Crankcase Breather hose

[mluk1]

I'm not sure how the Crankcase breather hose works, when I first got my bike I think a lot of the hoses were in the wrong place. I've been reading that the crankcase breather hose was is suppose to connect to the airbox. But there was never any hose from my airbox to the engine. I'm planning to not use the airbox but everywhere I read it says to get a filter for the breather. BUT I DON'T EVEN KNOW WHERE THE BREATHER IS! What I think is my Crankcase breather was connected to the oil tank??

Here is a picture of a 750 engine that I found on the internet, where is the crankcase breather hose suppose to attach? The little stub coming out the back there?

[mluk1]

I don't know what yeah this engine is, but mine is a 1977 F. If that makes a difference?

[TOOLS1]

The crankcase breather hose comes off the valve cover. It is on the back side in the middle. the engine in your picture does not have the valve cover on it. cyclex has some cool breathes for around $15.00.
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[mluk1]

That's what I thought was it, but I was reading that that was a run off? I had mine going down by the swingarm. If it is a run off why would it need a filter on it? What would go into that little piece on the back of the engine if I was running a different oil tank? Do I just plug that whole up?

[mluk1]

That's what I thought was it, but I was reading that that was a run off? I had mine going down by the swingarm. If it is a run off why would it need a filter on it? What would go into that little piece on the back of the engine if I was running a different oil tank? Do I just plug that whole up?

[TOOLS1]

If you plug that hose your engine will blow oil out every where! Even past gaskets, and the rings. Engine crankcases have to breath. The moving parts inside the engine act like an air compressor sucking air in, and out of the crankcase.
You will need a breather to keep it from sucking dirt into the crankcase. It would be just as bad if not worse then not running an air filter on the intake. hope this explains it.
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[mluk1]

Any idea on what I should do about the little thing I thought was the crankcase breather? The thing on the bottom of the engine that was attached to the oil tank?

[mluk1]

Any idea on what I should do about the little thing I thought was the crankcase breather? The thing on the bottom of the engine that was attached to the oil tank?

[TOOLS1]

That might be an oil line. There should be two.
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[Lucky 1]

So much confusion. WOW

The tube coming off of the bottom of the engine in the rear is for oil overflow from the oil tank or oil fumes with oil droplets to return to the engine from the oil tank.

The tube coming out of the back of the cylinder head is a breather tube and should go to atmosphere OR a canister separator that seperates oily fumes from actual oil and drains it back to the crank case.

You can just take it overboard as long as the engine is not spittin out a lot of oil.

Those filters on the end of a breather hose are nonsense. becasue when that filter is full of oily fumes and oil it will just start blowing oil mist all over your bike and the rear wheel.

The engine always has a few pounds of pressure inside from the air that is underneath the pistons that are going up and down. It has to have a way to get out or it will blow out at the weakest point. usually a oil seal on the trans.  If you feel air leaking out around a trans seal, it is because the breather hose is clogged up. Many times the breather hose is sent back to the air filter box and the gases are reingested and reburned by the engine. Just another way to do it.

[Lucky 1]

Yes a tube goes from the rear of the engine to the same size hose on the oil tank.
There is only one. It is to allow oil to drain back to the engine.

[Piute]

 Hey ! mluk1 you might wont to check this out
http://honda-cb750-s.456789.n3.nabble.com/engine-breather-td3158981.html#a3315566

[Peterwh]

Forgive my ignorance but how can the pistons going up and down create crankcase pressure?  As one piston goes down, another goes up, so the crankcase has constant volume.

[TOOLS1]

If a piston has bad rings it will create pressure in the crank case.
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[Piute]

this post started in March
and his last post on the whole 750s forum was in June

[TOOLS1]

Piute wrote

this post started in March
and his last post on the whole 750s forum was in June

Yea nothing like beating a dead horse, is there?
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[shinyribs]

Peterwh wrote

Forgive my ignorance but how can the pistons going up and down create crankcase pressure?  As one piston goes down, another goes up, so the crankcase has constant volume.

You would think wouldnt you.I have sat and pondered this myself.I have no explanation myself.But I know some of it has to do with the air inside the crankcase heating up and expanding.Some of the mud racers around here use enclosed vents on their crankcases to prevent entry of debris.It looks a lot like a fork gaitor.Round black rubber accordian-looking-thingies.They stretch and shrink as needed.Pretty cool trick.They steal them off of quad rearends.I think its more of an expension issue than it is actual airflow.All the other stugg,the recirculating thru the engine,is more of an emission thing.Just my opinion...could be wrong...probably am.

[Lucky 1]

When the piston goes down there is air trapped under it.

Just like when it goes up and builds up pressure in the combustion chamber.
The difference is the combustion chamber is much smaller volume and is very tightly sealed.


One SAE technical paper writer even suggested using that pressure to supercharge the engine. They tried it and the results were negligible.(not worth while)

As far as emissions... The oily fumes from the crankcase can escape then get on the roads and into the water table.
So that is why most modern machines just have a little cannister to separate the fumes from the oil droplets and send the gases back through the air box and reburn them, and the oil part just drains back to the crank case. Cost you nothing as far as power and keeps your engine compartment clean and the oil off of the roads.

And all motorcyclist do not like oily roads. Roads are safer now for motorcycles than they used to be.

[shinyribs]

Several good points,Donald

[Piute]

 
And all motorcyclist do not like oily roads. Roads are safer now for motorcycles than they used to be.

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  Amen ,thank you