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techtalk:ref:engmech07h [2020/10/08 16:56] hippysmack [Oil Drainback and Supplemental Air Intake from Breather Valves] |
techtalk:ref:engmech07h [2020/10/08 19:36] hippysmack [Oil Drainback and Supplemental Air Intake from Breather Valves] |
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| ====== REF: Engine Mechanicals - Sub-07H ====== | ====== REF: Engine Mechanicals - Sub-07H ====== | ||
| ====== Oil Drainback and Supplemental Air Intake from Breather Valves ====== | ====== Oil Drainback and Supplemental Air Intake from Breather Valves ====== | ||
| - | 1979-up Sportster engine crankcase breather valve assemblies all have a tiny oil/air drainback hole installed on the outside of the breather valve. \\ | + | |
| + | Vacuum is created in the bottom end on 1957-present engines due to piston upstroke (actually that's the same in any internal combustion engine). \\ | ||
| + | The volume of air under them increases without any or much air intake behind to fill the void. \\ | ||
| + | This leaves a lower differential pressure underneath and measured as negative pressure (or vacuum). \\ | ||
| + | |||
| + | **1957-1976 Sportster engines** use a timed rotary breather valve to control when and how much vacuum is created in the crankcase. \\ | ||
| + | As pistons begin to rise, the valve is still open. So vacuum is not built until after the valve closes farther up the cylinder. \\ | ||
| + | When pistons rise, vacuum is created under them and air pressure is brought into the crankcase from the gearcase vent until the breather closes. \\ | ||
| + | So there is an air intake into the crankcase from atmosphere until the valve closes. | ||
| + | |||
| + | **1979-up Sportster engines** use a one way breather valve and the breather valve assemblies all have a tiny oil / air drainback hole. \\ | ||
| + | It's installed on the outside of the breather valve. \\ | ||
| * The breather valve has a built in pocket in the cam cover (see pics below). | * The breather valve has a built in pocket in the cam cover (see pics below). | ||
| * Air / oil mist enters the pocket and flows past the valve. | * Air / oil mist enters the pocket and flows past the valve. | ||
