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techtalk:ref:engmech05i [2020/09/22 23:47] hippysmack [79-85 Breather Vent Mod - Adding a Secondary Vent Hose at 6:00 Position] |
techtalk:ref:engmech05i [2020/10/08 15:18] hippysmack [79-85 Breather Vent Mod - Adding a Secondary Vent Hose at 6:00 Position] |
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| * Older bikes were originally plumbed into the A/C from a vent in the 6:00 position with a metal tube as a vent dumping to atmosphere. ((doodah man of the XLFORUM http://xlforum.net/forums/showthread.php?p=5786300)) \\ It would mist a small amount of oil while riding but not a major oil slick. | * Older bikes were originally plumbed into the A/C from a vent in the 6:00 position with a metal tube as a vent dumping to atmosphere. ((doodah man of the XLFORUM http://xlforum.net/forums/showthread.php?p=5786300)) \\ It would mist a small amount of oil while riding but not a major oil slick. | ||
| * 79-up Ironheads can benefit from removing the 6 o'clock plug from the cover and adding an additional breather hose there. \\ It is said to allow the crankcase pressure to evacuate faster, resulting in the motor being a little more free-revving. \\ A side benefit is that it will largely eliminate the "oil in the air cleaner" syndrome, assuming the original breather is left in place. \\ You can terminate the extra breather hose under the engine. However, it will drip a spot or two of oil there when parked or after a "spirited" ride. | * 79-up Ironheads can benefit from removing the 6 o'clock plug from the cover and adding an additional breather hose there. \\ It is said to allow the crankcase pressure to evacuate faster, resulting in the motor being a little more free-revving. \\ A side benefit is that it will largely eliminate the "oil in the air cleaner" syndrome, assuming the original breather is left in place. \\ You can terminate the extra breather hose under the engine. However, it will drip a spot or two of oil there when parked or after a "spirited" ride. | ||
| - | * In the pic below, you can see where the oil normally drains back into the engine. \\ Air and oil mist (oil that gets past the oil slinger on the generator) gets blown into the red valve. \\ In the cavity behind the reed, oil drops out of suspension and drains back. \\ At the same time, the air is purged out the vent hose. | + | * In the pic below, you can see where the oil normally drains back into the engine. \\ Air and oil mist (oil that gets past the oil slinger on the generator) gets blown into the reed valve. \\ In the cavity behind the reed, oil drops out of suspension and drains back. \\ At the same time, the air is purged out the vent hose. |
| * **Considerations**: | * **Considerations**: | ||
| - | * With the cam cover off, you can see a tiny hole drilled at the bottom of the cavity that by-passes the breather vent. \\ This hole drains separated oil that collects in the cavity back into the motor. \\ Be aware that opening the bottom port in the breather can affect the oil drain-back feature. \\ A hose connected to that position can still dribble oil out in small droplets from time to time. \\ If the motor is pushing oil out the breather, you may have a ring seal or other problem. \\ Adding a second breather hose will not fix that. | + | * With the cam cover off, you can see a tiny hole drilled at the bottom of the cavity that by-passes the breather vent. \\ This hole drains separated oil that collects in the cavity back into the motor. \\ Be aware that opening the bottom port in the breather can affect the oil drain-back feature. \\ A hose connected to that position can still dribble oil out in small droplets from time to time. \\ If the motor is pushing oil out the breather, you may have a ring seal or other problem. \\ Adding a second breather hose will not fix that. It could be a bad breather valve causing that also. |
| * Engine crankcase pressure is designed to have a slight vacuum with the engine running. \\ That is a little confusing as it is a variable (mean vacuum) pressure measurement based on ring seal and RPM. \\ You'll have the most vacuum at idle. As the RPM rises, you'll have less vacuum. \\ Around 5000-5500 RPM, ring flutter will turn the vacuum into a positive (pushing) charge. | * Engine crankcase pressure is designed to have a slight vacuum with the engine running. \\ That is a little confusing as it is a variable (mean vacuum) pressure measurement based on ring seal and RPM. \\ You'll have the most vacuum at idle. As the RPM rises, you'll have less vacuum. \\ Around 5000-5500 RPM, ring flutter will turn the vacuum into a positive (pushing) charge. | ||
| - | * All you are affectively doing with this mod is enlarging the vent outlet size past the breather valve. \\ Enlarging the vent size can raise vacuum and increase ring seal. \\ Note: if your spark plugs get real black and cruddy looking, you might want to remove the internal breather valve and install and external breather valve. | + | * All you are affectively doing with this mod is enlarging the vent outlet size past the breather valve. \\ Enlarging the vent size can raise vacuum and increase ring seal. (see Theorizing the Affects of the Second Hose below) \\ Note: if your spark plugs get real black and cruddy looking, you might want to remove the internal breather valve and install and external breather valve. |
| * It's never a bad idea to periodically test crankcase vacuum with a slack tube (manometer). That way you know what the mod is doing to the inside pressure. \\ See the link at the top of the page. | * It's never a bad idea to periodically test crankcase vacuum with a slack tube (manometer). That way you know what the mod is doing to the inside pressure. \\ See the link at the top of the page. | ||
| * If installing an external breather valve. \\ If you decide to go this route, remove the internal valve as it will also change crankcase pressure with 2 valves in line. \\ Then, you might want to consider installing something like the external Krankvent or others. \\ [[techtalk:ref:engmech05d|Click here]] to see the Converting Head Breathers to Cam Chest Breather page in the Sportsterpedia. \\ That page is for an Evo conversion to cam chest breathing but the Krankvent and plumbing is shown. | * If installing an external breather valve. \\ If you decide to go this route, remove the internal valve as it will also change crankcase pressure with 2 valves in line. \\ Then, you might want to consider installing something like the external Krankvent or others. \\ [[techtalk:ref:engmech05d|Click here]] to see the Converting Head Breathers to Cam Chest Breather page in the Sportsterpedia. \\ That page is for an Evo conversion to cam chest breathing but the Krankvent and plumbing is shown. | ||
| * Do not install a filter on the end of the vent hose. \\ It's not at all necessary as there is normally no vacuum on the outside of the breather valve (just a slight escape of crankcase gasses). \\ (unless your breather valve isn't working properly) \\ The filter adds resistance to the vent pressure coming out of the engine. This resistance can add to goop in the line / filter later. \\ A stopped up filter can also increase the vacuum inside the engine, which on a street bike, translates to weeping gaskets. \\ [[techtalk:ref:engmech05#filter_on_end_of_the_vent_line|Click here]] to see more on installing a vent line filter. | * Do not install a filter on the end of the vent hose. \\ It's not at all necessary as there is normally no vacuum on the outside of the breather valve (just a slight escape of crankcase gasses). \\ (unless your breather valve isn't working properly) \\ The filter adds resistance to the vent pressure coming out of the engine. This resistance can add to goop in the line / filter later. \\ A stopped up filter can also increase the vacuum inside the engine, which on a street bike, translates to weeping gaskets. \\ [[techtalk:ref:engmech05#filter_on_end_of_the_vent_line|Click here]] to see more on installing a vent line filter. | ||
| + | {{:techtalk:ref:engmech:1979-1985_sportster_breather_valve_path_by_hippysmack.png?direct&500|}} ((drawing by Hippysmack)) \\ | ||
| * **Installing the extra hose**: | * **Installing the extra hose**: | ||
