Topic: Chopped 750k Oil Breather Questions

[mikehelvey]

I picked up a 76 CB750K that I just rebuilt the engine on due to top end issues.  When putting it back I got really confused with the oil vent set up.  I read the forums and got more confused.

Here's how I received the project bike:
1. Top vent vented to atmosphere via 90 degree elbow pointing down behind the carbs.
2. Bottom engine vent vented to atmosphere via hose that exits the front of the tire on chain side.
3. Oil tank itself is vented to atmosphere via a nipple on the top through a cheap oil breather under the seat.

I assume the oil breather is to catch fumes that may exit the tank.  The tank does not have an oil separator like the original pre-K model tanks.  It's just a nipple at the highest point.   I thank the top vent ought to have an oil breather at the minimum, if not routed somewhere else.  And the bottom one... not sure it is needed on the K model but don't want to plug it either.

Thoughts?  I'm about to put oil in it and do an oil pressure test.  Fuel lines will be next once I'm satisfied with the oil setup. 

Thanks. Mike.

[newday777]

Welcome to the forum Mike
I have a K6 in my shop that I'll take pictures of the hoses tomorrow to show how they are run from stock.

[newday777]

So is this a chopper(your title chopped) or a stock bike you are working on?

[newday777]

OK Mike
You said that your oil tank has a vent bung on the top of the tank?
The stock 1976 K6 I have in my shop doesn't have a top vent. It was eliminated beginning on the 1976 K model.
There is a bung at the bottom of the tank that goes to the lower outlet on the back of the motor(see arrows)
The cam cover vent goes over the carbs then down the right side frame in front of the oil tank bends rearward and clamps to the passenger peg frame and vents down through a bracket to hold it pointing down below the passenger peg to the atmosphere.

[newday777]

On the K2-K5 the tank has an upper vent on the back of the tank, it runs down below the swingarm near the left side.
The cam vent goes over the top of the carbs and down below the swingarm and vents to the atmosphere.

[newday777]

No do your part of forums and reply back what you have  and if you have it figured out. 😉

[mikehelvey]

So is this a chopper(your title chopped) or a stock bike you are working on?

Titled copped. Purchased as a hardtail with a springer front end.  Valves and guides were a mess with low compression. After breaking the engine down, turns out it cylinders and rings were not that bad.  Rebuilt the carbs, replaced the rings and guides, seated the valves, and am just getting the engine back in the bike. 

[mikehelvey]

Welcome to the forum Mike
I have a K6 in my shop that I'll take pictures of the hoses tomorrow to show how they are run from stock.

Thanks Stu. I probably didn't make it clear that the bike has a homemade oil tank that has the oil lines as expected, and one vent nipple on top to atmosphere.  I think you answered 2/3 of my questions though.   The top vent on the engine, behind the carbs, is also vented to atmosphere and that seems okay.  What about the bottom vent on the engine?  Was that run back to the oil tank bottom (oil separator) drain like the older models? 

Mike

[newday777]

Welcome to the forum Mike
I have a K6 in my shop that I'll take pictures of the hoses tomorrow to show how they are run from stock.

Thanks Stu. I probably didn't make it clear that the bike has a homemade oil tank that has the oil lines as expected, and one vent nipple on top to atmosphere.  I think you answered 2/3 of my questions though.   The top vent on the engine, behind the carbs, is also vented to atmosphere and that seems okay.  What about the bottom vent on the engine?  Was that run back to the oil tank bottom (oil separator) drain like the older models? 

Mike

The tank was why I was asking if it was chopperized.
Yes the lower vent goes in a bung on the bottom of the tank(but the bung is a long vertical tube inside the tank to the top area of the tank so any blow by oil recycles into the tank oil.