Really good explanation for Oil-Blow-By
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Road Master
Joined: Mar 2018
Posts: 804
Likes: 92
From: Texas
Really good explanation for Oil-Blow-By
S&S says it has determined the problem to be the continuous rise and fall of the air pressure in the crankcase, cam chest and rocker boxes. That the pressure changes are caused by large volume of air moving in and out of the crankcase as the pistons travel up and down. As a result of this air flow and the changes in pressure in the cam chest, air also flows in and out of the rocker boxes through the cylinder head oil drain passages. At sustained high speeds the constant in and out flow of air in the rocker boxes interrupts the free flow of oil from the cylinder heads to the cam chest . In fact a small quantity of oil, pushed up and down by the pressure changes, is trapped in the drain passage, effectively blocking the passage so that no oil can drain out of the rocker boxes . When enough oil has accumulated in the rocker boxes, it will start to blow out the breather passage to the air cleaner and ends up all over your bike, your passengers new boots, and in extreme cases on your rear tire .
Reason for Oil Blow By: More air is displaced by the ascending and descending pistons when a 95" and larger kits have been installed, simply because there's bigger pistons moving up and down. Sustained high rpm riding aggravates blow by because more oil is being pumped into the engine since the pump is turning faster. The rocker boxes become overwhelmed with too much oil that it cannot separate the oil from the escaping air. Some stock displacement engines have oil blow-by problems even when ridden moderately, but that is not the norm. Blow-by does not happen immediately because the oil buildup that causes it takes time to occur. That's why blow-by sometimes doesn't occur until after sustained high-speed riding.
From Nov 04 issue of American Iron - Donnie Smith:
The breather system is all about separating gaseous materials from the oil to allow the engine to vent to the atmosphere without puking oil all over its exterior. The engine must vent the pressure built up in the crankcase by the ascending and descending pistons. As the pistons descend in both cylinders, which happens on the power and intake strokes, the air in the flywheel compartment (crankcase), which is below the pistons, is pressurized because there's less space under the pistons for the air to occupy. The thrashing flywheel assembly also produces a fine oil mist that combines with the air in the crankcase. This oily, pressurized air must be allowed to escape, or it will soon blow out the engine's gaskets and seals. This oily, pressurized air is forced (vented) out of the crankcase, through the spaces between the bearings and races of the pinion bearing, and into the gear case compartment. It is then allowed to go up the pushrod tubes and into the rocker boxes. Once in the two rocker boxes, the oily, pressurized air rushes under the rocker arm support plates and into openings that lead to the breather baffle assemblies - there's one in each rocker box.
The first advantage to making the oily pressurized air go up the pushrod tubes is that gravity assists in separating the heavier oil from the lighter pressurized air, but the separation process needs more help than that.
There is a three-stage system in the rocker boxes for venting the displaced air back into the combustion chamber, where any oil residue is burned off to prevent all but a minimum of emissions from escaping to the atmosphere.
The three-stage system consists of an open-cell foam disc, which can be described as an oil filter gauze element. This open-cell foam disc, which is shaped like a 1" long barrel, scrubs oil from the oil air vapor. The disc is very porous and air is easily blown through the foam.
The oil that gets separated from the air flows through two small return holes in the rocker arm support plate to return to the gear case - unless there's too much oil to deal with!! The cleansed air is then fed through an umbrella flapper valve (the 2nd stage), which rises to let the air through. This flapper valves an umbrella-shaped, one-way, rubber valve that lets air out of the engine, but will not allow it to come back in. Once the piston begins to ascend, pressure in the crankcase drops, and the air in the breather compartment reverses direction. When this happens, the flaps of the umbrella valve drop down, sealing the vent hole and blocking the cleansed air from returning. But when overwhelmed will let oil out of the engine along with the air. The cleansed air then follows a tortuous path in the rocker boxes (3rd stage), which allows air to escape, but separates any residual oil from the air. (Tortuous is the term used by engineers to describe a channel that gases find easy to follow, but liquids do not.) After the oil is separated and the gases flow out of the heads, the gasses are sucked back into the carb, or EFI venturi , and into the combustion chamber to be burned.
https://www.cvoharley.com/smf/index.php?topic=14309.0
Reason for Oil Blow By: More air is displaced by the ascending and descending pistons when a 95" and larger kits have been installed, simply because there's bigger pistons moving up and down. Sustained high rpm riding aggravates blow by because more oil is being pumped into the engine since the pump is turning faster. The rocker boxes become overwhelmed with too much oil that it cannot separate the oil from the escaping air. Some stock displacement engines have oil blow-by problems even when ridden moderately, but that is not the norm. Blow-by does not happen immediately because the oil buildup that causes it takes time to occur. That's why blow-by sometimes doesn't occur until after sustained high-speed riding.
