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techtalk:ref:engmech04 [2020/10/06 19:19] – [Engine breathing mods in general] hippysmacktechtalk:ref:engmech04 [2024/11/30 06:52] (current) – [Differential Pressure (vacuum and air pressure)] hippysmack
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 ====== Evo Crankcase Pressure and Engine Breathing ====== ====== Evo Crankcase Pressure and Engine Breathing ======
  
-See also in the REF section of the Sportsterpedia: \\ +\\
-  * [[techtalk:ref:oil10#refoiling_lubrication|Wet Sumping]] +
-  * [[techtalk:ref:oil05#engine_and_primary_oil_system_modifications|Engine and Primary Oil System Modifications]]+
  
 ====== Engine Breathing ====== ====== Engine Breathing ======
- +**The one way breather style system is more like a car PCV system**. ((mrmom9r of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/122424-breather-diagrams/page4?t=1204854&page=4)) Unlike an auto PCV, a Sportster has a faster acting type one way valve. \\ 
-**The one way breather style system is more like a car PCV system**. ((mrmom9r of the XLFORUM http://xlforum.net/forums/showthread.php?t=1204854&page=4)) Unlike an auto PCV, a Sportster has a faster acting type one way valve. \\ +
 A deep (dry) sump was added to 77> casings and the scavenge side of the oil pump pulls the oil from the scavenge port in the rear of the sump area. \\ A deep (dry) sump was added to 77> casings and the scavenge side of the oil pump pulls the oil from the scavenge port in the rear of the sump area. \\
 Holes were added between the crankcase and the gearcase wall (much the way your car's crankcase is vented out the top thru the valve covers) \\ Holes were added between the crankcase and the gearcase wall (much the way your car's crankcase is vented out the top thru the valve covers) \\
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 So the gearcase is also pressurized. Crankcase pressure is sent thru the one way valve in the cover and then vented to atmosphere out the vent. \\ So the gearcase is also pressurized. Crankcase pressure is sent thru the one way valve in the cover and then vented to atmosphere out the vent. \\
  
-**However, crankcase ventilation works a little differently on these motors than a Chevy**. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1468237)) \\+**However, crankcase ventilation works a little differently on these motors than a Chevy**. ((aswracing of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/135598-crankcase-pressure?t=1468237)) \\
 What you see on cars is an inlet, generally coming from the air filter, into the motor. Then an outlet, regulated by a PCV valve, going into the intake manifold. \\ What you see on cars is an inlet, generally coming from the air filter, into the motor. Then an outlet, regulated by a PCV valve, going into the intake manifold. \\
 So it's designed to flow a little air through the system. \\ So it's designed to flow a little air through the system. \\
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 ==== 1986-Up Engine Breathing Cycle ==== ==== 1986-Up Engine Breathing Cycle ====
- 
 A mixture of crankcase air and oil mist is produced on each piston down stroke. \\ A mixture of crankcase air and oil mist is produced on each piston down stroke. \\
 Upstroke pulls oil up into suspension but in tiny particles to mix with the air moving around and thrown here to there for lubrication in the crankcase. \\ Upstroke pulls oil up into suspension but in tiny particles to mix with the air moving around and thrown here to there for lubrication in the crankcase. \\
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 ==== 1986-1990 Engine Specifics ==== ==== 1986-1990 Engine Specifics ====
- 
 The air/oil mix is blown from the crankcase into the gearcase through holes in the cam wall where it lubes moving parts and separates. \\ The air/oil mix is blown from the crankcase into the gearcase through holes in the cam wall where it lubes moving parts and separates. \\
 After initial separation, the remaining air/oil mix is blown to a one way umbrella valve in the cam cover. \\ After initial separation, the remaining air/oil mix is blown to a one way umbrella valve in the cam cover. \\
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 At that point, the tiny hole is a slight air (atmosphere) intake hole. \\ At that point, the tiny hole is a slight air (atmosphere) intake hole. \\
  
