oil pump go bad. Normally I would consider it one of the most reliable parts of the engine. But like people, with age, you got to expect that something can go wrong.

If you are using a torch to start this set in 45-50 degree weather, you might want to read up on preheat and glow plugs in the forum here.

I'm no spring chicken. In fact I existed before this clump of ungrateful scrap by a good score or two, I forget if a score is 10 or 20, my memory aint what it used to be.

Even if the oil pump were ancient and worn out, a failure mode of seizing should be near impossible unless a big chunk of metal winds up in the pump. Do you know any details about the one or two other oil pump failures?

I've had some bizzare problems. Several months ago it had a grounding issue from corrosion at the points at the front as others have had. This was also the path for starter current which I don't understand when the negative battery cable terminates where the starter is, So all the current had to find a new path. With all the metal stuff bolted together to create a MEP there must be many possible paths, but guess where the best path for current to flow from front to back was on mine?....Through the accelerator cable, it burned in two from the current about midway. I don't know what role the main generator might have or not, the main output power has been without any problems I know of, I'd love to hear from someone knowledgeable on why a grounding issue leads to a burned up-by-high-current throttle cable.

Since high current can somehow wind up flowing through something as unlikely as a throttle cable, would oil pump gears also be possible?. I feel silly for tossing that out there but the oil pump is on the path to the throttle cable

leedawg · Nov 27, 2018

msim said:
1100 hours. It's from 1986 and came to me last year through a buyer of govt auctions. It's weathered but everything worked (that would soon change), it didn't leak oil(!)

I don't think the oil pressure had a chance to drop, it seized up with the teeth from the oil pump gear sheared off and jamming the crank gear. It was 1-2 seconds time for it to decelerate to a stop and i couldn't rotate the crank until I got some sheared teeth out. Almost all the oil pump gear teeth are sheared off and the shaft was sheared at the oil pump.

Using the torch was mostly a matter of a battery nearing it's end after a while of the charging system not working well, (fixed by tightening screw terminals around the regulator). It cranked slower with little crank time available when I started using the torch out of desperation and it was handy. My glow plugs are also bad. This isn't a hobby machine, I desperately need it for my livelihood and need it to start.
I was really surprised how well the torch worked. I use a small brazing tip and flame set like it was going to do some light welding but with a bit more acetylene than O2. I place the flame in the intake just as cranking begins and it always starts immediately. I've seen folks start diesels with a big yellow flame that looks like a campfire going into the engine but mine is a fairly small blue flame. I can't believe it works, or used to work. I guess I need to start using past tense with this POS.

I have a mep 003a and its anything but a POS Its the set I have had the longest (past 18 years). Last year it powered my house for 7 days straight, during the California wildfires 167 hours running around the clock to keep well-pumping water to spary down our yard and house. Burned through 3 barrels of diesel without missing a beat. I doubt you will find any other non military set that is capable of doing this at anywhere near the price you paid for your 003a. Sounds as though possibly the unit you have has been a bit neglected and needs some going through. You talk about grounding issues and a lot of weathering all signs perhaps its lived a hard life. That being said id never expect the oil pump to instantly fail.

If I was you id just simply go to this site here is a link and purchase this rebuilt motor for 800 bucks and just swap it in and be done with the problem.
https://www.ebay.com/i/222894682952?chn=ps

msim said:
I'm no spring chicken. In fact I existed before this clump of ungrateful scrap by a good score or two, I forget if a score is 10 or 20, my memory aint what it used to be.

Even if the oil pump were ancient and worn out, a failure mode of seizing should be near impossible unless a big chunk of metal winds up in the pump. Do you know any details about the one or two other oil pump failures?

I've had some bizzare problems. Several months ago it had a grounding issue from corrosion at the points at the front as others have had. This was also the path for starter current which I don't understand when the negative battery cable terminates where the starter is, So all the current had to find a new path. With all the metal stuff bolted together to create a MEP there must be many possible paths, but guess where the best path for current to flow from front to back was on mine?....Through the accelerator cable, it burned in two from the current about midway. I don't know what role the main generator might have or not, the main output power has been without any problems I know of, I'd love to hear from someone knowledgeable on why a grounding issue leads to a burned up-by-high-current throttle cable.

Since high current can somehow wind up flowing through something as unlikely as a throttle cable, would oil pump gears also be possible?. I feel silly for tossing that out there but the oil pump is on the path to the throttle cable

How do you know high current severed your throttle cable? Does it look like an arc welder struck up where the cable is severed? Are you sure the sheath of the cable did not rub away on something or even worse rub through one of the main gen leads? There is a huge grounding braided strap that runs from the bell housing where the starter is to the battery perhaps you need to take this off and clean everything up from the corrosion. You did mention it was very weathered. Sounds like you will have to do this anyway based on the condition of the motor now anyway being that its going to be a partial rebuild or simply a motor swap. Again my .02 you cant rebuild that motor for less than the auction mentioned above especially if you factor your time in.

