The Oil Pump


Lee's oil pump, when machined to print, is a very effective and powerful pump set. It consists of two separate pumps, the pressure pump, which provides oil under pressure to most moving parts of the radial, and a scavenge pump. The scavenge pump retrieves oil from the crankcase and delivers it to an external oil tank. If you are familiar only with typical automobile systems, which use a wet pan at the bottom of the engine, a dry sump may be unusual at first, but it is the norm for a radial aircraft engine, and many motorcycles (such as the ubiquitous V-twins of a Harley) use a dry sump / scavenge system as well.

What looks to be a fuel tank on my engine is really a compartmentalized 2-part cylinder, one holding fuel, the other, oil.

Lee's pump set is made of aluminum. I created mine of bearing bronze, left over from the front and rear main bearings. This pump is very stout and durable, but also very heavy.

Rear view... the tail of the crankshaft is in the center of the pump, and drives two brass spur gears, which in turn drive a set of spur gear pumps inside the pump body. Hence, there are seven spur gears, three visible, and four hidden. The scavenge pump is at 7:00, and the pressure pump at 10:00 in this photo.

Mounted on the crankshaft. The pressure pump provides oil to the rear crank journal, and flows through internal channels to the master rod hournal, and thence to the forward bearing journal. Oil exits forward and is delivered centrifugally to the cam ring and tappets. Splash / centrifugal oil also wends its way to each rod, writst and knuckle pin, cylinder walls, and via a bit of oil blowby, to the tops (rockers) of each cylinder, at least that bit which isn't burned.

A somewhat closer view. Note the turned oil channel in the journal. Note too the two-piece cheeks. My small but effective impellor is also visible.

The pump is plumbed with these two stems, which extend through the rear crankcase cover, and from there...

... they flow via these little SS braided tubes to the external oil tank!

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