yz450f oil leak

Hey all, I bought a 2006 yz450f around the beggining of summer. I had a mechanic change the oil when I first got it and we ran into a problem where oil was spraying out of the front case. After letting some oil out it wasn't as bad and it eventually stopped. I changed the oil and oil filter myself today and when I finished I put in 1 quart of oil. After getting the bike started I noticed a stream of oil running out the top of the case and dripping to the ground. What could be the problem?

Quick quiz: How many drain plugs are involved with an '06 YZ450 oil change?

One on the bottom right of case, and one on the left side. Also the oil filter had oil drain out from next to the screw hole.

If you drained both the sump and the oil reservoir, and changed the filter, then the bike takes exactly one liter of oil (1quart without the filter change).


Where does the oil leak come from?  The vent hose?


Here is a picture of it, it seems to be coming out from behind the area under the hose. Where that box is protruding out of the case.


Today I decided to get a better idea of where it was coming from. I went and wiped down the front of the engine and started the bike. Immediately after starting, it started to leak.

Pic #1


It then started to run down the front of the engine

Pic #2


Here's a picture from the other side

Pic #3


Before shutting off the engine I got one last picture, at first I thought I saw drips of oil coming down from somewhere, but then it looked like it was bubbling up.

Pic #4


It appears to be coming either from the oil tank pressure balance hose (either loose or has a hole in it), or from the fitting it clamps to (loose in the case or cracked).   The fitting is replaceable as a service part, and is a push fit into the case.  If you can wiggle it up and out without damaging it, you can likely reinstall it with some sealer and fix it that way.

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