-The crankcase air pushes past each breather valve and exits through the heads. \\ +The crankcase air pushes past the breather valve and exits the engine out the breather vent (which is factory plumbed into the air cleaner backing plate). \\ 
-A hole in each head connects the path from the outlet of the breather vent to atmosphere. \\ + 
-A hollow bolt installed into each head passes the air into the air cleaner backing plate. \\ +{{:techtalk:evo:engmech:86-90_cc_pressure_drawing_by_hippysmack.jpg?direct&300|}} ((drawing by Hippysmack)) {{:techtalk:evo:engmech:86-90_engine_crankcase_breathing_by_hippysmack.jpg?direct&300|}} ((drawing by Hippysmack))
  
 ==== 1991-2003 Engine Specifics ==== ==== 1991-2003 Engine Specifics ====
- 
 The air/oil mix is blown from the crankcase into the gearcase through holes in the cam wall where it lubes moving parts and separates. \\ The air/oil mix is blown from the crankcase into the gearcase through holes in the cam wall where it lubes moving parts and separates. \\
 The holes in the cam wall changed sizes also from 91-03. \\ The holes in the cam wall changed sizes also from 91-03. \\
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 At that point, the tiny hole is a slight air (atmosphere) intake hole. \\ At that point, the tiny hole is a slight air (atmosphere) intake hole. \\
  
-The crankcase air pushes past each breather valve and exits the engine out the breather vent (which is factory plumbed into the air cleaner backing plate). \\+The crankcase air pushes past each breather valve and exits through the heads. \\ 
 +A hole in each head connects the path from the outlet of the breather vent to atmosphere. \\ 
 +A hollow bolt installed into each head passes the air into the air cleaner backing plate. \\ 
  
-==== 2004-Up Engine Specifics ====+{{:techtalk:evo:engmech:91_and_up_cc_pressure_drawing_by_hippysmack.jpg?direct&300|}} ((drawing by Hippysmack)) {{:techtalk:evo:engmech:91-up_engine_crankcase_breathing_by_hippysmack.jpg?direct&300|}} ((drawing by Hippysmack))
  
 +==== 2004-Up Engine Specifics ====
 2004-up engines blow the air/oil mix out by the pinion gear bearing where it bounces around and is separated as before. \\ 2004-up engines blow the air/oil mix out by the pinion gear bearing where it bounces around and is separated as before. \\
 The holes in the cam wall were resized and repurposed to act as feed oil galleys for oil jets to spray the pistons. \\ The holes in the cam wall were resized and repurposed to act as feed oil galleys for oil jets to spray the pistons. \\
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 A hole in each head connects the path from the outlet of the breather vent to atmosphere. \\ A hole in each head connects the path from the outlet of the breather vent to atmosphere. \\
 A hollow bolt installed into each head passes the air into the air cleaner backing plate. \\  A hollow bolt installed into each head passes the air into the air cleaner backing plate. \\ 
-   
-==== OEM oil paths and engine breathing drawings ==== 
  
 +{{:techtalk:evo:engmech:91_and_up_cc_pressure_drawing_by_hippysmack.jpg?direct&300|}} ((drawing by Hippysmack)) {{:techtalk:evo:engmech:91-up_engine_crankcase_breathing_by_hippysmack.jpg?direct&300|}} ((drawing by Hippysmack))
 +
 +==== OEM oil paths and engine breathing drawings ====
 |  86-90 engine breathing paths. ((drawing by Hippysmack))  |  91 engine breathing paths. ((drawing by Hippysmack))  | |  86-90 engine breathing paths. ((drawing by Hippysmack))  |  91 engine breathing paths. ((drawing by Hippysmack))  |
 |{{:techtalk:ref:engmech:86-90_sportster_engine_breathing_by_hippysmack.jpg?direct&300|}}|{{:techtalk:ref:engmech:91_sportster_engine_breathing_by_hippysmack.jpg?direct&300|}}| |{{:techtalk:ref:engmech:86-90_sportster_engine_breathing_by_hippysmack.jpg?direct&300|}}|{{:techtalk:ref:engmech:91_sportster_engine_breathing_by_hippysmack.jpg?direct&300|}}|
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 |  92-97 engine breathing paths. ((drawing by Hippysmack))  |  98-03 engine breathing paths. ((drawing by Hippysmack))  |  04 and up engine breathing paths. ((drawing by Hippysmack))  | |  92-97 engine breathing paths. ((drawing by Hippysmack))  |  98-03 engine breathing paths. ((drawing by Hippysmack))  |  04 and up engine breathing paths. ((drawing by Hippysmack))  |
 |{{techtalk:ref:engmech:92-97_sportster_engine_breathing_by_hippysmack.jpg?direct&300|}}|{{techtalk:ref:engmech:98-03_sportster_engine_breathing_by_hippysmack.jpg?direct&300|}}|{{techtalk:ref:engmech:04_and_up_sportster_engine_breathing_by_hippysmack.jpg?direct&300|}}| |{{techtalk:ref:engmech:92-97_sportster_engine_breathing_by_hippysmack.jpg?direct&300|}}|{{techtalk:ref:engmech:98-03_sportster_engine_breathing_by_hippysmack.jpg?direct&300|}}|{{techtalk:ref:engmech:04_and_up_sportster_engine_breathing_by_hippysmack.jpg?direct&300|}}|
- 
  
