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Today's work explored the lubrication system some more.
The oil pump is located at the back of the engine, actually behind the mounting bulkhead. For most installations, that will put it in the front of the cockpit. There's a large inlet and a small pressure outlet. The oil seems to go externally to the engine to a fitting at the top back of the engine, and another at the bottom front.
In the first picture, the inlet fitting is shown loosely installed at the bottom of the oil cavity. It's got a white tag hanging from it. The hand is holding the tachometer drive cover next to the tach drive shaft. The tachometer drive is 1/2 engine speed, in the reverse direction (counter-clockwise here).
The second picture is a poor one of the inside of the oil pump. Unfortunately it doesn't include the piston. It does show the brass pump body, the tapered oil pressure outlet line with the inside showing, and the check valve spring, retainer and ball. The check valve retainer has a square hole, so that even when the ball is blocking it, some oil can escape. This probably helps the return spring push the pump piston back.
The return spring isn't shown. In fact, I'm not sure we have it. The piston weighs 18 grams, and we know the dimensions of what the spring must be, so I'll see if I can find a stock spring. If not, I'll design one.
In both cases the oil flows through the case to the crankshaft, where it goes through passageways to the ball bearings - this engine uses ball bearings - on either side of the two throws of the crankshaft, there's no bearings in the middle. There's a bearing at the very front of the case that the prop hub seems to retain, and one more in the accessory case at the back.
In the case, the front case has ample drainage and the rear case minimal drainage. The low drainage in the back is probably a way to ensure that the gears are lubricated. At the bottom of the case, there's a drain plug for the front and the back crankcase halves, and on top, a breather for each.
At the back, there's an internal copper tube that goes from the pressure oil fitting to the rear crankshaft journal at the cam. That copper tube appears to be cast in place.
Incidentally, the casting and machining on this engine is first-rate.
The drain plugs are clearly not intended for daily use. They are at suitable locations for a possible oil return system, and I believe that I have a service bulletin recommending that. If so, then we don't know what the oil return pump should be.
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