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Old 07-16-2012, 07:48 PM   #1
aculate OP
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Air Intake Silencer

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?

aculate screwed with this post 07-17-2012 at 04:35 PM Reason: Cleaned up some sloppy writing.
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Old 07-16-2012, 09:09 PM   #2
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It controls what the intake howl sounds like.
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Old 07-17-2012, 08:33 AM   #3
Bill the Bong
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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.
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Old 07-17-2012, 04:57 PM   #4
aculate OP
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Aha! I think.

Quote:
Originally Posted by Bill the Bong View Post
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.
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.
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Old 07-17-2012, 06:13 PM   #5
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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.
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Old 07-18-2012, 06:42 AM   #6
The Other JC
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Quote:
Originally Posted by aculate View Post
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.
Yes, this is also where the water gets into the engine block when you flood the airbox on those water crossings!!
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Old 09-19-2012, 07:44 PM   #7
David R
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Laugh

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.
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David R screwed with this post 09-20-2012 at 04:57 AM
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Old 09-20-2012, 05:30 AM   #8
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Quote:
Originally Posted by erkmania View Post
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.
Unless your driveway had you park on a steep uphill then your bug marked its spot nightly.
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Old 09-20-2012, 09:40 AM   #9
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^^^^

Doh. Of course, but that had to be a very steep driveway.
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