 ====== Engine Breather Valves ====== ====== Engine Breather Valves ======
 ===== Sub Documents ===== ===== Sub Documents =====
   * [[techtalk:ref:engmech04k|Breather Valves (1957-Up)]] (list of breather valve changes)   * [[techtalk:ref:engmech04k|Breather Valves (1957-Up)]] (list of breather valve changes)
 +  * [[techtalk:ref:engmech04j|Further Study of Evo Sportster Breather Valves]]
 +  * [[techtalk:ref:engmech07h|Oil Drainback and Supplemental Air Intake from Breather Valves]]
   * [[techtalk:ref:engmech05|Breather Venting / Relocation]] (list of breathing mods and aftermarket breathers)   * [[techtalk:ref:engmech05|Breather Venting / Relocation]] (list of breathing mods and aftermarket breathers)
   * [[techtalk:ref:engmech04l|Head Vents vs Cam Chest Vent]]   * [[techtalk:ref:engmech04l|Head Vents vs Cam Chest Vent]]
 +  * [[techtalk:ref:oil10#refoiling_lubrication|Wet Sumping]]
   * [[techtalk:ref:engmech04m|Why Oil Pukes Out the Breather]]   * [[techtalk:ref:engmech04m|Why Oil Pukes Out the Breather]]
  
-==== Symptoms of Breather problems ==== +==== Symptoms of Breather Valve Problems ==== 
- +**The most notable signs of breather valve problems include weeping / leaking gaskets or blown gaskets / seals**. \\ 
-**The most noticeable signs of breather valve problems are weeping gaskets or oil excessively leaking out the breather or puking oil out of it**. \\ +L82-up rubber umbrella(s) get hard and if they don't flex well enough, they'll allow the engine to fully inhaler and exhale on every stroke uncontrolled. \\ 
-When the umbrella(s) gets hard, it doesn't flex well to allow the engine to breath out on exhale. \\ +Stopped up breather valves won't allow the engine to breath well and can create excess vacuum and implode gaskets. \\
-Then the trapped in air is compounded on the next stroke.  The excess air contributes to more vacuum created and implodes the gaskets. \\+
 Or it contributes to too high of oil density and slings excess oil out. Other factors are involved so results will vary. \\ Or it contributes to too high of oil density and slings excess oil out. Other factors are involved so results will vary. \\
 +However, a slight amount of oil in mist form coming out the vent/air cleaner is totally normal and does not quantify as puking oil. \\
  
