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Discussion Starter · #1 ·
I've got a 2002 Ducati 900 Sport with the fuel injected 2 valve head engine. It only has 15K miles and runs very well except for a low idle condition that developed in the last couple of months. Techron injector cleaner new plugs and new air filter haven't helped. I'm not overly concerned about that right now though.

It's a big oil leak that's bothering me. By the time I noticed the oil drip the bike was down a quart or so. There was so much oil it was tough to find the source. It seemed to be dripping from the top and staining the lower front fins, the base gasket area, the left engine cover and underneath. Eventually I found a pool of oil in the airbox as can be seen in the attached pictures. The pooled oil appears greenish under my light. The airbox is clean only because I just wiped it down.

Should I just change the breather? If so how do you break that big chunk of plastic loose without cracking it or does it even matter considering it will be replaced?

I'm actually breathing a huge sigh of relief considering alternatives such as major engine gasket replacement.
 

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I could be wrong (often am) but excessive oil in the airbox can mean compression blow-by ... in other words bad piston ring(s). High pressure from inside of the combustion chamber(s) blowing past the rings causing the crank case to be excessively pressurized and forcing engine oil out of the crank breather and ultimately into the airbox.

The only other cause I know of is over-filled engine cases ... too much oil in the engine. The excess gets blown out of the crank breather and into the crank vent line ... usually routed into the airbox (some race bikes eliminate that system and just run the crankcase vent hose right out of the back end of the bike, allowing crankcase gasses to vent into the atmosphere).

I suppose it could be a malfunctioning breather valve. Maybe.

I'm sure smarter/more experienced members will come along soon enough with suggestions.
 

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Discussion Starter · #3 ·
I haven't noticed any symptoms of worn rings. There's no oil consumption, no smoke on startup, I have very good throttle response and performance from idle to 9K+ on the tach. I am very careful about warmup and have changed oil 4 times in the 5K miles I've owned the bike. Almost all my riding is on back roads so I rarely idle. Because of that and no worries about high temps I've been thinking of going with a lighter 0W40 synthetic instead of Mobil 15W50. If I recall correctly, a 40 weight oil is an option in the Ducati manual.
 

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Piston oil rings prevent the cylinder oil film from reaching the combustion chamber. Worn oil rings reveal themselves as smoke in the exhaust.

Piston compression rings prevent combustion gases from entering the crankcase (blow-by). Worn compression rings reveal themselves as high crankcase pressure and higher oil vapor/mist volume flow out through the crankcase ventilation system and into the airbox.

If you are sure that the crankcase has not been overfilled with oil, you need to do wet and dry leak-down tests to determine if the compression rings or cylinder walls are excessively worn.
 

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I hate to be the bearer of bad news but it’s probably not the breather. It unscrews easily, check that air passes out but not in. I would check the cylinder studs , try rotating them , to eliminate the chance of a broken stud. Yours is a later model with better studs but you still need to eliminate the possibility. You need to compare compression on the two cylinders. Compare the leak down of pressure between the two. I had a problem similar to this, but on a ‘96. My front cylinder had the o-ring on the oil return get sucked into the return line and plug it, causing the exhaust side of the head to fill with oil. It then started to leak. A ‘96 has external lines, but I think it could still happen to yours. It’s a good idea not to use thicker oil than recommended in these motors because the return lines are kind of marginal in size , though maybe the internal oil passages you have are a better design.
Clean the engine really well, run it a bit , and blow some talcum powder at it to try to find a leak. The oil in the air box points to a ring issue but more diagnosis is needed.
 

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Discussion Starter · #7 ·
Thanks for the ideas. I'll troubleshoot this one step at a time as I have other bikes to ride and am a patient man. I just can't believe rings are worn or stuck because it runs quite well and doesn't burn oil. After thinking about the replies I took the breather off and found it totally clean with the internal valve moving smoothly and no buildup of any kind. Next, I changed from 15W50 oil to 0W40 and ran the motor until just past red on the oil temp gauge. I'll be monitoring the oil looking to see whether it gets dark quickly indicating blowby. At startup the clanging metallic sound was reduced and went away much faster with the thinner oil. As always I get a nice exhaust flow that's perfectly even between the two exhaust pipes and no smoke. After shutdown I examined the airbox and the pool of oil was gone. There was some minimal dripping I traced to the airbox but with any luck that will be the last of it. It was rainy today so we'll see what happens after tomorrow's planned 30 mile ride.
 

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Clean the oil up, Tomf . It takes like one drop on a tire to put you on your ass. Your family needs you.
 

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Discussion Starter · #9 ·
Duc96r - you have given some good advice. There was oil on my tire today.

The first 15 miles of today's test run were moderate and produced no output from the airbox drain hose. I proceeded with some full throttle running for the next 5 miles or so and pulled over to see a liberal amount of oil draining down to the asphalt (note my airbox drain was previously routed oddly where it was draining all over the engine instead of the ground). I resumed moderate running for the next 15 miles or so and produced no more dripping oil. Based on that, I'm convinced ring blowby is pressurizing the crankcase and ultimately blowing oil out the breather and into the airbox. Some compression and leak down testing are in order. Meanwhile, I'll ride moderately and maybe even rig a catch bottle (yes, lame). My last gasp hope is that the light 0W40 oil I've switched to can possibly unstick a ring before winter sets in. If not I'll start pulling things apart for a winter project.
 
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