98 yz400f oil leak??

7 replies to this topic
  • dustindaulton

Posted July 31, 2011 - 05:45 AM


Hello, I'm new to the thread and relatively new to dirt bikes. I had one in jr. high school but i am now 27 so yeah, its been a while. I just picked up a 98 yz 400f for 1,000 bucks. it runs great and starts easy but after riding it leaks oil out of the tube that comes down from the top of the engine on the left side. I've cruised the forums and found out that it is common to leak a few drops of oil here, but i think mine is leaking excessively. after every ride, be it ten minutes or two hours, i end up with about a 4 to 6 inch puddle of oil on the floor. it does not happen quick, but leaks out little by little after it is parked. is this something i need to worry about?

  • dgcars

Posted July 31, 2011 - 05:48 AM


That is your crankcase breather. First off, I would check oil level.

  • DeeCee

Posted July 31, 2011 - 07:43 PM


Agree with dgcars, before you do anything else check your oil level.

To do this you need to run the engine (assuming it is cold) for about 1.5-2 mins at idle. Remove the dip stick (which is at the top of the frame behind the steering head) and check the oil level (screw out the dipstick and check the level without screwing the dipstick in).

  • dustindaulton

Posted August 01, 2011 - 01:13 PM


Thanks for the replies. sorry it took so long to get back to you. I let it idle for about two minutes and checked the oil. It was about half way between full and empty so I don't think it was over-filled. There is a Yamaha dealer just down the road from my house. Is this something I should be taking it to them for, or is it no big deal?

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  • DeeCee

Posted August 02, 2011 - 02:16 AM


Are you sure the excess oil is leaking from the breather hose ? Maybe you have a leak from somewhere else as well.

  • dustindaulton

Posted August 02, 2011 - 03:27 AM


I've looked the whole engine over and it is clean and dry everywhere. If I run my finger around the tube outlet it comes back with a decent amount of oil on it. Also the puddle is directly underneath the hose. I suppose it is possible that it is coming from somewhere else, but if it is I can't tell where. Any common places for it to leak?

  • dgcars

Posted August 02, 2011 - 03:46 AM


No it's not likely the oil is coming from any where else if the rest of the motor is clean & dry. Most likely there is a little bit of 'blow back' from piston/ring wear. So either live with it if the motor is running good, or investigate further. Your choice.

Edited by dgcars, August 04, 2011 - 02:52 AM.

  • dustindaulton

Posted August 02, 2011 - 01:54 PM


Sounds good. Thanks for the advice.

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