MEP002A Oil Pump

[Guyfang]

I have known and worked on this type gen set and engine,since 1973. And this engine is used on more equipment then you would even guess. NEVER have I seen this failure. Good job!

 

[Boonies]

Here is some info I pulled from a copy of an Onan DJB manual that may help:

"OIL PUMP The oil pump is mounted on the front of the crank case behind the gear cover and is driven by the crankshaft gear. Rem oval: 1. Remove gear cover and oil base. (See ENGlNE 2. Unscrew intake cup from pump. 3. Remove crankshaft lock ring and gear-retaining 4. Loosen two cap screws holding pump and DlSASSEMBLY section.) washer. . remove' pump.

Repair: Except for the gaskets, component parts of the pump are not individually available. If the pump is defective or excessively worn, replace it. Disassemble the pump by removing the two cap screws holding the pump cover to the body. Inspect for excessive wear in gears and shafts. To improve pump performance, adjust the gear end clearance by changing the gasket thickness between the pump body and cover. Use the thinnest gasket that permits free movement of the pump shafts. Oil all parts when assembling the pump.

Installation: Before installing, fill-the pump intake and outlet with oil to be sure it is primed. Mount the pump on the engine and adjust the 0.005-inch (0.127 mm) lash between the pump gear and crankshaft gear. Mount the intake cup on the pump so it is parallel to the bottom of the crankcase.

Here are some torque settings that may be helpful:

TORQUE SPECIFICATIONS Ft.-Lb.

OIL Pump Mounting Screws 15 - 20 Ft Lbs

Thanks again for all the help! The new pump should be here by the end of the week. I have the repair partially closed up to keep it clean. Will take photos when new pump is here and installing it. Will post them at end of week.

 

[Ray70]

Interesting... a little while ago I bought a used 4 cyl. motor ( I wanted the IP )
Out of curiosity I tore it down to see why the motor failed.
The oil pump shaft was also sheared off, but the crank gear was also split in half right where the threaded gear puller holes are.
I assumed the crank gear somehow exploded and took out the oil pump.... BUT, maybe it was actually the other way around??

 

[Chainbreaker]

Since you ran the engine after your oil change with a new oil filter and it ran for 1.25 hrs until the oil pressure safety circuit shut it down, obviously that means the shaft/gear broke then. It might be a good idea to see if you can open up the prior oil filter it was running on if you still have it, to see if there are any significant metal particles that were captured in the filter. Or...if there was a "foreign object" that is not part of the gear/shaft that may have passed through the gear teeth & binding gear/shaft causing it to fracture/break. Just a thought...

 

[Boonies]

Wow glad you found the problem! This is the first ever oil pump failure I have heard of on a MEP-002a/-003a. I wonder why the oil pump drive gear decided to break off at 6,414 hours? Wonder if there was an inherent defect in the gear shaft metallurgy all along and years of heat/cooling thermal cycling plus time took its toll? Glad that it didn't suffer a more catastrophic failure with significant engine damage!

If you have the time it would be great if you could post some close up photos of where the break occurred on that gear shaft and of the gear toothed portion.

Here are some photos. Turns out that after the gear sheared it was apparently still contacting the crank gear and spinning and banging around. The crank gear had no signs of any damage at all. The probably make the crank gear out of a much more durable harder steel. There was a hole in the gear cover I had to patch with metalized epoxy putty. The shear itself looked really clean and crisp. It was all the banging around that looked bad. Because of this I decided to drop the oil pan and be sure all metal was completely cleaned out. Much bigger job, but the new pump is in and purrs like a kitty, or shall I say, roars like lion!

 

[Guyfang]

Again, good job!

 

[Chainbreaker]

Very strange failure. The mystery remains as to what caused the oil pump gear shaft to break at that particular point along its shaft after 6k+ hours.

Either the shaft had a mfg defect, or something ended up getting lodged between the teeth and created enough force between the mating gear that it snapped the shaft. No way to know unless you were to find a foreign object in oil pan or oil filter you previously removed: perhaps a metallic object that was in the new filter, or something broke off an internal engine part with path to oil.

 

[Boonies]

Very strange failure. The mystery remains as to what caused the oil pump gear shaft to break at that particular point along its shaft after 6k+ hours.

Either the shaft had a mfg defect, or something ended up getting lodged between the teeth and created enough force between the mating gear that it snapped the shaft. No way to know unless you were to find a foreign object in oil pan or oil filter you previously removed: perhaps a metallic object that was in the new filter, or something broke off an internal engine part with path to oil.

