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B-Rock

I dont understand how so much oil get into my airbox!!

24 posts in this topic

I seem to have a chronic problem of always having a ridiculously large amount of oil in my air box. :ride:

When I pull the side panel off to clean/replace the air filter, about a half a cup of oil comes flowing out.

How does so much get in there? And where does it come from?

Has anyone else had this problem? How do I fix it?

I don’t think I have an oil leak anywhere, so how does it get out of my crankcase? :applause:

Am I over filling? When I change the oil, I completely drain it and replace with 1 liter.

I am pretty new too the whole off-road scene and I can’t remember this happening last summer.

Any help would be much appreciated. :thumbsup:

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Is it engine oil? Is your engine oil going down? I would think that loss of a half cup would be pretty noticable from the engine. Are you sure its that much and are you sure your not just overoiling your filter. Do you use proper filter oil or something else. Filter oil is pretty sticky and won't run off.

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On the Canadian versions of the WR, does the crankcase breather tube route into the airbox? I don't like the oil to drip onto the ground so I have mine routed into the airbox and there is always about a 1/4 or so of oil in it after a long ride.

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Is it engine oil? Is your engine oil going down? I would think that loss of a half cup would be pretty noticable from the engine. Are you sure its that much and are you sure your not just overoiling your filter. Do you use proper filter oil or something else. Filter oil is pretty sticky and won't run off.

It's engine oil for sure..........and a ton of it at that. :thumbsup:

Today was the only timed I noticed that my oil level was significantly down. All other times it has seemed normal. During the week I commute on my bike, so I do an oil change every weekend after trail riding (except this time it had been 2 weeks).

:ride:

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Just route the breather hose down to the ground like the YZ450F, YZ250F and WR250F.

Problem solved and clean air into the carby, and doesn't coat the filter in crap.

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On the Canadian versions of the WR, does the crankcase breather tube route into the airbox? I don't like the oil to drip onto the ground so I have mine routed into the airbox and there is always about a 1/4 or so of oil in it after a long ride.

Rich_in_Orlando is right, check the placement of the overflow tube coming off the top of the valvecover. Many reroute this into the airbox, for what reason I dont know (other that trying to waterproof the engine). Why anyone would want oil vapors clogging up their air filter is behond me...... Two things, Two of my buddys and my 99wr400 blow a decent amount of oil too especially on long cummuting rides. The cause, higher rpms for longer periods of time cause the build up of oil vapors to blow over the hump in the stock tube. You can route the tube back down to the left side of the bike and some aim it at the chain for extra lube or simply point it at the ground (stock). I tryed rerouting the tube up to the neck by where you fill the oil and adding a waterproof crankcase breather thinking gravity would solve the problem by itself but it still comes out over long rides. So I routed it back down to the stock location and added a 90 degrees anadized turndown on it and that directs it down to the ground so that it doesent blow all over the back of the bike. Long, short, alot of guys have this same problem, and there are many ways to deal with it. These are a few but one things for certain, if its engine oil in the airbox there has to be a line routed into your airbox for it to be getting there. Get that tube out and reroute it. Its always going to blow some oil, you just dont want it in the airbox!!!!!!!!!!!

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the 05 has the breather routed to the airbox from the factory so rerouting would stop the oil from collecting. But first, do you have the airbox mods done (remove snorkel and cut openings on the side)? if not your sustained high speed running may be creating a bit of a vacuum in the airbox and drawing the oil in. I don't do much sustained high speed and never have oil in my airbox.

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on a trx450 quad i recently worked on it did just that.the breather hose came thru the right side of the airbox and was to close to the air filter causing a suction effect.my wr450 doesn't do what this guys bike is doing though and the breather hose on the wr450 enters on the carb side of the filter.if this is engine oil it might collect from long high rpm sustained runs on the hiway then drain out of the filter.i've noticed that if i over oil my filter 2 things occur.first the bike runs rich due to lack of flow especially at high elevations.the second is that if left to sit excess filter oil collects in thr bottom of the filter.

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Dudes, I think its better to have oil in the air box than dust and crap in the top of the motor. The air in the breather tube goes in both directions, so does any crap that is in the tube. Some crap gets blown out and some gets sucked in. If you've got the breather hanging down outside you "WILL" get grit in the engine. :thumbsup: Next time u take the valve cover off feel around inside there, its usually worse after water crossings and or long downhills with low throttle, especially if the breather tube sits on top of the bash plate where all the dirt and grit sits. :ride:

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walshy, with all do respect bro the air is never drawn into the breather hose..... Ask anyone who understands the phyics of crankcase ventalation, I dont think yamaha would do this stock if that was the case... I have had my valvecover off many times and its clean as a whisle and so is my oil. Yamaha routes it in the airbox now because its better for the envirnment to reburn the crankcase vapors but it causes a mess in the airbox. Think about it, why would you want something that attracts dirt in an area where you want the least bit of dirt. When I clean my air filter, I simply wipe out my airbox with no chemicals and its clean, with oil in there its a pain to clean.

Rule number 4 in the motorcyles owners manual..... Oil and water are bad for an airbox period.

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walshy, with all do respect bro the air is never drawn into the breather hose..... Ask anyone who understands the phyics of crankcase ventalation, I dont think yamaha would do this stock if that was the case... I have had my valvecover off many times and its clean as a whisle and so is my oil. Yamaha routes it in the airbox now because its better for the envirnment to reburn the crankcase vapors but it causes a mess in the airbox. Think about it, why would you want something that attracts dirt in an area where you want the least bit of dirt. When I clean my air filter, I simply wipe out my airbox with no chemicals and its clean, with oil in there its a pain to clean.

