ASK THE MXPERTS: I Have Gasoline In My 2009 CRF450 Crankcase. Is This A Major Problem? Is There A Fix?


Dear MXA,
    I am a concerned 2009 CRF450 owner. I have read and trusted MXA’s input for over 20 years. Have you had any issues on your test bikes with gas in the engine oil? Is the EFI leaking fuel into the cylinder after it is shut down? I heard of this gas causing engine damage. Can I ride my bike without fear of it blowing up?

    MXA talked to Honda several times on this matter and Honda is aware of the fact that on some bikes gasoline has migrated to the crankcase (not the transmission). MXA has not had this issue on our test bikes, but yours is not the first letter we have received on the subject.

   Honda says that there is no danger, as long as you drain and change your oil at regular intervals. They think the problem is caused on shut down when the fuel injector shoots (or dribbles) excess fuel into the combustion chamber. As the engine is being shut down, a small amount of gasoline makes its way past the rings and down into the crankcase. It is never enough gas to cause any trouble, but over time, the small amounts of gas can add up.

   This wasn’t as much of problem on a carbureted bike as with fuel injection, but Honda doesn’t know why.

   As long as you change the oil at regular intervals, the accumulation of fuel will not be a problem. Additionally, if you ride the bike very hard or very long to get it up to temperature, the gas will evaporate (although not all of it). Many riders also report a thin fluid of oil on the outside of the engine cases?this is common for riders on long trail rides (not so much motocross).

   Honda did tell us that they do not recommend installing any kind of one-way valve in the gas cap vent hose.

   The gas cannot cause trouble to your crank or rod as long as it doesn’t exceed 15 percent of the gas/oil ratio. In summary, if you change the oil often enough to avoid it collecting in quantity, this will be a non-issue. Changing the oil is good advice for all four-stroke owners, whether they have issues with moisture or gas collecting in the bottom end or not.

2009 fixCRF450four-strokehonda