engine breather filter

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    Hi guys,
    i have removed the stock air box from my twin.
    Is there a particular mini air filter that your recommend to go on the engine breather in place of the stock hose?



    Hi Jett,

    there are small K+N filters available for this purpose, but I don’t use them, because the oil mist is spoiling the area where it exhausts.

    (Excuse my lack of english and I may use the words pipe and tube incorrect.
    It is all about lines made of rubber.)

    I have good experience with a very long (horizontal) rubber pipe routed to the very end of the bike (number plate).
    To avoid spilling oil out there, I fitted a T-shaped piece somewhere below the driver seat, while the long tube has a bend downwards at this place.
    At the T-piece I have fitted a (vertical) tube down to and below the swing arm axle, with a plug at the end.
    Oil mist can condense in the horizontal tube, is collected in the vertical tube and can be drained during normal engine oil swap. (same interval)

    Cheers, Michael


    It is something I have never done. Those I know who have done it just use an aftermarket filter. Michaels advice is from experience and should be followed.


    Hahaha !
    Thank you KK !
    It is tested since more than 20 years and it works very well.

    Just to go back to what it is, the engine breather at all.

    With every rev of the crankshaft of our engines it must compensate a volume / displacement difference of 750 cm³.

    Ok, there is the possibility to compress air to a certain amount, but it needs energy to do so. (Compare to compressor energy demand to get a number). An open vented system reduces this energy loss significantly.

    There is a lot of fresh air going into the crankcase that needs to be filtered (while pistons going up), but there is the same amount of hot air and oil mist coming out there (while pistons going down).

    Ok, there will be a certain difference / interference, some kind of “swing”, related to varying engine revs and frequencies.

    Having the filter right above the engine breather “bell”, it is easy to install, but a bit to large filter body or to less space for it.

    It will filter the “inhale” of the engine, avoiding dust and debris to enter the engine. But it doesn’t work very well (oil mist exiting) when the engine “exhales”.

    Water is a different issue !
    It may and will enter and leave the crankcase throught the “ventilation” system.
    Let’s discuss this later on.

    Cheers, Michael

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