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mediumdaddy

yz400f puking oil

10 posts in this topic

What would cause my 400 to be puking oil from (I'm 90% sure ) the hose on the bottom right by the footpeg right behind the gear shift lever? is there like a pcv valve in there or something? it uses a lot of oil, and it doesnt look like its leaking from the engine itself, im almost positive its coming out of that tube. It uses enough that i have to add some each ride. Any thoughts?

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The hose is an open crankcase breather. Some oil loss from the breather under hard running (high rpm and/or lots of throttle) is normal, but only to the extent that it makes a bit of a mess behind the hose, maybe on your boot, and several drops on the garage floor or in the pickup bed. Shouldn't be so much that you need to add oil that often. If the engine has weak rings, the combustion gases that leak past them (blow by) can increase the volume of air that escapes the breather, and can carry an excess of oil with it.

Also, the engine doesn't have to lay down a smoke screen in order to burn a significant amount of oil. If you only average 5000 rpm on your rides, all it takes to burn 200cc an hour is just over one microliter (0.00133 cc) in the cylinder with each power stroke. Rings and valve guide seals are the most likely reason for oil consumption like that if you don't have a major leak.

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Well there is definately a few drops in the shed floor after i park it, and in the truck bed, and it'll drip a few drops when i stop during the ride. There is a mess behind the hose and a little on my A-stars to. It has unreal compression, but i guess the rings could be getting weak. Maybe ill snap a pic and put it on here so you can see the mess and tell me if its a little much or not, cuz i think it is.

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The hose is an open crankcase breather. Some oil loss from the breather under hard running (high rpm and/or lots of throttle) is normal, but only to the extent that it makes a bit of a mess behind the hose, maybe on your boot, and several drops on the garage floor or in the pickup bed. Shouldn't be so much that you need to add oil that often. If the engine has weak rings, the combustion gases that leak past them (blow by) can increase the volume of air that escapes the breather, and can carry an excess of oil with it.

Also, the engine doesn't have to lay down a smoke screen in order to burn a significant amount of oil. If you only average 5000 rpm on your rides, all it takes to burn 200cc an hour is just over one microliter (0.00133 cc) in the cylinder with each power stroke. Rings and valve guide seals are the most likely reason for oil consumption like that if you don't have a major leak.

So gray - am i looking at just replacing the rings? It definately blows oil out during hard acceleration. After i fixed the exhaust leak, i took her out and opened her up, and when i got back, i noticed the rear wheel had oil spots all over it, as well as my boots. Never seen that before, but never had it open like that since i've owned it either. Is weak rings something that i need to be worried about, or will it wait for a while? my mechanic buddy says it'll need a top end and clutch next summer, depending on how much i ride it this year. Valves were in spec when i bought it in may. My wife is really sick of me spending money on this thing so gimme some good news!

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ok perfect. so it isnt going to hurt anything to leave it like it is? weak rings won't score the cylinder or anything?

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Probably not, but don't figure on reusing the cylinder without replating or replacing it, anyway. I wouldn't expect one that old to be usable.

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I have seen this happen from over filling with oil also. Follow the proper steps in checking and filling the oil and dont over fill it.

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Thanks for the reply, but i'm definately not overfilling it. And its not intermittent, its every ride, and its worse at higher rpms.

Gray - Is the yz400f cylinder able to be bored or does it have that nickaleal or whatever its called?

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