From Nov 04 issue of American Iron - Donnie Smith:
The breather system is all about separating gaseous materials from the oil to allow the engine to vent to the atmosphere without puking oil all over its exterior. The engine must vent the pressure built up in the crankcase by the ascending and descending pistons. As the pistons descend in both cylinders, which happens on the power and intake strokes, the air in the flywheel compartment (crankcase), which is below the pistons, is pressurized because there's less space under the pistons for the air to occupy. The thrashing flywheel assembly also produces a fine oil mist that combines with the air in the crankcase. This oily, pressurized air must be allowed to escape, or it will soon blow out the engine's gaskets and seals. This oily, pressurized air is forced (vented) out of the crankcase, through the spaces between the bearings and races of the pinion bearing, and into the gear case compartment. It is then allowed to go up the pushrod tubes and into the rocker boxes. Once in the two rocker boxes, the oily, pressurized air rushes under the rocker arm support plates and into openings that lead to the breather baffle assemblies - there's one in each rocker box.
The first advantage to making the oily pressurized air go up the pushrod tubes is that gravity assists in separating the heavier oil from the lighter pressurized air, but the separation process needs more help than that.
There is a three-stage system in the rocker boxes for venting the displaced air back into the combustion chamber, where any oil residue is burned off to prevent all but a minimum of emissions from escaping to the atmosphere.
The three-stage system consists of an open-cell foam disc, which can be described as an oil filter gauze element. This open-cell foam disc, which is shaped like a 1" long barrel, scrubs oil from the oil air vapor. The disc is very porous and air is easily blown through the foam.
The oil that gets separated from the air flows through two small return holes in the rocker arm support plate to return to the gear case - unless there's too much oil to deal with!! The cleansed air is then fed through an umbrella flapper valve (the 2nd stage), which rises to let the air through. This flapper valves an umbrella-shaped, one-way, rubber valve that lets air out of the engine, but will not allow it to come back in. Once the piston begins to ascend, pressure in the crankcase drops, and the air in the breather compartment reverses direction. When this happens, the flaps of the umbrella valve drop down, sealing the vent hole and blocking the cleansed air from returning. But when overwhelmed will let oil out of the engine along with the air. The cleansed air then follows a tortuous path in the rocker boxes (3rd stage), which allows air to escape, but separates any residual oil from the air. (Tortuous is the term used by engineers to describe a channel that gases find easy to follow, but liquids do not.) After the oil is separated and the gases flow out of the heads, the gasses are sucked back into the carb, or EFI venturi , and into the combustion chamber to be burned.
https://www.cvoharley.com/smf/index.php?topic=14309.0
Thread Starter
|
Road Master
Joined: Mar 2018
Posts: 804
Likes: 92
From: Texas
S&S says it has determined the problem to be the continuous rise and fall of the air pressure in the crankcase, cam chest and rocker boxes. That the pressure changes are caused by large volume of air moving in and out of the crankcase as the pistons travel up and down. As a result of this air flow and the changes in pressure in the cam chest, air also flows in and out of the rocker boxes through the cylinder head oil drain passages. At sustained high speeds the constant in and out flow of air in the rocker boxes interrupts the free flow of oil from the cylinder heads to the cam chest . In fact a small quantity of oil, pushed up and down by the pressure changes, is trapped in the drain passage, effectively blocking the passage so that no oil can drain out of the rocker boxes . When enough oil has accumulated in the rocker boxes, it will start to blow out the breather passage to the air cleaner and ends up all over your bike, your passengers new boots, and in extreme cases on your rear tire .
Reason for Oil Blow By: More air is displaced by the ascending and descending pistons when a 95" and larger kits have been installed, simply because there's bigger pistons moving up and down. Sustained high rpm riding aggravates blow by because more oil is being pumped into the engine since the pump is turning faster. The rocker boxes become overwhelmed with too much oil that it cannot separate the oil from the escaping air. Some stock displacement engines have oil blow-by problems even when ridden moderately, but that is not the norm. Blow-by does not happen immediately because the oil buildup that causes it takes time to occur. That's why blow-by sometimes doesn't occur until after sustained high-speed riding.
From Nov 04 issue of American Iron - Donnie Smith:
The breather system is all about separating gaseous materials from the oil to allow the engine to vent to the atmosphere without puking oil all over its exterior. The engine must vent the pressure built up in the crankcase by the ascending and descending pistons. As the pistons descend in both cylinders, which happens on the power and intake strokes, the air in the flywheel compartment (crankcase), which is below the pistons, is pressurized because there's less space under the pistons for the air to occupy. The thrashing flywheel assembly also produces a fine oil mist that combines with the air in the crankcase. This oily, pressurized air must be allowed to escape, or it will soon blow out the engine's gaskets and seals. This oily, pressurized air is forced (vented) out of the crankcase, through the spaces between the bearings and races of the pinion bearing, and into the gear case compartment. It is then allowed to go up the pushrod tubes and into the rocker boxes. Once in the two rocker boxes, the oily, pressurized air rushes under the rocker arm support plates and into openings that lead to the breather baffle assemblies - there's one in each rocker box.
The first advantage to making the oily pressurized air go up the pushrod tubes is that gravity assists in separating the heavier oil from the lighter pressurized air, but the separation process needs more help than that.