-**Wetsumping during shutdown periods is a condition of bad oil pump sealing, bad check valve or regulator (if equipped) sealing**. \\ +**Wetsumping can be a result of poor engine breathing but not always**. \\ 
-[[techtalk:ref:oil10#wet_sumping|Click here]] to read the full article on wetsumping in the REF section of the Sportsterpedia. \\ +Blowing oil out after extended shutdown periods is a condition of bad oil pump sealing, bad check valve or regulator (if equipped) sealing. \\ 
- +Blowing oil out the vent/air cleaner during riding first looks to the oil tank being overfilled. \\ 
-The foregoing addresses the affects of wetsumping upon with the engine running. \\ +If the engine is not at operating temp before checking the oil level, you'll end up adding too much oil to the system. \\ 
-Later engines are not competition engines. Maybe the earlier Sportsters were, but those days are long gone. ((chevelle of the XLFORUM http://xlforum.net/forums/showthread.php?t=1204854&page=3)) \\ +Blowing oil out the vent/aircleaner during high sustained RPM may be high crankcase pressure or poor oil scavenging. \\ 
- +Also see the full article on wetsumping in the sub documents above. \\
-**Wetsumping (at sustained high RPM) is a condition when the oil pump isn't removing the oil as fast as it's feeding it**. \\ +
-If the cam box fills with oil, it comes out the breather and right to your air cleaner. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?p=110375&highlight=variable+volume#post110375)) \\ +
-It's been a chronic issue on XL's for years, happens on the 5-speed bikes as well as the 4-speeds and the ironheads. \\ +
-But often on the head breather models (91-up), you never know like you do on earlier bikes with the breather on the cam box (pre 91). \\ +
-  * Wetsumping can also be attributed to the //Density// of the air / oil mix in the crankcase. ((Dr Dick of the XLFORUM http://xlforum.net/forums/showthread.php?t=1204854)) +
-  * The higher the density (//not volume//) of the fluid (air / oil mix), the more it drags on the rotating parts it contacts. +
-    * As the density increases so does the fluid drag it imposes on the rotating parts (read flywheel assembly). +
-    * This drag robs power. That's why we mess with it, to reduce the power loss. +
-  * Example: If they are the same size (volume), what takes less power? +
-    * Stirring a cup of coffee or stirring a coffee milkshake? It's the one that's less dense. +
-    * So now we know that less drag = more horsepower and the air is the medium that gets the oil out of the cases. \\ The 'leaner' (less oil in the air), the less the drag (air / oil is less dense). ((Dr Dick of the XLFORUM http://xlforum.net/forums/showthread.php?t=1204854&page=2)) +
- +
-The oil pump was updated in '98 and then in '07 and you rarely see this anymore (while putting around town). \\ +
-But it still happens on high rpm and race motors from time to time. \\ +
-It's always the best sealed motors that have the issue, especially gapless ring motors. \\ +
-Vacuum (45° configuration as mentioned above) in the crankcase interferes big time with scavenging. \\ +
-The 98-up style pump can be fitted to the older bikes (they've even been fitted to ironheads). \\ +
- +
-The late model bikes can easily wet sump if ridden aggressively on the street, however. ((maru of the XLFORUM http://xlforum.net/forums/showthread.php?t=75740&highlight=reed+valve&page=7)) \\ +
-And they've been known to wet sump with only 3 back to back dyno pulls. \\ +
-The results are dramatic when it happens. It is not anything like a barely noticeable loss in performance. \\ +
-The scavenging gets behind to some degree in a single drag strip run. \\ +
- +
-Beyond that, about all you can do is lower the oil pressure. \\ +
-But don't go down that path unless you establish for sure you are wetsumping and other measures won't fix the situation. \\ +
-Read more here on a [[techtalk:ref:oil05a|Homemade Oil System Bypass]] for reducing the oil pressure in the REF section of the Sportsterpedia. \\ +
-This mod will send a small amount of pressure side oil back to the tank instead of into the engine. \\ +
- +
  
 ====== Crankcase Pressure ====== ====== Crankcase Pressure ======
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   * [[techtalk:ref:engmech07f|Liquid Drag vs Fluid Drag]]   * [[techtalk:ref:engmech07f|Liquid Drag vs Fluid Drag]]
   * [[techtalk:ref:engmech04p|Vacuum Pump for Reducing Crankcase Pressure]]   * [[techtalk:ref:engmech04p|Vacuum Pump for Reducing Crankcase Pressure]]
-==== How crankcase pressure is generated ==== 
  
