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| techtalk:ref:engmech07h [2020/10/08 16:56] – [Oil Drainback and Supplemental Air Intake from Breather Valves] hippysmack | techtalk:ref:engmech07h [2023/12/26 20:42] (current) – hippysmack |
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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. |
| The 85 cover has the breather baffle tube system but the principles are the same and it doesn't appear the drain hole size changed. \\ | The 85 cover has the breather baffle tube system but the principles are the same and it doesn't appear the drain hole size changed. \\ |
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| |77 Cam Cover Breather Compartment \\ (no oil drainback). ((photo by joynny77 of the XLFORUM http://xlforum.net/forums/showthread.php?t=610444&page=4))|81 Cam Cover Breather Compartment \\ (w / rubber umbrella valve upgrade) \\ Oil drainback hole in dimple. ((photo by joynny77 of the XLFORUM http://xlforum.net/forums/showthread.php?t=610444&page=4))|85 cam cover w / baffle tube system. \\ Oil drainback in dimple. ((photo by billeuze of the XLFORUM http://xlforum.net/forums/showthread.php?t=1103082))| | |77 Cam Cover Breather Compartment \\ (no oil drainback). ((photo by jonny77 of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/82366-foo-foo-gone-or-was-it-ever-there-do-i-need-it/page3?t=610444&page=4))|81 Cam Cover Breather Compartment \\ (w / rubber umbrella valve upgrade) \\ Oil drainback hole in dimple. ((photo by jonny77 of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/82366-foo-foo-gone-or-was-it-ever-there-do-i-need-it/page4?t=610444&page=4))|85 cam cover w / baffle tube system. \\ Oil drainback in dimple. ((photo by billeuze of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/115252-cam-fitment-question-on-ih-help-me-out-plz?t=1103082))| |
| |{{:techtalk:ih:engmech:1977_crankcase_breather_compartment_by_johnny77.jpg?direct&300|}}|{{:techtalk:ih:engmech:1981_crankcase_breather_compartment_w_update_rubber_valve_by_johnny77.jpg?direct&300|}}|{{:techtalk:ih:oil:85_cam_cover_1_by_billeuze.jpg?direct&300|}} | | |{{:techtalk:ih:engmech:1977_crankcase_breather_compartment_by_johnny77.jpg?direct&300|}}|{{:techtalk:ih:engmech:1981_crankcase_breather_compartment_w_update_rubber_valve_by_johnny77.jpg?direct&300|}}|{{:techtalk:ih:oil:85_cam_cover_1_by_billeuze.jpg?direct&300|}} | |
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| The assembly was cut open in the pics below revealing the separation chamber and the drain hole. \\ | The assembly was cut open in the pics below revealing the separation chamber and the drain hole. \\ |
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| | View of one cut open. ((photos by Bored now of the XLFORUM http://xlforum.net/forums/showthread.php?p=5761087#post5761087)) || Oil drain hole. ((photo by dieselvette of the XLFORUM http://xlforum.net/forums/showthread.php?t=2073932&page=30)) | | | View of one cut open. ((photos by Bored now of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-general-discussion-and-problems/197352-oil-cap-problems-bikers-choice-02-073/page2#post4317318)) || Oil drain hole. ((photo by dieselvette of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-bottom-end/197307-sportster-crankcase-pressure-engine-breathing-wetsumping-and-mods/page30?t=2073932&page=30)) | |
| |{{:techtalk:evo:engmech:04_up_breather_1_by_bored_now.jpg?direct&300|}}|{{:techtalk:evo:engmech:04_up_breather_2_by_bored_now.jpg?direct&300|}}|{{:techtalk:ref:engmech:04_up_breather_valve_2_by_dieselvette.jpg?direct&300|}}| | |{{:techtalk:evo:engmech:04_up_breather_1_by_bored_now.jpg?direct&300|}}|{{:techtalk:evo:engmech:04_up_breather_2_by_bored_now.jpg?direct&300|}}|{{:techtalk:ref:engmech:04_up_breather_valve_2_by_dieselvette.jpg?direct&300|}}| |
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