MEP-003A oil pump seized out of the blue

[Guyfang]

About 4 months ago, there was someone trying to sell several parts units. Both 5&10 KW. He was from Utah. And there are others for sure. Roll pins are standard sizes. So that's not a problem. Remember, you are assuming, and that can bite you in the patooty, assuming that's the only big piece floating around in there.

 

[rustystud]

Remember, you are assuming, and that can bite you in the patooty, assuming that's the only big piece floating around in there.

Very true !!!!

 

[leedawg]

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.

Wow so all the power for the 24v system was moving through the throttle cable that is some terrible grounding issues. Perhaps the starter fried the cable most of the way and then it just sore of broke from vibration. Werid a lot of current must have moved through that cable.

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".

View attachment 749670

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?

Glad you found the cause. Just because im not super familiar with the internals of this engine and hope to never be. This roll pin was pressed into the oil pan as a stop for something? How did it find its way past the oil pick up screen for the pump do ya think?

 

[Guyfang]

Are you sure it gets pressed into the oil pan? I find it hard to believe it got past the oil pump screen. Now you are asking the right questions. Got to think about this a bit.