 +==== How crankcase pressure is generated ====
 Crankcase air pressure is mainly generated by the up and down movement of the pistons. \\ Crankcase air pressure is mainly generated by the up and down movement of the pistons. \\
 Additional air pressure is created by blowby from the combustion chambers past the rings and into the crankcase. \\ Additional air pressure is created by blowby from the combustion chambers past the rings and into the crankcase. \\
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 ==== The full crankcase pressure compartment ==== ==== The full crankcase pressure compartment ====
-  +Engine ventilation is connected to the rockerbox, crankcase, cam gear case and the oil tank. ((bunny32 of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-bottom-end/35356-install-new-crankcase-vent-04/page3?t=67658&page=3)) \\
-Engine ventilation is connected to the rockerbox, crankcase, cam gear case and the oil tank. ((bunny32 of the XLFORUM http://xlforum.net/forums/showthread.php?t=67658&page=3)) \\+
 If you blow down the oil tank line...air comes out the rockerbox vents (or cam breather hose). \\ If you blow down the oil tank line...air comes out the rockerbox vents (or cam breather hose). \\
 There are airways linking these compartments together and in looking at these airways. \\ There are airways linking these compartments together and in looking at these airways. \\
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 ==== Oil pump pressure isn't directly connected to crankcase pressure ==== ==== Oil pump pressure isn't directly connected to crankcase pressure ====
- 
 Secondary affects of pumping oil to the rocker boxes and rod bearings is the added oil in the bottom. \\ Secondary affects of pumping oil to the rocker boxes and rod bearings is the added oil in the bottom. \\
 Drain oil aids in splash lube and cooling features but if it's not removed fast enough, it creates thicker oil in suspension. \\ Drain oil aids in splash lube and cooling features but if it's not removed fast enough, it creates thicker oil in suspension. \\
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       * The pressure is increased at the pump as oil flows through more restrictions to get to these places. \\ (strictly as a non tested example, 10 psi on the feed side of the pump may equate to 4 psi or lower once it reaches the crankpin) \\ Pressure is restricted in the cam cover, \\ Less restricted with the wider opening at the pinion shaft bushing, \\ Then restricted again thru the shaft hole and the turns in the flywheel to the crankpin.       * The pressure is increased at the pump as oil flows through more restrictions to get to these places. \\ (strictly as a non tested example, 10 psi on the feed side of the pump may equate to 4 psi or lower once it reaches the crankpin) \\ Pressure is restricted in the cam cover, \\ Less restricted with the wider opening at the pinion shaft bushing, \\ Then restricted again thru the shaft hole and the turns in the flywheel to the crankpin.
     * Once the pressurized oil reaches the rocker arms and crankpin, the pressure is released into the wider openings in the oil path. \\ From there it is added to and becomes a part of crankcase pressure and is used and vented as such.     * Once the pressurized oil reaches the rocker arms and crankpin, the pressure is released into the wider openings in the oil path. \\ From there it is added to and becomes a part of crankcase pressure and is used and vented as such.
- 
  
 In contrast to the Sportster breather valve location, Buells breath through reed valves placed in the cam wall. \\ In contrast to the Sportster breather valve location, Buells breath through reed valves placed in the cam wall. \\
 **Buell crankcase breathing**: \\ **Buell crankcase breathing**: \\
-|  This is a Buell XBRR with reed valves through the cam chest wall. ((photos by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=829935))  ||+|  This is a Buell XBRR with reed valves through the cam chest wall. ((photos by aswracing of the XLFORUM https://www.xlforum.net/forum/buell-motorcycle-forum/buell-motorcycle-engine-conversions/97902-buell-xbrr-engine-build-pictures?t=829935))  ||
 |{{:techtalk:ref:engmech:reed_valves_1_on_buell_xbrr_by_aswracing.jpg?direct&300|}}|{{:techtalk:ref:engmech:reed_valves_2_on_buell_xbrr_by_aswracing.jpg?direct&300|}}| |{{:techtalk:ref:engmech:reed_valves_1_on_buell_xbrr_by_aswracing.jpg?direct&300|}}|{{:techtalk:ref:engmech:reed_valves_2_on_buell_xbrr_by_aswracing.jpg?direct&300|}}|
- 
  
