99wr 400 clean oil in the motor- dirty oil out of the frame?

I put a used 99wr400 motor into a 99yz400 bike and ran it up and down the street once and dumped the oil out of the frame reservoir bolt hole it came out dirty black. The oil out of the motor drain bolt hole come out clean, like new. And the filter area had clear cleanish new oil with the usual debris .

I'm sure something is wrong because I'm of the opinion that after a few minutes running all oil in the motor and frame should have mixed and be about the same in appearance.

I put a hot cam auto cam on this motor and an 06 yz450 carb and it runs great but I'm not sure what to think about the dirty vs clean oil situation?

right now I have a new oil filter in it and new rotella t oil but thought I'd get other thoughts on this situation before running it any more.

Checked the frame screen to ensure it is clean?


Confirmed the pil pump is pumping to the head and to the frame tank?

willaim do you mean crack the oil line fitting going to the head and start it and see if it squirts? same check at tank fitting?

the old motor that was in this bike had the countershaft sprocket side bearing go and chipped up cogs on a gear - so I suspect bitts of crap but if I had a serious blockage wouldn't I hear a serious ticking or hammering sound?

Yes, sort of.


Yes to cracking the fitting at the head. You may have to re-anneal the banjo bolt washers to get them to seal.


On the tank, if you use a bright light and peer into the tank, you should see oil flowing into it.


If you had an engine fail, I'd of thought you'd of flushed the tank alread, cleaned the screw BEFORE putting a 'new' engine in. Then after a few runtime hours, cleaned the scren again, to be safe. If it comes out spotless, leave alone until there is engine work done again. I responded to your PM, giving you a image, Part #2




live and learn I had thought all the tank oil drained out in the tray when the old motor was taken out . Then adding oil and running the new one for a few moments and changing the oil and filter would do it. Next time I would dump solvent in the lines and tank and use compressed air to blow it all out.

Does oil from the tank get filtered before getting pumped through the motor? I better just flush it all now with solvent and air.

Tank----screen---line---oil pump---oil filter----engine----oil sump---oil sump screen----oil pump (stage 2)---oil line---oil tank



OEM manual may have a diagram.



Correct procedure is to remove lines, flush. Flush tank. Run bike, first oli change, inspect tank screen.

The tank flows freely and the bottom line is clear that's all I got so far, the screen had two little flakes in it thats all.

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