yz400 with oil in cylinder head breather hose

4 replies to this topic
  • mmccarth

Posted April 07, 2005 - 02:36 PM


I'm starting to get some oil leaking out through the cylinder head breather hose (the hose from the top of the cylinder head cover down to a drain near the skid plate/shifter lever). If I park it overnight on the stand after riding it, I will have a small puddle (not just a few drops) on the stand in the morning. Anybody else had this problem and fixed it or have suggestions as to why I'm getting excess oil in the blowby and venting out through this hose?

  • walent215

Posted April 07, 2005 - 02:52 PM


i had a 98 and mine leaked a little like that probably not a big deal right now but you might think about a new top end soon

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  • YZ250F_Rider

Posted April 07, 2005 - 03:23 PM


It's caused by compression ring blowby.

  • grayracer513

Posted April 07, 2005 - 04:19 PM


It's caused by compression ring blowby.

Most likely. Knowing the way YZ 400's hold up, I'll bet it's never been apart, and it may be getting pretty tired. Some oil would be normal, but a significant puddle is too much.

  • YZ250F_Rider

Posted April 07, 2005 - 05:50 PM


Even the newer bikes do it. It has to do with ring end gaps, and it's something we just dont have control over on fresh bikes. But on an old delapidated steed such as that, it's definitely time for a new jug and piston.

Go big young man, make it powerful. And take pics. :naughty:

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