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techtalk:ref:oil21 [2024/04/04 01:27]
– [Flow Rate Chart for Water] hippysmack |
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techtalk:ref:oil21 [2024/09/29 20:49] (current)
– [Normal Oil Migration] hippysmack |
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| Due to the rotating gears and gearshaft, oil is pulled through the clearances. \\ |
| This is normal and the clearances are there to cut down on heat buildup and galling. \\ |
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| |**Dry Gear face clearance**: The gears in the pump have a top and bottom surface and by indusrty standards is called the (sides). I generally called that the (faces) since bikers would think the sides to be the area between the teeth and the sides of the gear bore in the pump. The face clearance in gear pumps is finally established by the cover gasket thickness. The gear height also plays a factor in that clearance. The installed gear height in the pump according to the 70-78 FSM is .0005" below to .0025 above the pump body gasket surface. The lower the gear sits in the gear well in the body, the more the clearance up top and the higher it sits, the less the clearance will be. So once the gasket and cover is installed, the running clearance is set. **Running Gear Face Clearance**: So now you should have lubed the gears before finally installing them in the pump to keep wear down on startup. When you fire up the motor, oil is pulled into the face clearances by the rotation of the gears and that "oil migration" should be, by design, a minimal amount of oil. The gears turn by the breather gear pins and/or pin and woodruff key respective of breather gear type. The pin/key is not a press fit in the slot of the gears so the gears have the ability to float up or down during operation. Oil is pulled into the face clearances and should be equal amounts on top and bottom of the gears as the gears adjust their height according to the pressure of the migrating oil each side. This should reduce the clearance that was measured during assembly by roughly 1/2 in a running pump. **Slippage**: We've established the clearances and designed amount of oil to be recirculated between the feed and return chambers. That clearance keeps gear to mating surfaces apart and provides cooling across the gear faces. The amount of oil lost from the feed chamber (due to recirculation) is commonly referred to as slip or slippage or recirculation. This is the crux of oil pump efficiency deciding how much oil the pump will carry between the teeth as opposed to how much can actually be delivered to the motor and at what percentage throughout the RPM changes. But another part of pump efficiency involves the teeth to pump wall clearance not discussed here. **What feeds oil across the gear faces**: On idle, as pressure builds in the outlet chamber of the pump, some of that pressurized oil pushes to the gear faces, into the clearances and rotates around to the pump suction chamber, still under pressure. **How face oil migration affects the suction of the gears**: If the migrating oil was not under pump pressure, it would simply be referred to as an additional oil inlet as far as the suction chamber goes. But the positive pressure into the suction chamber is now reducing the amount of effective vacuum that is being created by the closing of the gears. This does two main things; It lowers suction on the hose from the oil tank which in turn lowers the amount of oil pulled into the pump per revolution. It also creates more heat to the migrating oil in the process. |
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| Below is a drawing of a 1986-1990 Sportster Oil Pump. \\ |
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| {{:techtalk:ref:oil:sportster_oil_pressure_-_oil_pump_oil_migration_1977-1985_by_hippysmack.png?direct&400|}} ((drawing by Hippysmack)) {{:techtalk:ref:oil:sportster_oil_pressure_-_oil_pump_oil_migration_1986-1990_by_hippysmack.png?direct&400|}} ((drawing by Hippysmack)) \\ |
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| ===== System Pressure Loss From Internal Leakage (recirculating oil) ===== |