There was a small amount of metallic sludge in the oil pan and some super fine shavings but no "pieces" of metal. The oil path is straight out of the oil pan through the oil cup which has a fine mesh screen on it and then directly to the pump and from the pump directly to the oil filter. Anything that got into the gears of the oil pump had to come out of the oil pan through the screen. The sludge could go through the screen if got mixed into the oil in the pan, but it doesn't seem possible for the shavings I found to go through the screen. I don't know?
Is there some way that something could get in the gear cover and then get into the teeth of the outer oil pump gear and crankshaft gear? What would that be and where would it come from?
I don't know if you can see in the photo of the gear cover, but the shiny spot to the left of the hole is where the pump gear was apparently still spinning and shaving off metal from the gear cover. The time it took for the engine to stop after the pump broke plus the 4 or 5 times I cranked it after the failure added up to a total of about 30 seconds or so that the gear could have been spinning and banging around. Maybe about 1/16th" of metal was shaved away from an approximate ¾ square inch spot. I think some of the metal shavings I found in the oil pan may have come from the gear cover. There are openings around the oil pump where stuff under the gear cover can get back directly into the oil pan. I do still have the oil filter from the oil change I did 1.25 hours before the pump broke. I haven't had time to open it up, but I will do that.

 

[Chainbreaker]

Once you remove the old oil pump maybe you should see if you can take it apart and inspect internals of oil pump itself?

I just feel like there is more to the story here... One SS member here ran his MEP-002a for 22000 hours and said he couldn't kill it! Of course, not all parts for same model genset are sourced from same mfg. year-to-year.

 

[Boonies]

Once you remove the old oil pump maybe you should see if you can take it apart and inspect internals of oil pump itself?

I just feel like there is more to the story here... One SS member here ran his MEP-002a for 22000 hours and said he couldn't kill it! Of course, not all parts for same model genset are sourced from same mfg. year-to-year.

I finally had time to open the Oil filter that I had put on the machine after an oil change 1.25 hours before the oil pump broke. It was totally clean. No metal or any foreign debris of any kind that I could find. I also took apart the old oil pump. There was no internal damage or dings or marks anywhere inside the pump. I few places in this thread you mentioned thermal stress. I remember that about 5 years ago the thermal expansion cylinder that opens and closes the air louvers on the exhaust output for the cooling system stopped working. The louvers didn't open and the generator died when the thermal cutoff switch opened. This is what is supposed to happen, but non-the-less the engine got pretty hot before the switch opened. Unfortunately, I didn't diagnose the problem accurately and it happened again. Then I figured it out and fixed it. So, there were two known incidences of overheating. Maybe this is a factor?

 

[Chainbreaker]

Good job on doing the necropsy! From the sounds of it, the gear shaft just failed. Might have had a small flaw in the gear shaft during manufacturing. Regardless it went 6k+ hours before failure. So gear/shaft had a reasonably long life never-the-less.

I don't think your louvers not opening once and shutting down at a thermal cut off temperature would have had anything to do with it. Remember the engine also has an oil cooler that gets fed ambient air from the blower wheel, so oil should still have cooling.

 

[Blade70301]

I just had the same failure. It was the roll pin in the aluminum cover that fell into the gear set and caused catastrophic failure.

 

[Chainbreaker]

I just had the same failure. It was the roll pin in the aluminum cover that fell into the gear set and caused catastrophic failure.

Just out of curiosity... how many hours on the engine when your pump met its demise? Just wondering if there is a trend of any sort developing.
beyond a certain hour range.

 

[Guyfang]

Bad oil pump is a rare bear.

 

[Chainbreaker]

Yep, the oil pump was good until the foreign object, loose roll pin, entered the scene and tried to mate with the oil pump.

 

[Blade70301]

Just out of curiosity... how many hours on the engine when your pump met its demise? Just wondering if there is a trend of any sort developing.
beyond a certain hour range.

Just out of curiosity... how many hours on the engine when your pump met its demise? Just wondering if there is a trend of any sort developing.
beyond a certain hour range.

My generator had 850 hrs. It had a serious overload and shut down on temperature. Ran for 12 hrs. after overload and lost oil pressure. Found oil pump and gears destroyed. Roll pin on cover fell out.

 

[Blade70301]

 

[Guyfang]

Good job. And posting pictures is number 1! So few people do that.

 

[Chainbreaker]

Wow, two oil pump failures caused by roll pin coming out. Interesting that both units had over temp shutdown.

Sounds like the roll pin capture seat in cover expanded more than the roll pin to the point it lost its holding friction. Perhaps there were some manufacturing defects issues in the cover itself, or roll pin, where the mfg tolerances were off?

Would be interesting to know the serial #'s of each unit and dates of mfg. Also, wonder if perhaps incorrect temperature sensors were installed, or their trigger temp tolerances were off, causing higher than spec'd shutdown temperature...?

BTW, I had one of my -002s during a summer pwr outage that I loaded pretty hard that I'm fairly confident shut down due to overtemp. So far, it hasn't had any more problems and running temps seem normal when I checked afterwards with IR temp gun.

 

[ageregunner]

Thanks to all who posted on this problem. This is one of the best threads I have ever followed on a MEP-002 problem. Like Guyfang said, the photos and the video are priceless.