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Buell Forum » XBoard » Right Breather tube (inside Airbox) puffing out black smoke. « Previous Next »

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Ljivasiv82
Posted on Thursday, October 20, 2016 - 05:33 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

My bike threw up code 21 (AMC stuck open). Opened airbox cover to see if the actuator cycles during start up, nope. From what I read, usually these fail as the plastic teeth strip but this one doesn't even make noise. Anyway, I disabled the exhaust valve in the EMC to get rid of the code and the check engine light.

Since the airbox cover was off I decided to take the airbox off and start the bike. Low & behold there is dark smoke puffing out of the right breather hose. Not super black or a lot of it but definitely noticeable. The left one was completely fine. It was quite warm yesterday and I went on a 40 minute ride through NYC before, lots of heat from stop and go traffic.

The oil should definitely not be overfilled, I put in 2.5 quarts during my 10K service. Dipstick read 2 X's from the bottom. I assume not many people ever ran their bike with airbox off & engine at 180+ degrees, so this might not be something familiar to most.

Is this semi normal or am I looking at a problem? I will try to see if it happens again, as well when the bike is semi warm (150 deg).
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Ljivasiv82
Posted on Thursday, October 20, 2016 - 06:02 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

And if I understand it correct, the right hose is for the rear cylinder, where it gets much much hotter.

Also, there was almost no oil in the airbox compartment. So this is only vapor/smoke, almost no actual oil has come out.
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Griffmeister
Posted on Friday, October 21, 2016 - 11:48 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Since that is relieving crankcase pressure there is really only one source, just two paths. That being the case, I would say you're probably right about heat playing a minor part in making the vapor visible as well as how the airflow makes it's way up to the rocker covers.
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Ljivasiv82
Posted on Saturday, October 22, 2016 - 12:36 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I can't say this wasn't happening before as this was the first time I ever ran the bike with an open airbox.

Would this suggest an issue with the piston rings? Where the pressure is getting through during compression and pushing out the breather hose? Basically the blow-by has become much greater than it normally is when the rings seal properly.

(Message edited by LJIvasiv82 on October 22, 2016)
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Griffmeister
Posted on Saturday, October 22, 2016 - 09:54 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Really, from the sound of it there's no issue here. For one, the seal between piston and cylinder is never perfect or else there would be a lack of lubrication to the upper part of the piston. Second, you have to remember that an engine is just an inefficient air pump. When you say this everyone thinks of the combustion chamber as it changes volume to let air in then pump it out. What they forget is that the bottom of the piston is also changing the volume of the crankcase. A conventional inline four would be volume neutral, two up, two down. A V-twin is different as the stroke is not opposite each other, so with each revolution you are pumping air in and out of the crankcase. Of course this air is moving through oil drain back passages so it will pick up some oil vapor and drag it out the vent. So unless you are dumping out a large amount of oil I would say run with it.
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Brother_in_buells
Posted on Sunday, October 23, 2016 - 04:24 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

The hose from the rear pcv is also the shortest.
And with engine cold or hot makes a different to.
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