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How does oil end up near the air filter?

  • 15-02-2014 2:29pm
    #1
    rat_race
    Registered Users, Registered Users 2 Posts: 990 ✭✭✭


    On most bikes there's a little clear tube at the bottom of the airbox that collects oil that somehow ends up around there. It should periodically be emptied -- usually no big deal though.

    How the hell does oil get from the engine all the way up to somewhere like the air filter? I've read a few times, that it's fairly normal and nothing to worry about. But how/why? I could maybe understand if the bike is off and falls on its side or something...but while the engine is on, I cannot see how it would be possible, no?

    Or am I mistaken, and this oil came from the oil-soaked air filter itself (which seems the likely explanation to me)?


Comments

  • #2
    rolliepoley
    Closed Accounts Posts: 2,874 ✭✭✭rolliepoley


    It comes from the the crankcase breather.


  • #3
    rat_race
    Registered Users, Registered Users 2 Posts: 990 ✭✭✭rat_race


    rolliepoley wrote: »
    It comes from the the crankcase breather.

    Ah, okay, thanks...that little pipe that vents air (and maybe oil) from the crankcase? That air/oil escaped past the pistons into the crankcase in the first place, right? And it shouldn't happen to a large degree...


  • #4
    rolliepoley
    Closed Accounts Posts: 2,874 ✭✭✭rolliepoley


    it should happen its a cleaning process, pull the plug in the tube under the bike to drain the sludge.


  • #5
    bitburger
    Registered Users, Registered Users 2 Posts: 364 ✭✭bitburger


    as said its from the breather, on most 4 strokes theres a pipe going from the rocker cover into the airbox, if you disconnect this pipe and rev the ending you will sometimes see vapourised oils coming out like a smoke(well steam technically), the reason for this is that the vapours are taken back into the engine and burnt off, its an emissions thing.


  • #6
    CJhaughey
    Registered Users, Registered Users 2 Posts: 14,907 ✭✭✭✭CJhaughey


    rat_race wrote: »
    Ah, okay, thanks...that little pipe that vents air (and maybe oil) from the crankcase? That air/oil escaped past the pistons into the crankcase in the first place, right? And it shouldn't happen to a large degree...
    As the pistons rise and fall they create pressure, this has to be allowed to vent or the pressure will push oil out of the engine oil seals.
    As engines warm the oil and materials expand this also creates pressure
    These are the reasons for a breather and if it was just straight to atmosphere, you could get contamination as debris and dirt is sucked back into the engine as it cools.
    Hence why they use the airbox as a clean area to vent into.


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  • #7
    rat_race
    Registered Users, Registered Users 2 Posts: 990 ✭✭✭rat_race


    Great, thanks


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