How to containing Blow by /oil ?

6 replies to this topic
  • yzjack

Posted July 24, 2011 - 04:49 PM


I am at a loss for a corrective action. I have a 2003 YZ450 that I use for road racing ie supermotard. The existing crankcase breather vents to atmosphere via a 1/2" hose. Obviously this is unacceptabe in a track day environment.
I have tried crankcase catch cans, breather filters, all unsuccessful due to the crankcase must vent. I usually wind up with oil all over the chassis after the filter or catch reaches saturation. Does any one know of a fix? or do I need to turn it back into a dirt bike.

  • KJ790

Posted July 24, 2011 - 05:19 PM


Run the breather into the airbox like the WR has. There is a hole in the airboot that is plugged off on the YZ. On the WR there is a fitting in this hole that the crankcase breather goes to. Buy that fitting from the WR (you may need to buy the crankcase breather hose too so that it is the right length and bend) and run it like that.

  • highmarker

Posted July 24, 2011 - 05:19 PM


have to wonder why it's blowing so much oil to fill a catch can? might try running the level lower? you could run it into the clean side of the airbox with a T in the hose that drops to a sealed catch bottle. Most the oil will go to the bottle and the vacuum on the vent hose will vent the case better than if it was just open to atmosphere.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grayracer513

Posted July 24, 2011 - 05:42 PM


You drain the catch can back to the sump on the fly:

Running the oil level lower has no effect on a YZF because they are a dry sump engine. Too much oil will only raise the level in the crankcase after it reaches the point where there is too much oil to fit in the tank. In that situation, the returning excess is forced out of the tank back to the sump through the pressure balance line.


Posted July 24, 2011 - 08:02 PM


Route your breather tube up over the left radiator so any excess oil flows back downhill to the valve cover, then route it back down in front of the radiator (by a couple inches) so that any spray from washing the bike does not get in and then cap it with a Uni filter vent. Works perfect. If you did a lot of stream crossings you might have to "T" into a second vent line, but I don't see any need on a motard bike.

  • yzjack

Posted July 25, 2011 - 03:58 AM


The excessive oil occurs after a session in which the bike has been run wide open for a 20 minute session, at lower RPM'S it does not do it as bad. I drain my catch can after each session, I was thinking along the lines of an Air/oil seperator might work.

Thank you for your advice

  • grayracer513

Posted July 25, 2011 - 07:06 AM


If you look at the setup swatdoc put together, it drains itself, and functions as a separator. Copied the layout from a couple of pro bikes.

Related Content


2016 YZ450 by CaptainKnobby

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies

Yamaha YZ450F 2017 by Chris.GVS

Yamaha YZ450F 2017
  • * * * * *
  • 1 review
  • Last review by Tommyk_55
  • On January 15, 2017


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  30 replies

BIGBORE FOR YZ450F 2006? by Taattie94

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies

Megabomb Fitment by 288yz450

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.