Rule number 4 in the motorcyles owners manual..... Oil and water are bad for an airbox period.

Exactly. :thumbsup:

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My 99 had it originally routed to airbox, never throwing out oil.

After head was removed for mainteinance, oil started spewing out.

after almost 2 years riding, replaced rings, valve seals, did valve leak test, all OK, assembled.

still oil coming out of the breather.

Obviously some do and some dont.

Since airbox was filling with oil, I cut the hose and installed a "T" pipe between and extra hose down to the linkage.

Still no good, to much pressure still forced some oil into the a.box.

modded the "T" pipe with extra "knee" pipe facing upward and second knee leveling the tube to the airbox, so the blown oil would hit the barrier and flow out the bottom and the upper breather is still usable for clean breathing.

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walshy, with all do respect bro the air is never drawn into the breather hose.....

Have you ever put your finger over a breather on an 03/04 WR450? Mine sucks and blows, both directions while the engine is running. Some people have even sucked up water through this hose.

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Have you ever put your finger over a breather on an 03/04 WR450? Mine sucks and blows, both directions while the engine is running. Some people have even sucked up water through this hose.

It doesent suck enough to draw anything up into the hose, the slight sucking you are feeling is the pulsing from the carnkcase ventalation but its not an actual sucking, for every slight sucking there is a blowing which balances out. Water is never "sucked up" the hose. It can be shot up the hose by submerging the hose with forward momentum but the hose will never "suck" up anything by itself.............. Its a proven fact, once again, ask any mechanic about the physics of crankcase ventalation and they will confirm what im saying.

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walshy, with all do respect bro the air is never drawn into the breather hose..... Ask anyone who understands the phyics of crankcase ventalation, I dont think yamaha would do this stock if that was the case... I have had my valvecover off many times and its clean as a whisle and so is my oil. Yamaha routes it in the airbox now because its better for the envirnment to reburn the crankcase vapors but it causes a mess in the airbox. Think about it, why would you want something that attracts dirt in an area where you want the least bit of dirt. When I clean my air filter, I simply wipe out my airbox with no chemicals and its clean, with oil in there its a pain to clean.

Rule number 4 in the motorcyles owners manual..... Oil and water are bad for an airbox period.

"I understand the physics of crankcase ventilation" Pretty simple really, piston goes down air is pushed out, piston goes up air is sucked in. If you are hard on the throttle all the time you should get enough combustion chamber blow by to eliminate any negative pressure in the crank case, no drama's. However the average punter cruising around with all sorts of throttle positions, bike positions, bike upside down on the side of a dusty hill comes to mind. In some of these situations grit can live up in the vent hose and will be either blown out or sucked in. Admittedly its probably only clumsy pricks like me that get their bike into these situations, but I have seen a guy stall his bike in deep mud and slop, took him a bit to start back up, then within 20 Min's his top end locked up with grit. :ride: I first noticed grit in the valve cover of my WR426 then WR450. Since re routing its just not happening. I dont get oil in my air box but its opened up pretty well so not a lot of vacum in there. Maybe there is a way to just put a filter on the end of the vent hose, or just have its own little air box. To be honest I dont like the idea of having it in the air box either, there would performance issues for those who race these things. Whatever the answer is it will have to be better than what we have at the moment :thumbsup:

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Well, it is a straight hose right up to the head at least on my '00 anyway, and I guess if you drop/submerge/flip the bike something can get in there for sure even though most of the pressure in that hose is out not in. I've read some guy's have put some kind of filter on it to protect from that. I 've never found anything in the head but I do change my oil often.

But back to the point of oil in the airbox, I think this fella might have a bad ring seal wich is unlikely....more likely is the chance that he is running too much oil in the motor. It's easy to check the oil when the bike's been sitting and refill with too much.

When overfilled these bikes blow the excess out of the breather.

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True about the overfilling. Well you know how I feel, my wr400 leaks like this too and I live with it. My oil is clean and I dont ever have any problems with it. Someone is always going to have a horror story about some friend and what happen to him. Me, I have no problems with it. Yamaha placed it on the skid plate stock for years and they obiously know best or they wouldnt be designing race winning technology. Like I said the only reason they moved it to the airbox in the later years is because its better for the envirnment.

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I suspect the crankcase breather hose has been moved and now vented into the air box. If this is the case, prime culprit would be worn rings/cylinder. As compression leaks past the top of the piston, thsi forms a positive crankcase pressure (blows it up with air basically) and this is what pushes oil out. Will usually be worse under heavy loads. Overfilling it can also do it, but on a dry sump, it has to be way over full.

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Yea I just took my 04 wr450f out for a spin after an oil/filter change and after it had time to cool down i noticed on the ground a small pool of oil? I had the engine degressed before the ride to make sure my bike had no oil leaks. 5700 + km's and approx 4 owners before me its actually a good machine. . Only a small amount of oil came out the valve breather hose and that was after i gave it the beans for about 1hr.

And only 1hr of riding the oil was still clear but the gunk out of the hose was black and sticky. it just builds up and makes a small mess.

mine dumps in the skid plate but with regular servicing its not and issue due to the small amount of oil.

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