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REF: Engine Mechanicals - Sub-05I


79-85 Breather Vent Mod Adding a Secondary Vent Hose at 6:00 Position

  • 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. 1)
      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.
  • With the cam cover off, you can see a tiny hole drilled at the bottom of the cavity that by-passes the breather valve.
    • This hole drains separated oil that collects in the cavity back into the motor.
    • Be aware that opening the bottom port in the breather defeats 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.

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