Smoke from crank case breather

[mmaddix]

I have searched and read a thread on this issue but I would like to know could smoke from the crank case breather be caused by burning oil. I just did an oil change and I don't know what the PO was using but I put Yamalube 15W-30. Soon after doing the oil change I noticed the smoke. True fully it might of did it before the oil change and maybe I didn't notice it.

[ManagerMike]

Some vapors from the cc breather are normal, which is why there is a breather tube at all; the crankcase fumes need to be vented (or burned) or else you would rupture engine seals. If it is bellowing smoke however, that may be serious as it indicates a possibly overfilled engine or excessive blow-by. Too thin of an oil will make it worse and 15w-30 is a lighter weight oil than recommended unless you are in a really hot climate.
Do a search for member Catatonic Bug, there is a link to a full downloadable service manual in his signature.

[mmaddix]

I kind of thought the oil would be too thin. The guy at the motorcycle shop said it is almost equivalent to the 20w-40 full synthetic I was looking for. I did notice it was a little over filled but I thought it would be alright (I know it was stupid). So it being over filled could cause the smoke?

[ManagerMike]

Too much oil in an engine results in the crankshaft, along with the rest of the lower parts of the rotating mass, to cause the oil to foam which can result in excessive crankcase vapors, but more importantly, reduced bearing lubrication. Air bubbles do not lubricate engine bearings very well.

[mro]

Your in Southern Cal, I'd use 20/50

[motoman]

Too much oil in an engine results in the crankshaft, along with the rest of the lower parts of the rotating mass, to cause the oil to foam which can result in excessive crankcase vapors,//////////unless REAL overfull, likely not happen as these motors have a windage tray. 20-50w your best bet........and not a synthetic either.........

[mmaddix]

Why not full synthetic?

[fredintoon]

I kind of thought the oil would be too thin. The guy at the motorcycle shop said it is almost equivalent to the 20w-40 full synthetic I was looking for. I did notice it was a little over filled but I thought it would be alright (I know it was stupid). So it being over filled could cause the smoke?

Hi 'dix,
Yeah, overfilling can do that but don't sweat the smoke unless you need to top up the oil every time you buy gas. And switch to 20W50. 15W30 is for Canadian winters.
As to what kind of oil, I believe in using any name brand motorcycle rated non-synthetic oil in the engine because some brands of synthetic oil can induce clutch slip.
I do use synthetic gear oil in the middle drive and rear drive.
Note that oil preference is a religious thing and that stating your choice can produce nasty comments from those of a different belief system.

[cywelchjr]

Why not full synthetic?

Because these engines REQUIRE 20w low side minimum, whether synthetic or otherwise, AND it needs to be made for a wet clutch, and I've had a hard time finding 20w50 synthetic that was formulated for wet clutches. They have 10w40, but it will drink that stuff like water, and it won't properly protect all the engine parts . Engines designed for lighter weight oils have smaller oil galleries. One of the reasons you want a MC specific oil, is because the transmission is lubed by the same oil as the engine, which means the oil is subjected to things that normal engine oil is NOT, things that normally only transmission oil is, which is formulated differently. So MC oil is formulated slightly differently than automotive oil, they use slightly different, more expensive modifiers for viscosity enhancement (which is what creates multigrade oil) to stand up to shearing caused by the transmission gears, and in our engines the higher oil temps caused by air/oil cooled engines.

And yes, I know synthetics handle higher temps better, but it's finding an appropriate synthetic that meets the specs for THESE engines.