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-techtalk:ref:engmech05i [2020/10/08 15:18]
– [79-85 Breather Vent Mod - Adding a Secondary Vent Hose at 6:00 Position] hippysmack
+
+techtalk:ref:engmech05i [2023/12/22 01:36] (current)
– hippysmack
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   * **79-85 cam covers can be modded to accept a secondary breather vent hose**.
     * There is a plugged hole at 6 o'clock below the 10:00 vent line (to A/C) in the cover (when looking at the cover installed).
     * 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 httphttps://www.xlforum.net/forumsforum/showthread.php?p=5786300sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/198279-cam-chest-vent-hose#post4351302)) \\ 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.
     * 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.
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     * Simply remove the plug and replace it with an 1/8" NPT hose fitting and hose.
 
 {{:techtalk:ref:engmech:breather_vent_fitting_by_spamer80.jpg?direct&300|}} ((photo by spamer80 of the XLFORUM httphttps://www.xlforum.net/forumsforum/showthread.phpsportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/194286-%6083-xlx-rebuid-and-questions-thread/page8?t=2070501&page=8)) {{:techtalk:ref:engmech:secondary_breather_vent_pic2_by_83xlx.jpg?direct&300|}} ((photo by 83XLX of the XLFORUM httphttps://www.xlforum.net/forumsforum/showthread.phpsportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/58041-cam-cover-vent-holes?t=307208)) {{techtalk:ref:engmech:secondary_breather_vent_by_83xlx.jpeg?direct&300|}} ((photo by 83XLX of the XLFORUM, annotated by Hippysmack httphttps://www.xlforum.net/forumsforum/showthread.phpsportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/128453-crankcase-breathing-cycle/page3?t=1332902&page=3)) \\
 
 ====== Theorizing the Affects of the Second Hose ======
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 You can see the 10 o-clock fitting and the 6 o-clock fitting both enter the same cavity. \\
 The oil slinger is the big fat washer on the end of the generator in the (R) pic below. \\
 {{:techtalk:ref:engmech:1979_cam_cover_breather_cavity.jpg?direct&300|}}  {{:techtalk:ih:engmech:oil_slinger_by_screwloose.jpg?direct&400|}} ((photo by Screwloose of the XLFORUM httphttps://www.xlforum.net/forumsforum/showthread.phpsportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/184257-oil-pump-porn/page5?t=1979566&highlight=float&page=5)) \\
 
   *  1977-2003 Sportster engines are very similar as far as crankcase pressure is concerned. 1979-1985 models may have more or less vacuum given piston and seal differences etc., but they can be compared.
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     * So we have mechanical limitations to how much vacuum is created and we have situational conditions that change those limitations.
     * Adding the extra hose removes some of the restriction working back toward the breather valve. \\ It allows the breather to work more efficiently. Again, this is assuming the breather valve is in good working order.
  
  
 
 \\
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     * Both upper and lower vent holes access the internal valve equally and function the same way.
   * **Considerations**. 
     * However, plugging the upper 3/8" outlet and using the lower 1/8" outlet may reduce crankcase vacuum. \\ You also may get more oil drips simply because it is at the bottom (gravity). ((IronMick of the XLFORUM httphttps://www.xlforum.net/forumsforum/showthread.phpsportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/163512-cam-cover-breather-plug?t=1757228))
     * With this mod, you are reducing mean vacuum in the crankcase. This WILL affect crankcase pressure. \\ Reducing the outlet size creates less mean vacuum in the crankcase (more positive pressure). \\ This is good for oil scavenging but not as good for ring seal. \\ However, if you are dealing with oil weeping or leaking at gaskets / seals, this may help to lower vacuum that may be creating it. \\ The best advice is to repair / replace the breather valve and / or bad gaskets or seals. \\ Repeated need for replacing these things is a good indication of too much vacuum.
 
 Here is a 1980 XLH with the 10:00 fitting plugged and the 6:00 hole being used to vent the crankcase. \\
 {{:techtalk:ref:engmech:reverse_breather_hose_location_on_80_xlh_by_hscic.jpg?direct&300|}} ((photo by hscic of the XLFORUM httphttps://www.xlforum.net/forumsforum/showthread.phpsportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/192060-my-completely-original-1980-ironhead/page22?t=2053271&page=22)) \\
 
 

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