Excessive Oil blowby

I just purchased a 2000 WR400 recently. I am a newbee to motorcycles but a gear head in general. I have noticed what I would consider an excessive amount of oil coming from the crankcase blowby tube. I know if this where my jeep, I would have to consider rebuilding the top end.

I have tried to search for this problem on this board, but have come up pretty short. Is this something that I should worry about. The compression is real tight, runs great, not burning any oil and starts on the first kick without the choke even after sitting for a week. I have noticed that the original owner did very little maintenance on the bike if any at all. The air filter fell apart when I took it out, the oil filter looked like the original one (covered in metal shavings from top to bottom).

Please let me know if I should tear this thing down or just not worry about it at all. I am sure the bike has at least a couple thousand miles on it.

Help! TIA!

Its quite common for people to overfull the oil causing blowback from the overflow tube. Take it for a spin, shut it off and check the oil level. While sitting the oil drains from the frame back into the motor. Check it after its sat a bit, its low, add more, now overfilled and causing blowback. It takes about 1.5 quarts. Allways check it after the ride and not before.

All the things you are saying are normal, oil out the breather tube is due to no baffle in the cam cover and shavings in the oil filter come from the dogs in the box, HTH,

Hey guys,

Thanks a lot for the feedback. I feel much better now. Has anyone figured out a way to route the hose so as not to gunk up the bike. Dirt and oil make a nice cake mix.


What type of oil are you using? A thicker 20W50 (motorcycle oil) would help reduce excessive amount of oil spitting out crankcase vent, which is caused by a worn engine's increased blow-by. You could also check your cylinder and consider getting a new piston and rings...

I am using the Motul 10-50 Synthetic (5100) oil. I know a little oil can make a big mess, but I see oil dripping off the back of the shifter, neutral switch cover, frame, and coated just under the sprocket down.


Have you warmed the bike up good and then checked the oil? I think its overfilled or your countershaft seal is bad. If you clean up the oil, wrap a rag around the end of the vent tube and tape it on, go for a 10 minute ride and you will be able to identify where the oil is coming from. Also check the dipstick after the ride.

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