There is a three-stage system in the rocker boxes for venting the displaced air back into the combustion chamber, where any oil residue is burned off to prevent all but a minimum of emissions from escaping to the atmosphere.
The three-stage system consists of an open-cell foam disc, which can be described as an oil filter gauze element. This open-cell foam disc, which is shaped like a 1" long barrel, scrubs oil from the oil air vapor. The disc is very porous and air is easily blown through the foam.
The oil that gets separated from the air flows through two small return holes in the rocker arm support plate to return to the gear case - unless there's too much oil to deal with!! The cleansed air is then fed through an umbrella flapper valve (the 2nd stage), which rises to let the air through. This flapper valves an umbrella-shaped, one-way, rubber valve that lets air out of the engine, but will not allow it to come back in. Once the piston begins to ascend, pressure in the crankcase drops, and the air in the breather compartment reverses direction. When this happens, the flaps of the umbrella valve drop down, sealing the vent hole and blocking the cleansed air from returning. But when overwhelmed will let oil out of the engine along with the air. The cleansed air then follows a tortuous path in the rocker boxes (3rd stage), which allows air to escape, but separates any residual oil from the air. (Tortuous is the term used by engineers to describe a channel that gases find easy to follow, but liquids do not.) After the oil is separated and the gases flow out of the heads, the gasses are sucked back into the carb, or EFI venturi , and into the combustion chamber to be burned.
https://www.cvoharley.com/smf/index.php?topic=14309.0
Reason for Oil Blow By: More air is displaced by the ascending and descending pistons when a 95" and larger kits have been installed, simply because there's bigger pistons moving up and down. Sustained high rpm riding aggravates blow by because more oil is being pumped into the engine since the pump is turning faster. The rocker boxes become overwhelmed with too much oil that it cannot separate the oil from the escaping air. Some stock displacement engines have oil blow-by problems even when ridden moderately, but that is not the norm. Blow-by does not happen immediately because the oil buildup that causes it takes time to occur. That's why blow-by sometimes doesn't occur until after sustained high-speed riding.
From Nov 04 issue of American Iron - Donnie Smith:
The breather system is all about separating gaseous materials from the oil to allow the engine to vent to the atmosphere without puking oil all over its exterior. The engine must vent the pressure built up in the crankcase by the ascending and descending pistons. As the pistons descend in both cylinders, which happens on the power and intake strokes, the air in the flywheel compartment (crankcase), which is below the pistons, is pressurized because there's less space under the pistons for the air to occupy. The thrashing flywheel assembly also produces a fine oil mist that combines with the air in the crankcase. This oily, pressurized air must be allowed to escape, or it will soon blow out the engine's gaskets and seals. This oily, pressurized air is forced (vented) out of the crankcase, through the spaces between the bearings and races of the pinion bearing, and into the gear case compartment. It is then allowed to go up the pushrod tubes and into the rocker boxes. Once in the two rocker boxes, the oily, pressurized air rushes under the rocker arm support plates and into openings that lead to the breather baffle assemblies - there's one in each rocker box.
The first advantage to making the oily pressurized air go up the pushrod tubes is that gravity assists in separating the heavier oil from the lighter pressurized air, but the separation process needs more help than that.
There is a three-stage system in the rocker boxes for venting the displaced air back into the combustion chamber, where any oil residue is burned off to prevent all but a minimum of emissions from escaping to the atmosphere.
The three-stage system consists of an open-cell foam disc, which can be described as an oil filter gauze element. This open-cell foam disc, which is shaped like a 1" long barrel, scrubs oil from the oil air vapor. The disc is very porous and air is easily blown through the foam.
The oil that gets separated from the air flows through two small return holes in the rocker arm support plate to return to the gear case - unless there's too much oil to deal with!! The cleansed air is then fed through an umbrella flapper valve (the 2nd stage), which rises to let the air through. This flapper valves an umbrella-shaped, one-way, rubber valve that lets air out of the engine, but will not allow it to come back in. Once the piston begins to ascend, pressure in the crankcase drops, and the air in the breather compartment reverses direction. When this happens, the flaps of the umbrella valve drop down, sealing the vent hole and blocking the cleansed air from returning. But when overwhelmed will let oil out of the engine along with the air. The cleansed air then follows a tortuous path in the rocker boxes (3rd stage), which allows air to escape, but separates any residual oil from the air. (Tortuous is the term used by engineers to describe a channel that gases find easy to follow, but liquids do not.) After the oil is separated and the gases flow out of the heads, the gasses are sucked back into the carb, or EFI venturi , and into the combustion chamber to be burned.
https://www.cvoharley.com/smf/index.php?topic=14309.0
http://www.bikerrogue.com/Articles/T...m_Breather.htm
Trask Performance also makes "mystfree breathers"
https://traskperformance.com/product...twin-cam-kits/
Seasoned HDF Member
Joined: Oct 2014
Posts: 5,022
Likes: 2,352
From: Camp Lejeune, NC
Just pulled my plugs after 20k miles running the stock breather setup. They look exactly like yours.
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