 ==== The pressure in the crankcase is not from oil pump pressure ==== ==== The pressure in the crankcase is not from oil pump pressure ====
- 
 Static oil pump pressure has already been dissipated by the time it reaches the crankcase. \\ Static oil pump pressure has already been dissipated by the time it reaches the crankcase. \\
 (although it takes static oil pressure to get the oil from the pump to the crankcase) \\ (although it takes static oil pressure to get the oil from the pump to the crankcase) \\
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 ==== Role of the breather valve ==== ==== Role of the breather valve ====
- 
 CC pressure both pushes to and sucks from the breather valve. \\ CC pressure both pushes to and sucks from the breather valve. \\
 The breather valve allows for controlled air pressure to both leave and enter the engine to obtain what is referred to as a "slight running vacuum" in the crankcase. \\ The breather valve allows for controlled air pressure to both leave and enter the engine to obtain what is referred to as a "slight running vacuum" in the crankcase. \\
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 ==== Oil Tank's Role vs Wetsumping ==== ==== Oil Tank's Role vs Wetsumping ====
- 
 See the full article,   * [[techtalk:ref:oil20|Oil Tank Pressure]], in the REF section of the Sportsterpedia. \\ See the full article,   * [[techtalk:ref:oil20|Oil Tank Pressure]], in the REF section of the Sportsterpedia. \\
 There should not be any pressure difference in the oil tank than the engine although it does transfer pressure. \\ There should not be any pressure difference in the oil tank than the engine although it does transfer pressure. \\
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 So if you have pressure in your oil tank and the vent to the cam chest is not blocked then the cam chest is also pressurized. \\ So if you have pressure in your oil tank and the vent to the cam chest is not blocked then the cam chest is also pressurized. \\
 If the cam chest is holding pressure, then your breather valve can not be venting properly. \\ If the cam chest is holding pressure, then your breather valve can not be venting properly. \\
-Bottom line is that if the vent system is working properly, you shouldn't have excessive pressure build up in the oil tank. ((Deimus of the XLFORUM http://xlforum.net/forums/showthread.php?t=87313)) \\+Bottom line is that if the vent system is working properly, you shouldn't have excessive pressure build up in the oil tank. ((Deimus of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-suspension-frame-forks-handlebars-fuel-tank-oil-tank-fenders/40457-whoa-oil-tank-vomits-oil?t=87313)) \\
  
 ==== Lowering the oil level in the oil tank ==== ==== Lowering the oil level in the oil tank ====
- 
 It has been said by many that lowering the oil level in the oil tank will stop oil puking out the breather. \\ It has been said by many that lowering the oil level in the oil tank will stop oil puking out the breather. \\
 While this may work in application, by design, you should not have to lower the oil level. \\ While this may work in application, by design, you should not have to lower the oil level. \\
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 ==== Affects of the 45° Rod / Piston Arrangement ==== ==== Affects of the 45° Rod / Piston Arrangement ====
- 
 Since Sportster piston movement is not equalized, we get the potato, potato sound we all love but the equilibrium in the crankcase is off by design. \\ Since Sportster piston movement is not equalized, we get the potato, potato sound we all love but the equilibrium in the crankcase is off by design. \\
 This constant push / pull from offset pistons contributes to an imbalance of pressure that needs to controlled. \\  This constant push / pull from offset pistons contributes to an imbalance of pressure that needs to controlled. \\ 
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 ==== Differential Pressure (vacuum and air pressure) ==== ==== Differential Pressure (vacuum and air pressure) ====
- +Vacuum and (positive) air pressure are the terms that describe the amount of molecules of a gas in a given unit of space. ((Dr Dick of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/122424-breather-diagrams/page4?t=1204854&page=4)) \\
-Vacuum and (positive) air pressure are the terms that describe the amount of molecules of a gas in a given unit of space. ((Dr Dick of the XLFORUM http://xlforum.net/forums/showthread.php?t=1204854&page=4)) \\+
 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: \\
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 A vacuum condition when downstroke begins lessens the restriction on the descending pistons and doesn't lower overall horsepower. \\ A vacuum condition when downstroke begins lessens the restriction on the descending pistons and doesn't lower overall horsepower. \\
  
-In most engines negative crankcase pressure allows less ring pressure and the combination of both means more hp. ((maru of the XLFORUM http://xlforum.net/forums/showthread.php?t=75740&highlight=reed+valve&page=8)) \\+In most engines negative crankcase pressure allows less ring pressure and the combination of both means more hp. ((maru of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-engine-conversions/38153-xr750-883-series-race-engine-venting-etc/page8?t=75740&highlight=reed+valve&page=8)) \\
 Over the years folks have used exhaust system energy to pull pressure from the case for this reason. \\ Over the years folks have used exhaust system energy to pull pressure from the case for this reason. \\
 Guys have won championships with an engine that had an electric vacuum pump to reduce (positive) crankcase air pressure. \\ Guys have won championships with an engine that had an electric vacuum pump to reduce (positive) crankcase air pressure. \\
-Crankcase pressure in these engines fluctuate wildly from positive to negative. ((maru of the XLFORUM http://xlforum.net/forums/showthread.php?t=75740&highlight=reed+valve&page=8)) \\+Crankcase pressure in these engines fluctuate wildly from positive to negative. ((maru of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-engine-conversions/38153-xr750-883-series-race-engine-venting-etc/page8?t=75740&highlight=reed+valve&page=8)) \\
 However, high vacuum can have a dramatic affect on scavenging. \\ However, high vacuum can have a dramatic affect on scavenging. \\
  
