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techtalk:ref:engmech07 [2020/10/09 00:54] hippysmack [Sub Documents] |
techtalk:ref:engmech07 [2023/12/26 19:55] (current) hippysmack |
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| ====== Engine Breathing ====== | ====== Engine Breathing ====== | ||
| - | + | 1957-1976 engines have a different breathing cycle than 1977-up engines. The end result is the same. However, the means to get there is different. \\ | |
| - | 57-76 engines have a different breathing cycle than 77-up engines. The end result is the same. However, the means to get there is different. \\ | + | |
| Below are the two systems explained. \\ | Below are the two systems explained. \\ | ||
| You can also reference the sub documents under each particle subject heading. These pages are more detailed information on certain subjects. \\ | You can also reference the sub documents under each particle subject heading. These pages are more detailed information on certain subjects. \\ | ||
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| * [[techtalk:ref:engmech07l|How Piston Swept Volume Compares When the Breather Opens as to When It Closes]] | * [[techtalk:ref:engmech07l|How Piston Swept Volume Compares When the Breather Opens as to When It Closes]] | ||
| - | <blockquote>The shallow sump, timed breather system, comes from the aviation world of old. ((mrmom9r of the XLFORUM http://xlforum.net/forums/showthread.php?t=1204854&page=4)) \\ | + | <blockquote>The shallow sump, timed breather system, comes from the aviation world of old. ((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)) \\ |
| Piston driven aircraft had to be able to evacuate the oil from the crankcase regardless of engine altitude and that system does that. \\ | Piston driven aircraft had to be able to evacuate the oil from the crankcase regardless of engine altitude and that system does that. \\ | ||
| At the time Harley adapted that system they were copying the highest engine technology of the day. \\ | At the time Harley adapted that system they were copying the highest engine technology of the day. \\ | ||
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| The oil is separated from the air by way of collision. Everything the air/oil mix touches on the way to the vent separates some oil from the air. | The oil is separated from the air by way of collision. Everything the air/oil mix touches on the way to the vent separates some oil from the air. | ||
| - | 57-76 engines breath and scavenge oil from the same hole. \\ | + | 1957-1976 engines breath and scavenge oil from the same hole. \\ |
| On piston down stroke, drain oil is pushed into the oil galley (slot) in the rear of the crankcase and toward the oil trap beside the breather gear. \\ | On piston down stroke, drain oil is pushed into the oil galley (slot) in the rear of the crankcase and toward the oil trap beside the breather gear. \\ | ||
| - | When the breather window opens, both drain oil and crankcase air pressure are pushed into the rotating breather gear. \\ | + | When the breather window opens after downstroke, both drain oil and crankcase air pressure are pushed into the rotating breather gear. \\ |
| The oil and air is slung out from the center of the gear into the gearcase where it bounces on cam gears, case walls, etc. \\ | The oil and air is slung out from the center of the gear into the gearcase where it bounces on cam gears, case walls, etc. \\ | ||
| - | Air / oil mist flows toward the vent and the oil gets spun out of suspension by the oil slinger. \\ | + | Air / oil mist flows toward the vent and the oil gets spun out of suspension by the oil slinger on the generator drive gear. \\ |
| - | + | Crankcase exhaust air is then sent out the breather tube. \\ | |
| - | The breather valve then closes on piston upstroke past BDC, creating vacuum in the crankcase. \\ | + | The breather valve then closes on after the pistons rise (after BDC), creating vacuum in the crankcase and the cycle repeats. \\ |
| - | Crankcase exhaust air from the gearcase is sent out the breather tube. \\ | + | |
| - | Any oil still in suspension with the air on the way to the breather tube is separated by an oil slinger on the generator drive gear. \\ | + | |
| ===== 1977-1985 ===== | ===== 1977-1985 ===== | ||
| - | + | 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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| Many cases of excess breather oil is caused by poorly functioning check valves. | Many cases of excess breather oil is caused by poorly functioning check valves. | ||
| - | **Engine Breathing Cycle**: \\ | + | **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. \\ | + | Upstroke pulls this mixture up into suspension but in tiny particles to mix with the air moving around and thrown here to there for lubrication. \\ |
| The oil is separated from the air by way of collision. Everything the air/oil mix touches on the way to the vent separates some oil from the air. \\ | The oil is separated from the air by way of collision. Everything the air/oil mix touches on the way to the vent separates some oil from the air. \\ | ||
| - | 77-up engines blow the air/oil mix into the gearcase where it bounces on cam gears, case walls, etc. and then gets spun out by the oil slinger. \\ | + | |
| - | This helps to splash lube the moving parts in the engine when it is picked up and blown around. \\ | + | 1977-up engines scavenge oil from down low in the crankcase and breath up higher through holes in the cam wall. \\ |
