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Oil over full?

12K views 8 replies 5 participants last post by  cord 
#1 ·
For several years I've had a clacking sound come from my transmission. This past weekend it got significantly worse. It was getting really loud and I could feel it in the machine. I figured that the transmission was finally dying. Then I saw a 12" oil spot on some concrete. I looked under the atv and noted that oil was leaking from the back of the engine on the left side. I pulled the dip stick and couldn't get a reading. I tried again and noticed that it was over full. As in, it was actually coming out of the dip stick hole. The oil is super thin and readily drips off the dipstick. It has a faint gasoline odor. I did notice that my fuel consumption was way, way up, but we were doing a lot of winch work so I didn't think too much of it. The atv runs great and isn't rich. The question is; how can so much fuel get into the oil?
 
#2 ·
I wonder if there is a pcv valve on the crank case like on a car thats stuck open, just a thought.
 
#3 ·
The float could have stuck and if the overflow/drain line is plugged gas will run into the airbox or the motor. Another possibility is hauling the machine with the fuel petcock left on. I would change the oil and see what happens.
 
#5 ·
Well, we located the oil leak. The transmission case is cracked. The crack is about 2" long, is horizontal to the ground and passes through the flange for the rear drive shaft. I'm not sure what's in this area, if it's a gear or a bearing.
 
#6 ·
That doesn't explain the oil being overly full. Excessively thinned oil likely caused a bearing to overheat and in turn caused the crack.

I'm changing the oil in my Rancher 400AT tomorrow. The float was stuck open and the airbox filled with gas. My daughter's boyfriend tried to start it like that and I believe this caused the carb to suck gas right into the engine. I had worked on the carb yesterday and after making sure there was no gas being pushed past the float valve reassembled the plastic today. My youngest daughter was riding it today, the clutch slipped when it got warm from the thinned oil. She immediately parked it and reported to me what it did. The oil was VERY thin and smelled of gasoline.
 
#8 ·
I've had a lot of gravity-fuel-fed engines where the fuel would seep past the float needle, go through the carb and fill the crankcase if I didn't shut the fuel off even while just sitting in the shop. And, I was pretty good about shutting the fuel off. But on rare occasions, if I forgot to turn it off and I was lucky, it hydro-locked the piston and I knew about it the second I went to fire it off or I checked the oil level and saw it was high. The one unlucky time was when I trashed a $4000 Honda F4 racing engine (it ruined the bearings, cam and crank) because the oil was so diluted with fuel it didn't get enough lubrication. I haven't forgotten to shut the fuel off since.
 
#9 ·
Well, the cracked case was caused by a gear shedding two of it's teeth. We're guessing that the loose tooth got pinched between the two gears and then forced the shaft over thus cracking the case. The rear cover can't be serviced with the engine in the machine, so it's getting pulled...
 
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