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ktmracer53

yz450f valve cover breather tube?

7 posts in this topic

i put my bike on the stand and i noticed a good amount of air is comming out that tube, no oil just some air pressure. is that normal? i never noticed it before. its a 06 yz450f:thumbsup:

Thanks!

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Totally normal, when I first got my bike and took it out I remember the pulses from the breather were spitting up dirt on the ground :thumbsup:

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That's why the breather tube is there, to let air in and out to help equalize crank case pressure. A little more will go out than in due to a small amount of blow-by however.

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That's why the breather tube is there, to let air in and out to help equalize crank case pressure. A little more will go out than in due to a small amount of blow-by however.

Why can't one just cut it off at the top? Why does it hafta go into airbox and/or down by shifter?

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Why can't one just cut it off at the top? Why does it hafta go into airbox and/or down by shifter?

Since the tube sucks in and blows out in rapid succession, if you cut it off short then any dirt near the end will get sucked in and dropped on the cams. With it hanging down like it comes stock under normal running conditions dirt will get sucked up the first couple inches and then blown back out, staying a good 10 inches or so from reaching the cams. The problem with this is if the end of the tube is completely submerged in sand or water when the engine is turned off and the engine happens to come to rest on an up stroke, the negative pressure in the crank case is not quickly reversed and it can suck the debris all the way up the tube into the valve cover (which has happened to a few people). For this reason it is a good idea to rerout it into the airbox where the end cannot be completely submerged in anything, unless the whole bike is under water, in which case water will get in the valve cover anyways.

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