Also how are you getting a flame into the intake, with the air intake filter and hoses in place? Or did you take this off to do that if so what kind of air filtration is happening when the motor is running? Again sounds as though the set has a lot of neglected maint should just be able to preheat and fire it up that is how mine is, ive never had to so much as give it a squirt of ether just starts.

And to answer your question about the oil pump burning up from current flowing through im going to say no. It would take an incredible amount of current to do that and for a sustained period of time to burn up those parts just don't see that happening. That being said two 12 volt batteries do have enough current to weld with, ive done it while 4 wheeling and broke a suspension bracket. But they don't hold out long when you put them under that kind of load and there is no way the alternator puts out that kind of current. I think you just had a fluk failure of the oil pump you could attempt to replace it and see how she goes but as I said before the time and trouble think id just replace the whole motor knowing I am solving multiple problems with one stone.

Good luck!!! and I am sorry to hear about the troubles.

Mr4btTahoe · Nov 27, 2018

Oddly... greenmountaingenerators has a page showing the same failure that they warrantied on one of their units. Found it the other day while doing some digging for info on my 003a.

https://greenmountaingenerators.com...n-oil-pump-mep003a-benefits-warranty-program/

I would think for the teeth to fail like that, something would have had to get lodged in the gear or inside the pump itself. If the pump slowly seized, the engine would have likely stalled out instead of locking.

Chainbreaker · Nov 27, 2018

msim said:
1100 hours. It's from 1986 and came to me last year through a buyer of govt auctions. It's weathered but everything worked (that would soon change), it didn't leak oil(!)

I don't think the oil pressure had a chance to drop, it seized up with the teeth from the oil pump gear sheared off and jamming the crank gear. It was 1-2 seconds time for it to decelerate to a stop and i couldn't rotate the crank until I got some sheared teeth out. Almost all the oil pump gear teeth are sheared off and the shaft was sheared at the oil pump.

As long as the 1100 hours you reported are original your '86 unit has VERY low hours. I have an '86 -002 with 1761 hrs and I consider it to be very low considering its going on 32 yrs. However, my unit has lived its entire life on the M116a trailer with its cover, so I don't have any of the weathering or corrosion problems that you have observed on your unit. My '86 unit runs like a top...as good as or better than my 91 unit with just 782 hrs.

You unit may have stopped suddenly due to the oil pump seizing but you really don't know if there were any foreign objects circulating in the oil beforehand that may have led to your oil pumps eventual sudden demise. Could have potentially done other damage to engine internals over time. If this unit is tied to your livelihood, I would seriously consider Leedawgs suggestion and look into purchasing and swapping in a rebuilt engine. That way you have a fresh engine as well as new glow plugs and the charging system should be up to snuff as well.

Then when you have your unit sorted out and up and running you can take your time to go through your old engine and repair it or use it as a potential parts donor. Injection pump, injectors, sensors, starter, etc. should all be good parts, any internal would need close inspection to determine if undamaged.

rustystud · Nov 28, 2018

The oil pump shaft and gears are hardened, so I expect you will find some foreign piece of garbage in that pump once you tear it down. I have never seen any vehicle or stationary engines oil pump break without it being caused by some external force.
Worn out, yes. Broken up, no.

Guyfang · Nov 28, 2018

Roger that! Don't just try and replace the pump. Take a real good look inside for "spare" odds and ends that may be floating around.

msim · Nov 30, 2018

Some pics

The oil pan and closeup show random debris. Each of those specks is different, paint chip, crud, aluminum shaving, brass... Nothing scary among them like chunks of steel.
The screen strainer is intact, anything going in passes thru it. I cleaned the oil pump parts, other pics are as they were. The oil pan was propped up at an odd angle for an hour or 2 to let oil escape
When I drained the oil, I wrapped filter paper around the oil drain tube, it collected no debris.
The pic up into the crankcase is not to highlight anything except the cleanliness state.

msim · Nov 30, 2018

rustystud said:
The oil pump shaft and gears are hardened, so I expect you will find some foreign piece of garbage in that pump once you tear it down. I have never seen any vehicle or stationary engines oil pump break without it being caused by some external force.
Worn out, yes. Broken up, no.