 __See, Differential Pressure, in the sub documents at the top of this page for more information__. \\ __See, Differential Pressure, in the sub documents at the top of this page for more information__. \\
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 ==== Symptoms of High Crankcase Pressure ==== ==== Symptoms of High Crankcase Pressure ====
- 
 Picture a balloon inside the engine being blown up. \\ Picture a balloon inside the engine being blown up. \\
 It puts internal pressure against the weakest structural points (gaskets and seals). \\ It puts internal pressure against the weakest structural points (gaskets and seals). \\
  
-Symptoms include: ((Jorgen of the XLFORUM http://xlforum.net/forums/showthread.php?t=75740&highlight=reed+valve&page=9)) \\+Symptoms include: ((Jorgen of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-engine-conversions/38153-xr750-883-series-race-engine-venting-etc/page9?t=75740&highlight=reed+valve&page=9)) \\
 Sweating oil from the cylinder base gaskets and rocker boxes. \\ Sweating oil from the cylinder base gaskets and rocker boxes. \\
 As well as the push rod tubes and lifter blocs on the other side. \\ As well as the push rod tubes and lifter blocs on the other side. \\
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 ==== Blowby ==== ==== Blowby ====
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 Normal blowby: \\ Normal blowby: \\
-In the absence of any blow-by getting past the rings, the crankcase alternates from atmospheric (pistons down) to a vacuum (pistons up). ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=15705&page=2)) \\+In the absence of any blow-by getting past the rings, the crankcase alternates from atmospheric (pistons down) to a vacuum (pistons up). ((aswracing of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/10013-blowby-article/page2?t=15705&page=2)) \\
 But in the real world, a little gets past the rings, so there's a net outflow equal to that. \\ But in the real world, a little gets past the rings, so there's a net outflow equal to that. \\
-Conventional rings have a ring gap and the combustion pressure is very great. ((Deimus of the XLFORUM http://xlforum.net/forums/showthread.php?t=67658&page=3)) \\+Conventional rings have a ring gap and the combustion pressure is very great. ((Deimus of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-bottom-end/35356-install-new-crankcase-vent-04/page3?t=67658&page=3)) \\
 So you can bet some of this tremendous pressure is entering into your crankcase instead of 100% of it exiting your exhaust pipes.  So you can bet some of this tremendous pressure is entering into your crankcase instead of 100% of it exiting your exhaust pipes. 
  
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 ==== What causes extra air in the crankcase (air leaks)? ==== ==== What causes extra air in the crankcase (air leaks)? ====
- 
 Ring seal, as mentioned, is not as good on higher RPM even on a healthy engine. \\ Ring seal, as mentioned, is not as good on higher RPM even on a healthy engine. \\
  
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 ==== Why is the ratio of positive and negative pressure important? ==== ==== Why is the ratio of positive and negative pressure important? ====
- 
 It takes a balance of the two to run a Sportster engine. \\ It takes a balance of the two to run a Sportster engine. \\
- 
 Piston upstroke creates negative pressure and suction of oil from the sump. \\ Piston upstroke creates negative pressure and suction of oil from the sump. \\
 It pulls oil up in the form of oil mist to be tossed around on the moving metal parts. \\ It pulls oil up in the form of oil mist to be tossed around on the moving metal parts. \\
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 So the internal pressure is more stable until extra air (or blowby) is induced into the crankcase. \\ So the internal pressure is more stable until extra air (or blowby) is induced into the crankcase. \\
  
-|  Testing CC pressure on the dyno. ((photo by Jörgen http://xlforum.net/forums/showthread.php?t=75740&page=9))  |+|  Testing CC pressure on the dyno. ((photo by Jörgen https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-engine-conversions/38153-xr750-883-series-race-engine-venting-etc/page9?t=75740&page=9))  |
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Trace: • REF: Engine Mechanicals