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techtalk:ref:engmech04 [2023/12/22 20:25] – [Symptoms of High Crankcase Pressure] hippysmacktechtalk:ref:engmech04 [2024/11/30 06:52] (current) – [Differential Pressure (vacuum and air pressure)] hippysmack
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 More molecules inside the engine than outside = inside air pressure. \\ More molecules inside the engine than outside = inside air pressure. \\
 Less molecules inside the engine than outside = inside is vacuum pressure. \\ Less molecules inside the engine than outside = inside is vacuum pressure. \\
-57-76 engines are subject to the most volume of vacuum in the crankcase, rocker box, oil tank and primary compartments. \\+57-76 engines are subject to the most volume of vacuum in the crankcase. \\
 77-85 engines are subject to the same volume of vacuum in the gearcase, rocker box, oil tank, gearcase and primary compartments. \\  77-85 engines are subject to the same volume of vacuum in the gearcase, rocker box, oil tank, gearcase and primary compartments. \\ 
  
 Oil scavenging: \\ Oil scavenging: \\
-Positive crankcase air pressure aids scavenging. It pushes the oil to the oil pump. \\ +Positive crankcase air pressure aids scavenging. \\ 
-Negative (vacuum) pressure makes the pump's job harder. High vacuum makes the downstroke push to scavenge less powerful. \\ +It pushes oil against the suction chamber of the pump creating more Net Positive Suction Head Available (NPSHA) to the pump which is a requirement of the pump design. \\ 
-The oil pump wants to receive more oil, high vacuum slows down the delivery of oil to the oil pump. \\+This push is needed in order to assure there will be oil at the suction inlet of the pump especially upon higher RPM. \\ 
 +With lower NPSHA, the oil may may not enter the pump's suction chamber fast enough which can lower the amount of oil the pump will pump. \\ 
 +Negative (vacuum) pressure on the incoming oil makes the pump's job harder. Vacuum makes the downstroke push to scavenge less powerful. \\ 
 +The oil pump wants to receive more oil on higher RPM. Higher vacuum is created in the suction chamber near the gears as the pump speeds up. \\ 
 +Without a positive "push" ushering the oil to the suction chamber, vacuum in the chamber can slow (or partially choke) oil coming into the chamber. \\ 
 +This slows down the delivery of oil to the oil pump (lowers NPSHA) and can result in wetsumping the motor. \\
  
 Ring seal and pumping loss: \\ Ring seal and pumping loss: \\

Trace: • REF: Engine Mechanicals