Topic: exhaust from the engine head cover

[ray]

Hi, my first post on this awesome forum. Sorry my bad English. (I`m Norwegian)
I just bought my first Honda veteran bike. When I first got it, it did not start. But after adjusting the valves and timing I got it running. There are several issues that I need to figure out, but there is one question I need to ask you Honda experts.

There is a rubber hose on top of the head cover. The hose runs back and ends up together with the overflow hoses in front of the rear tire. When revving the engine a lot of exhaust flows out of the hose. Can somebody please tell my the function of this hose and if something is wrong or not ?!

Me and my "new" CB500 -72



 

[Mandic]

It is your crankcase breather. An engine builds pressure and oil vapor in the air in the crankcase.  When you are revving it up, it builds more pressure.  Especially if your engine is a little worn from time.  Worn rings, valve seals, and other parts can push a little extra pressure into the crankcase. 

[ray]

Thanks Mandic. So it is not unusually that oil vapor will be present in an old engine like this ? I`m thinking of doing a compression test (does not run on all cylinders). If some of the cylinders come out with bad readings, could this much vapor and bad cylinder compression readings have a relation ?