RT--- Here's the thing. Unless your injection pump has been recently overhauled, the chances are great that a wee bit of fuel will be getting past the injection plungers on every stroke. The plungers are lubed by the fuel they pump. The oil in the pump's sump is simply to lubricate the drive mechanism in the lower part of the pump..
As the plungers work, they and the sides of the bores they run in wear. It's the nature of the beast, and is why in this type of jerk-injection system (that's what it's called) fuel lubricity is critical. This is why a lot of FL120 operators including us use a lubricity additive in their fuel.
As the plungers and bores wear, more and more fuel gets past the plungers and goes down in the lube oil below. As this happens the level of lube oil in the sump increases as it is diluted by the fuel.
The reason for the 50 hour oil change on the pump is to ensure that even with a fair amount of fuel getting into the oil, it never gets so diluted that it does a poor job of lubricating the pump drive mechanism.
This is the reason for the breather fitting, usually a banjo bolt, fitting and tube, at the rear end of the pump. It also acts as a means for excess lube oil to escape.
But it can make a mess as you note, and with the engine tilted back, even the "correct" amount of lube oil can cause some to be blown out the breather.
Bob Smith at American diesel gave me his recommendation for dealing with this. First, plug the breather fitting at the rear of the pump by replacing the banjo connector on the plug with a stainless nut with a compressible washer (aluminum or brass) on each side of it. This blocks the breather hole in the hollow banjo bolt.
Of course the pump still needs to "breathe" and this is accomplished by drilling a small hole in the middle of the oil fill screw cap on top of the pump.
I plugged the side breather banjo bolt using a nut and two aluminum washers as instructed by Bob, and when I went to drill the breather holes in the oil fill plugs, found that someone had already done so down in the center of the slot in the head.
So no no more mess. If one has a pump that has a fair amount of fuel leak-by at the plungers so that the pump "makes" a lot of lube oil, the excess can be drained off at the level plug at the forward end of the pump.
Eventually the plunger/bore wear will reach the point where the injection shots themselves are affected and the engine will begin to run poorly. At that point, the pump needs to be overhauled.
When I change the oil in our pumps, after draining the old oil I remove the level plug and fill the pump until oil starts coming out of the level hole. I let any excess oil come out and then I replace the level hole plug.
That's it until I repeat the process 50 hours later. I don't have to measure anything out, and since the side breather hole is now plugged, nothing gets blown out of the pump.
Photo is the side of the pump on our port engine.
