Ask The Doc. Vol. 1

I've received several questions via email. So I guess it's time to start. This is open to any bike question. Any question deemed to be inappropriate will be forwarded to our parent company -AZ HOLE Performance- for proper disposition. Most of the questions I've received have been bike specific and answered by email. One caught my eye because it's on all bikes and little understood. Crankcase Vent System.

Question: My bike was starting to run a little rough so I pulled apart the air filter housing to see how dirty the filter was. (It's pretty dirty so I'll replace it.) Anyway, that's when I noticed the two hoses that run from the heads through the back of the air filter backing plate were cracked.(Correct me if I'm wrong but I think those are called the crank case breather hoses.) What are their purpose and what will it cause if they're cracked?

Answer: Good question. I'm glad you asked. I think we should study that. Oh wait, that's the answer from the Presidential Debate on TV.
If the hoses are worn and cracked they will suck unfiltered air into the engine, not good. But that's all. The crankcase breather system is part of the emission system. On the down (intake) stroke of each piston, the air in the crankcase has to go someplace, can no longer be vented to atmosphere. That's a big no-no. Very simply how it works: air displaced under the piston, through a series of passages, flows through the roller bearing, into the cam housing, up the pushrod tube, into the rocker box, at which point it is a air/oil mixture, passes through a gauze filter to remove oil, through a one way valve, into the head, through the drilled backplate bolts and hoses, back into the engine to be recycled. Now, the system can become clogged. Simple test: remove air cover and hoses. You should feel air coming out of drilled bolts. If system is clogged symptoms would be oil leaks at cases, pushrods, or oil lines and excessive exhaust smoke.

Any other questions? Feel free.