Crankcase pressure to high???

Never noticed on any other bikes ive owned but on the 2010YZ450 the amount of crankcase venting while at idle seems excessive. Likely normal but seems odd (new) to me???

The piston pushes 27 cubic inches of air out from under it every time it goes down, same as it does on top when it goes up. That has to go somewhere. That's why the breather is there. Then of course, the air has to be allowed back in. Because air is compressible, and because there's less time for it to move in and out through the tube at higher speeds, the venting pulses are much smaller at speed than at idle. In an ideal world this would be a net zero sum situation; as much air would exhaust as was drawn in, but the fact is that oil heats up and gives off gasses, and even the best rings leak a little, so there is normally an overall net outflow. When it gets worrisome is when there is an excessive outflow of vapors, indicating weak rings.

Ya, no vapors, I guess im just surprised by the amount of air being moved compared to other bikes. The day I noticed it I compared it to a CRF450 and a KTM 530. Neither of those were anywhere near the pressure/flow as the yami. I will chalk it up to normal for now since the bike still rips hard.

Thanks

Not sure about the KTM, but the CRF has it's breather routed differently, and has a baffle at the engine end of it. The YZF has no baffling at the cam box.

Not sure about the KTM, but the CRF has it's breather routed differently, and has a baffle at the engine end of it. The YZF has no baffling at the cam box.

Perfect, thanks.

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