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Old October 3rd, 2022, 02:29 PM   #1
trithemonk
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Engine oil gushing into Airbox

I bought a 2012 Ninja 250R for my wife that only had 900mi on it, but it has been no end of trouble. Currently the biggest problem is that when running engine oil comes steadily up the crankcase breather hose the entire time the motorcycle is running and only ceases after the engine stops. The oil level (when the bike is sitting straight) was about half way up the sight glass, but now isn't visible at all yet still is forced out the breather. It doesn't smell gassy so I don't think the rings are bad, but I don't know what could be forcing the oil out continuously like this. I don't think it's been dropped, but it has been sitting for years apparently. Original owner is unknown.
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Old October 3rd, 2022, 07:06 PM   #2
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If you don't see a line in the sight glass it does sound like something could be filling up the crank case. Probably a good idea to drain the oil and see how much fluid you get.
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Old October 5th, 2022, 07:57 AM   #3
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I would expect that gas has made its way into the oil if it's still pumping into the airbox.

They do normally blow some oil into the airbox, especially with extended high RPM running, but it shouldn't be excessive.

What typically happens is the tank has debris in it, and it gets past the screens and into the carbs, where it keeps the float valves from closing. If the petcock isn't functioning properly (should not flow fuel unless there is engine vacuum) it will not stop the flow of gas when the engine isn't running. When both happen at the same time, gas overflows into the crankcase and mixes with the oil.

You may not be able to tell it's a gas/oil mix through the sightglass.
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Old October 6th, 2022, 07:30 AM   #4
trithemonk
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The oil had a slight Gass smell, but was still close to the original viscosity, based on the finger test. When I removed the carbs. The floats and valves seem to function properly (turns the carbs upside down and blew into fuel inlet, air would not flow when carbs were upside down).
If those problems occurred would it result in the large amount of oil being forced up the breather hose?
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Old October 6th, 2022, 08:55 AM   #5
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Not sure what the cause/answer is here.

I would change the oil, using 10W-40, and fill no more than halfway up the sightglass.

Clean the airbox well, and keep an eye on it.

Oil does work its way into the airbox, but not usually in quantity or very quickly with moderate riding.
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Old October 6th, 2022, 09:48 AM   #6
trithemonk
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I will give that a shot. I'm thinking that also it's somehow creating a vacuum through the case breather or somehow pushing extra air into the system forcing it out, I don't know how that would happen. Maybe something to do with the air solenoid?
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Old October 6th, 2022, 11:32 AM   #7
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If I read that correctly, no fuel in the oil. So I would guess stuck or broken piston rings. The 250 used steel bores so if only 900 miles a good possibility.
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Old October 6th, 2022, 12:26 PM   #8
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yes, do compression test to see if you've got extra blowby pressurising crankcase. Stuck rings can often be caused by using dino oil. Do oil-change using full-synthetic JASO MA oil. Higher detergent levels and lack of burning should clean up rings and help them seal better.
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Old October 21st, 2022, 12:45 AM   #9
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And here I was thinking a hole in the piston myself, stuck rings usually, USUALLY ! don't cause that much of blow by to cause an oil dump out the breather pipe.... BUT....
Like Danno said a compression test is definitely needed !
only if we know that the compression is good can we go on to pin point other things.... we can guess till the cows come home like maybe when you hooked up the breather hoses you plugged them in wrong ???? LOL
....
I had a oil problem on a honda 50cc once it blew oil out the sprocket seal so bad that it used all the oil in a 2 mile ride.... the breather hose was pinched off completely ! fixed that, put more oil in it and pushed the seal back in under the sprocket and never had a problem after that ! LOL....
Breathers need to breathe!!!
...
Resist the temptation to leave the pipe off and just dangle as if it blows out oil it will cover the back tire..... My mother was crippled because of that !
oil on a back tire is bad news ! first corner they came too down they went!
all because I put in too much oil, it needed oil so I put in a quart !.... nobody told me it only needed a few ounces ! I was just a Kid ! LOL
I later found out it took about 7/8's of a quart to fill it from completely empty.... some times we learn things just a bit too late in life !
.......
Bob......
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