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techtalk:ref:engmech04 [2020/10/07 03:21]
hippysmack [Symptoms of Breather Valve Problems]
techtalk:ref:engmech04 [2023/12/22 20:25] (current)
hippysmack [Symptoms of High Crankcase Pressure]
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 ====== 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. \\ 
-  ​+ 
 +{{:​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 ==== ==== 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]]
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 ==== Symptoms of Breather Valve Problems ==== ==== Symptoms of Breather Valve Problems ====
- 
 **The most notable signs of breather valve problems include weeping / leaking gaskets or blown gaskets / seals**. \\ **The most notable signs of breather valve problems include weeping / leaking gaskets or blown gaskets / seals**. \\
 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. \\ 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. \\
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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. \\
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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__. \\
- 
  
 ==== 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. \\
- 
  
 ==== Blowby ==== ==== Blowby ====
- 
 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)) ​ |
 |{{:​techtalk:​ref:​engmech:​testing_crankcase_pressure_on_the_dyno_by_jorgen.jpg?​direct&​300|}}| |{{:​techtalk:​ref:​engmech:​testing_crankcase_pressure_on_the_dyno_by_jorgen.jpg?​direct&​300|}}|
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