This is the small oil pump that is used to lift oil out of the bottom sump of the 1914 Mercer Raceabout’s four-cylinder engine. It is transferred to a glass-faced sight gauge on the dash through fittings and tubing, then it pumps through the gauge where you can see the flow.
At idle, the flow is only enough to maybe fill half a cup of oil in 30 seconds. At speed things pick up and there is quite a flow through the gauge which then drains thru 5/16-inch tubing and fittings and back into the crankcase and it drops into a oil trough above the center main bearing from were it flows by gravity to lube the bearing.
The rest off the engine is lubed by a splash system with troughs above all the main and cam bearings. Other than the center main, these troughs fill from the mist and droplets of oil that we hope falls in them. Many early engines relied on this method which is a far cry from a pressure system which has been in use since around 1905. My friend George Wingard put it very well in his book where he mentions the brilliant engine design of the Mercer which in use won a lot of races, backed up by an oiling system about as sophisticated as the irrigation system for a rice paddy.
The pump is quite ingenious and works by using an offset pin in the cover which sits in the hollow end of the pump shaft on the left. As the pump rotates, the pin being offset causes the insert you see in the shaft to move back and forth. It is in the position you see it now on the right were oil goes into the cavity from a hole in the side of the housing it then rotates 180 degrees and the pin forces it out ejecting the oil it carried around into the fitting on the left side of the housing and out of the pump. It was in very good condition only had .001″ clearance between it and the housing. The clearance between the pump shaft and the cover needs to be around .001 also and was adjusted with a hard phosphor bronze washer I machined. The pump shaft also needed to be replaced, it is two pieces and was worn on the end and where it is driven by the gear drive we rebuilt earlier. We made a new one out of pre hardened chrome moly.
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