MODEL 348 OIL PUMP
A triple gear feed pump and a double gear large capacity scavenging pump are built into a single unit.
The feed pump center (driving) gear (4) does not pump oil. The bottom (driven} gear (3) forces more oil than the engine requires to the pressure side of the pump. The upper (metering) gear (5), 0.017″ thinner than the other gears, pumps oil in the opposite direction at a slower rate. The metering action between the top and bottom gears governs the amount of oil delivered to the engine.
When installed, the pump must have oil in the gears for lubrication and priming. If not, force oil into feed pump elbow in pump housing. Bleed the oil feed line at the elbow connection until clear oil, free of bubbles , flows from the line.
The reverse safety valve (6), a 1/8″ ball and flat spring on pump body cover, must have a positive seal to prevent air leaks. The feed pump will suck air instead of drawing No. 7 ball check valve open to allow oil to flow to the gears if there is an air leak at safety valve (6).
Two 5/16″ ball check valves are used to prevent seepage to crankcase. In some cases, it is advisable to remove the upper valve (7) from the pump body to assure a positive flow of oil to the feed gears, particularly in cold weather when the oil congeals. Do not remove valve (8) between pump housing and cam case cover.
The scavenging gears (1 & 2.) can be primed with a small amount of oil dropped into the return line, or at the nipple. Before starting the engine, 1/2 pint of oil must be put in the crankcase . The sump oil line (9) must be tight and sump elbow with screen (10) must be clean. A dirty or clogged screen will prevent the oil from returning to the tank as it should, and the result will be “wet sumping”, overheating of the engine and high oil consumption. Be sure to clean this screen every time the oil is changed (500 to 1000 miles).
Walter Brown
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