Air Intake Silencer

Discussion in 'GS Boxers' started by aculate, Jul 16, 2012.

  1. aculate

    aculate Herk, herk,...Ptooey

    Joined:
    Mar 31, 2012
    Oddometer:
    797
    Location:
    Directly to the Forehead
    I'm curious about the "air intake silencer" on the left side of my camhead (2010 GSA.) The REPROM gives its name, how to take it off and put it back on, but what is it?

    It's a fairly large bore rubber tube connecting the airbox to the left cylinder head, located under the main intake. At first I thought it was an exhaust gas return (EGR) valve thingy, like on cars, but there's no similar tube on the right side as far as I can tell. What does it do? How does it work? How does it silence the air intake? There's nothing wrong with mine, I'm just curious about it. What's it for?
    #1
  2. tjt94

    tjt94 Been here awhile

    Joined:
    Jun 21, 2008
    Oddometer:
    610
    Location:
    Hell Centro, CA (8 miles to Mexico)
    It controls what the intake howl sounds like.
    #2
  3. Bill the Bong

    Bill the Bong Supern00ba

    Joined:
    Dec 20, 2006
    Oddometer:
    1,168
    Location:
    Kalahari South Africa
    I thought that pipe drained fluids (water, oil) from the airbox into the left cylinder. My previous 1150 had a drain in the airbox that did the same.
    #3
  4. aculate

    aculate Herk, herk,...Ptooey

    Joined:
    Mar 31, 2012
    Oddometer:
    797
    Location:
    Directly to the Forehead
    Thanks Bill. That got me thinking, and I went out to the garage to take another look. The hose has an outside diameter of very roughly 28-29mm. That's much bigger than would be needed for just a liquid channel. So I looked at the REPROM again. In another section, they call it the "breather hose from intake air silencer." So it's a breather.

    It does connect the very bottom of the airbox to the head, so it would convey any fluid in the airbox to the engine's innards, just like you say. But, on further inspection, it's connected to the cylinder head at the location where the timing chain runs. So I'm guessing that it is indeed a breather. Everyone knows that the boxer design has serious pumping issues. From TDC to BDC the crankcase volume varies by 1.2 liters (okay, 1,173 cm3, or whatever.) So the reason the hose is so large is to accommodate the resonating air caused by that large change in crankcase volume with each engine revolution.

    In other threads in GSpot, people have said that when you overfill your oil during an oil change, the extra oil winds up in the airbox. This tube must be the path that it takes to get there.
    #4
  5. erkmania

    erkmania Last of the red hot left pipers

    Joined:
    Mar 19, 2004
    Oddometer:
    1,130
    Location:
    San Diego, CA
    That hose is an engine crankcase breather. It's used to ventilate the crankcase gases/pressure into the airbox. On my camhead, the lower cam also has an impeller that is likely used to sling off oil so the intake doesn't consume oil from the sump.

    Nothing new here. VW used a similar setup on their 'Bug' engines just behind the crank pulley and inside the case. It worked pretty well there. That end of the crank didn't have a crank seal, but they never leaked there.
    #5
  6. The Other JC

    The Other JC Lurking since 2004..

    Joined:
    Apr 4, 2010
    Oddometer:
    228
    Location:
    Melbourne, Australia
    Yes, this is also where the water gets into the engine block when you flood the airbox on those water crossings!! :eek1
    #6
  7. David R

    David R I been called a Nut Job..

    Joined:
    Oct 16, 2009
    Oddometer:
    2,753
    Location:
    In Da Swamps of WNY
    Its a crankcase breather hose. Its uphill from the valve cover to the air box. Oil will stick to the sides and run back into the engine. Vapors are then sent to the intake side of the air filter.

    There may be a fresh air vent on the other side or not so the air would flow through the engine.
    My airhead has a check valve to keep the crankcase pressure low. This is one reason they don't leak oil much.

    I had the valve covers off my camhead and all I saw was a trigger for the cam sensor on the right side on the lower cam rear.
    Maybe its an oil blower :)

    Cross a creek? I don't even like riding in the rain.

    Edit: I saw a picture of the end of the cam on another bike. It indeed looks like an oil slinger.
    #7
  8. joenuclear

    joenuclear Planning.....

    Joined:
    Mar 16, 2007
    Oddometer:
    7,274
    Location:
    Fort Smith, Arkansas
    Unless your driveway had you park on a steep uphill then your bug marked its spot nightly.
    #8
  9. erkmania

    erkmania Last of the red hot left pipers

    Joined:
    Mar 19, 2004
    Oddometer:
    1,130
    Location:
    San Diego, CA
    ^^^^

    Doh. Of course, but that had to be a very steep driveway. :deal
    #9