| - | The oil mist is then separated from the crankcase air and the excess air pressure is vented out of the engine past the one way breather valve. \\ | + | On piston downstroke, drain oil is pushed into the oil galley and crankcase air pressure is pushed into the gearcase and the breather valve is pushed open. \\ |
| - | 77-85 engines vent through a valve in the cam cover. \\ | + | The air/ oil mist is slung around in the gearcase where it bounces on cam gears, case walls, etc. \\ |
| + | Remaining air / oil mist flows toward the vent. \\ | ||
| + | On 1977-E1984 engines, oil gets spun out of suspension by the oil slinger on the generator drive gear and crankcase exhaust air is then sent out the breather vent. \\ | ||
| + | On L84-85 engines, the slinger washer was removed and a breather baffle tube was installed in the cover to separate oil. \\ | ||
| + | Oil hits the breather baffler tube then the back side of the breather valve to separate from the air and drains back into the gearcase. \\ | ||
| + | The breather valve then closes at piston (BDC), creating vacuum in the crankcase as the piston rises and the cycle repeats. \\ | ||
| There were several changes made of the valve itself, but they operate on the same principle as a one way breather valve. \\ | There were several changes made of the valve itself, but they operate on the same principle as a one way breather valve. \\ | ||
| + | |||
| + | ==== OEM oil paths and engine breathing drawings ==== | ||
| + | |||
| + | {{:techtalk:ref:engmech:1957-1971_sportster_crankcase_pressure_path_by_hippysmack.png?direct&500|}} ((drawing by Hippysmack)) \\ | ||
| + | |||
| + | {{:techtalk:ref:engmech:1972-1976_sportster_crankcase_pressure_path_by_hippysmack.png?direct&750|}} ((drawing by Hippysmack)) \\ | ||
| + | |||
| + | {{:techtalk:ref:engmech:1977-1985_sportster_crankcase_pressure_path_by_hippysmack.png?direct&500|}} ((drawing by Hippysmack)) \\ | ||
| ====== Engine Breather Valves ====== | ====== Engine Breather Valves ====== | ||
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| * [[techtalk:ref:engmech07h|Oil Drainback and Supplemental Air Intake from Breather Valves]] | * [[techtalk:ref:engmech07h|Oil Drainback and Supplemental Air Intake from Breather Valves]] | ||
| * [[techtalk:ref:engmech07i|Dissecting the 77-78 Breather (foo-foo) Valve (24634-77)]] | * [[techtalk:ref:engmech07i|Dissecting the 77-78 Breather (foo-foo) Valve (24634-77)]] | ||
| + | * [[techtalk:ref:engmech07j|Further Study of the 79-E82 Reed Valve]] | ||
| * [[techtalk:ref:engmech07s|XR-750 8-Ball Breather Valve]] | * [[techtalk:ref:engmech07s|XR-750 8-Ball Breather Valve]] | ||
| * [[techtalk:ref:engmech05|Breather Venting / Relocation]] (list of breathing mods and aftermarket breathers for 1977-up engines) | * [[techtalk:ref:engmech05|Breather Venting / Relocation]] (list of breathing mods and aftermarket breathers for 1977-up engines) | ||
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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**. \\ | ||
| - | 77-E82 breather valves can get drudged in old thickened oil and not open/close properly. \\ | + | 1977-E1982 breather valves can get drudged in old thickened oil and not open/close properly. \\ |
| - | 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. \\ | + | L1982-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. \\ |
| Stopped up breather valves won't allow the engine to breath well and can create excess vacuum and implode gaskets. \\ | Stopped up breather valves won't allow the engine to breath well and can create excess vacuum and implode 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. \\ | ||
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| * [[techtalk:ref:engmech07b|Affects of the 45° Rod / Piston Arrangement]] | * [[techtalk:ref:engmech07b|Affects of the 45° Rod / Piston Arrangement]] | ||
| * [[techtalk:ref:engmech07c|Differential Pressure]] | * [[techtalk:ref:engmech07c|Differential Pressure]] | ||
| + | * [[techtalk:ref:engmech04r|Air Pressure and Vacuum at Different Elevations]] | ||
| * [[techtalk:ref:engmech07d|Blowby and Ring Seal]] | * [[techtalk:ref:engmech07d|Blowby and Ring Seal]] | ||
| * [[techtalk:ref:engmech07f|Liquid Drag vs Fluid Drag]] | * [[techtalk:ref:engmech07f|Liquid Drag vs Fluid Drag]] | ||
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| * [[techtalk:ref:oil20|Oil Tank Pressure]] | * [[techtalk:ref:oil20|Oil Tank Pressure]] | ||
| * [[techtalk:ref:engmech04p|Vacuum Pump for Reducing Crankcase Pressure]] | * [[techtalk:ref:engmech04p|Vacuum Pump for Reducing Crankcase Pressure]] | ||
| + | * See also in the Sportsterpedia: | ||
| + | * [[techtalk:ih:oil01#transfer_valve_76_and_earlier|Transfer Valve]] | ||
| + | |||
| ==== In the crankcase air system ==== | ==== In the crankcase air system ==== | ||
| - | |||
| 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 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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| ==== 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. \\ | ||
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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? ==== | ==== What causes extra air in the crankcase? ==== | ||
| - | |||
| 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. \\ | ||
| Gasket / air leaks can introduce more air in the crankcase. \\ | Gasket / air leaks can introduce more air in the crankcase. \\ | ||