I've seen close tolerance 'elipse internal gear' pumps jammed from debris and expected to see one here but it's a fairly debris tolerant spur gear pump. This is the first I've seen one seized.
To make it interesting, I can't find any trace of a chunk or any signs on the internal sufaces. It looks like a pump in great shape aside from the shadt being broken. It looks like a thru hardened shaft but it's likely case hardened 8620 with a tough core. I'm not sure if it broke from a seized pump or maybe from flex resulting from something in between the drive gears?

msim · Nov 30, 2018

leedawg said:
How do you know high current severed your throttle cable? Does it look like an arc welder struck up where the cable is severed? Are you sure the sheath of the cable did not rub away on something or even worse rub through one of the main gen leads? There is a huge grounding braided strap that runs from the bell housing where the starter is to the battery perhaps you need to take this off and clean everything up from the corrosion. You did mention it was very weathered. Sounds like you will have to do this anyway based on the condition of the motor now anyway being that its going to be a partial rebuild or simply a motor swap. Again my .02 you cant rebuild that motor for less than the auction mentioned above especially if you factor your time in.

Also how are you getting a flame into the intake, with the air intake filter and hoses in place? Or did you take this off to do that if so what kind of air filtration is happening when the motor is running? Again sounds as though the set has a lot of neglected maint should just be able to preheat and fire it up that is how mine is, ive never had to so much as give it a squirt of ether just starts.

And to answer your question about the oil pump burning up from current flowing through im going to say no. It would take an incredible amount of current to do that and for a sustained period of time to burn up those parts just don't see that happening. That being said two 12 volt batteries do have enough current to weld with, ive done it while 4 wheeling and broke a suspension bracket. But they don't hold out long when you put them under that kind of load and there is no way the alternator puts out that kind of current. I think you just had a fluk failure of the oil pump you could attempt to replace it and see how she goes but as I said before the time and trouble think id just replace the whole motor knowing I am solving multiple problems with one stone.

Good luck!!! and I am sorry to hear about the troubles.

The throttle cable was severed from electric current at an area it came into contact around the generator. Molten strands, burned outer covering etc. I found the engine block/chassis ground strap in terrible shape and corrosion in any bolts in the area.
I still wonder why that happened. You would think the main gen has to be involved but I'm stumped. There certainly was a lack of current paths from front to back. When the throttle cable went, there was no electric in the instrument panel area until I fixed the ground problems.

For the 'enhanced starting', I pull the rubber hose off. I then might or might not put the hose back. As i said, the method came about when I worried low batteries might not do it. At low voltage it would take a lot of time to fire. With good batteries it always started quickly.

rustystud · Dec 1, 2018

msim said:
It looks like a pump in great shape aside from the shadt being broken.

I'm sorry but that pump is anything but in great shape ! There is damage all over !

DieselAddict · Dec 1, 2018

Have you inspected the bypass valve? Is it stuck closed?

Buickrat · Dec 1, 2018

The only thing that would shear the pump driveshaft is if a chunk, sometimes small, locked up the pump. Debris somewhere in that motor.

I had a car that did the same thing...3 times. Found out it was lifter retaining clips that got into the motor before a previous rebuild. Every time I took the oil pump apart, the gears had a small piece of wire in them that locked them up. It doesn't take much, especially if its hardened steel.

msim · Dec 1, 2018

I think I found it.
There was a squashed 3/16 x 3/4 roll pin on the ground below the front cover. It must have gotten in between the gears, forcing them apart and breaking the shaft.
It must be the one that is pressed into the cover and keeps the governor from rotating.
Looking at the support available I'm surprised this doesn't happen more often.

A roll pin is well oversize of the nominal hole and the installation is brutal, there's not enough support material here for that and aluminum is too soft. A roll pin is very wrong for this application.
The cover's hole on mine was swaged outward during installation with the pin retaining its shape, plowing as it was inserted. The pin is supposed to compress, not the hole. Now there's no spring force to hold it in .
If that weren't bad enough, it pokes up several times the amount installed and has side forces acting with leverage against the hole. It will only get looser over time , mine must have simply fallen out. Egads.
Are these all equipped with roll pins or dowels? The TM-5 manual's parts list calls it a "roll pin".

Rustystud, The drive gear is a bit 'rough' but the housing and gears are in exc shape, There is no scoring or measurable wear spots. The original machining looks uglier in pics than in person.
The clearances are not loose and seem to have been well controlled at the factory.

Deiseladdict, they put the bypass valve in the other end. Instructions to remove it start with:

(1) Remove generator, engine flywheel, and
adapter.

So where does one get parts? I need the oil pump gear/shaft, front cover and crank gear. Does anyone part these out? Any civilian Onan sources? I searched for an oil pump and found zero but there are a whole bunch of various Onan ones, plentiful and cheap. Are there no stocks of parts from their service time?

rustystud · Dec 2, 2018

There are several models of "civilian" ONAN generator engines that will have parts interchange with our MEPS. Call your local supplier of ONAN parts. Of course you can always put a "want add" here for a good used engine for parts.

Forgot to mention. Glad you found the culprit !

MEP-003A oil pump seized out of the blue

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