blowing out of crank case vent

5 replies to this topic
  • lit549

Posted July 15, 2011 - 04:47 AM


Well,was installing rekluse and noticed while the bike was running that its pushing alot of air out the vent hose that comes from top of engine..No oil,just alot of air..Its 09 yz450f,supposedly has 20 hrs on it.Judging from loooks of bike its safe to assume its true,bike is clean..Any ideas?Bike runs VERY Strong and has alot of compression(from kick) and is very crisp..thanks..

  • William1

Posted July 15, 2011 - 08:31 AM


It is normal, esp. at idle. That big piston pumps both in the cylinder and out. At slow speeds, it is like a pulse. If you are nervous about it sucking in dirt, put a little filter on it or better, a catch can and a vent under the tank or vent it into the airboot like a WR.

  • lit549

Posted July 15, 2011 - 08:38 PM


well,my friends 10 yz250f does it too.We rode for couple of hours tonight(first ive rode it),and when done there was like a mist of oil sprayed on frame by vent hose.And of course dirt stuck too it,my friends 250---no oil splatter..Maybe they justy overfilled the engine with oil??IDK,bike runs strong though..Im still kinda worried about though..

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  • Sknight

Posted July 17, 2011 - 05:15 PM


It could be a little overfull, your rings could have a little more wear causing higher blowby, if it's sat under the right conditions it could have condensation that got blown out carrying a little oil mist with it.

As stated above it's going to suck back and forth as the piston goes up and down, there's just as much air moving below the piston as above it.

  • lit549

Posted July 17, 2011 - 06:34 PM


Well,im heading to a friends house tomorrow and were gonna do a leak down test,see what the results are there.But for 3000$ i think i gotta smokin deal!! Like i say,it runs very strong and is very clean,but i guess well see shortly..Ill post findings tomorrow..Thanks!!

  • byggd

Posted July 18, 2011 - 09:14 AM


It's normal. Even a little oil coming from the hose is normal ... as long as it's not a harley sized puddle.


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