[ducracer081]

I have an 04 749 that I picked up a few months back as a salvage and rebuilt. I've been using it as a commuter for the last three weeks with no issues. Took it to the track this weekend and within 3 laps it was blowing oil something awful! Got it home cleaned it up, got it good and hot and no oil leaking anywhere. Put it back on the stand left it alone, next morning about an 6" circle of oil was under the bike below the airbox vent hose. Why would it not blow oil riding it as my commuter and puke at the track like this?

 

[Bella749]

First, make sure the oil level is no more than half way full in the sight glass (I run mine in the lower 1/3rd) after it's been sitting upright and level for 5-10 mins. It can be easy to overfill these things when changing/topping-up oil.... if it does get overfilled (even by a little) it will puke into the airbox, especially on the track.

If you are still getting oil pukage, check the crankcase vent on the back of the engine to see if you are getting standing oil in there. I like the corse style setup with the valve in the airbox.

If you continue to get alot of oil in the airbox, do a compression/leakdown test to see if you are getting excessive blowby in the rings, which will create excess pressure in the crankcase.

 

[Shazaam]

All engines have some blow-by past the rings, more as the rings wear. As you ride under certain conditions (at high rpm at the track for example) the entrained oil droplets caught by the oil separator build up above the crankcase ventilation system breather. If the amount of oil is too much for the breather return holes the oil ends up in the airbox drain.

The blow-by has been probably been getting worse over time but the system was handling the oil volume well enough for your commute. A compression and leak-down test will tell you more.

(Bella is much much quicker than me!)

 

[ducracer081]

Cool thanks guys, I'll check into the compression and leak down testing. I know the oil level was good, I keep mine at less than half of the site glass. It blew enough oil in 3 laps that its not visible in the site glass, which is what has me concerned and the motor has just past 4k miles on it.