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techtalk:ref:engmech04k [2023/12/20 22:22] – hippysmacktechtalk:ref:engmech04k [2025/09/06 19:40] (current) – [Breather Valves (1957-Up)] hippysmack
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 This allows crankcase exhaust air pressure and scavenge oil in the crankcase to be expelled from the crankcase to the breather oil trap and into the gearcase. \\ This allows crankcase exhaust air pressure and scavenge oil in the crankcase to be expelled from the crankcase to the breather oil trap and into the gearcase. \\
 The breather valve closes during piston upstroke, creating a controlled amount of vacuum in the crankcase. \\ The breather valve closes during piston upstroke, creating a controlled amount of vacuum in the crankcase. \\
-**The 1952-1971** breather valve opens at 77° (ATDC) and closes 67° (ABDC). \\ +**The 1952-1971** breather valve opens at 25° (ATDC) and closes at (BDC). \\ 
-**The 1972-1976** breather valve opens 20°-25° (ATDC) and closes 85°-90° (ABDC), less duration than the 57-71 breather. \\+**The 1972-1976** breather valve opens 20°-25° (ATDC) and closes 85°-90° (ABDC). \\
  
 |Left is the unmodified 1/4 speed R \\ valve. Right is the 1000 stock.|R model is the left one.| |Left is the unmodified 1/4 speed R \\ valve. Right is the 1000 stock.|R model is the left one.|
 |{{:techtalk:ih:engmech:cc_flow_4_by_dr_dick.jpg?direct&200|}}|{{:techtalk:ih:engmech:cc_flow_5_by_dr_dick.jpg?direct&300|}}| |{{:techtalk:ih:engmech:cc_flow_4_by_dr_dick.jpg?direct&200|}}|{{:techtalk:ih:engmech:cc_flow_5_by_dr_dick.jpg?direct&300|}}|
  
-**1977-78 models only**: ((Hopper of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/74149-engine-breather-101-crankcase-vent-101?t=518948&highlight=cam+chest+breather)) \\+**1977-1978 models only**: ((Hopper of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/74149-engine-breather-101-crankcase-vent-101?t=518948&highlight=cam+chest+breather)) \\
 The timed breather on the oil pump drive was dropped.  \\ The timed breather on the oil pump drive was dropped.  \\
 Without the breather gear that means you have less control of the oil / air density in the crankcase. \\ Without the breather gear that means you have less control of the oil / air density in the crankcase. \\

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