Using reed valves to pull vapor from PCV?

Hi everyone.

I’ve been working with an old Ford V8 for the past six months. Before they used PCV systems, crankcase gases were vented by a device called a road draft tube. There is an air intake on the oil filler cap and a metal tube connected to the crankcase sticks down below the engine. Above 20mph the Venturi effect pulls crankcase vapors, contaminants and water vapor out of the bottom tube, while pulling clean air in through the oil filler cap at the top of the engine.

Obviously the EPA had an issue with these systems and they weren’t all that effective to begin with. Hence the PCV was born. However, it got me thinking about bikes. When you remove the airbox, the crankcase vents out of the breather (usually into a filter or a tube positioned elsewhere) but doesn’t move any air through the engine to remove contaminants. Even with the airbox connected it is simply pulling gases out of the crankcase, only to be replaced by more blowby gases.

While this is venting excess pressure it doesn’t seem like it’s removing all of the contaminants, gases or water vapor. Reading about the old Fords has told me that these cause issues inside the engine if not scavenged- carbon buildup, rust from water vapor, and acids corroding internals. Hence, people nowadays will ditch the road draft tube and install a PCV system to more efficiently pull fresh air into the engine and suck the vapors out.

On our bikes with the crankcase breather simply open to the atmosphere it is the only source for gases to go in or out. No fresh air is being circulated through the crankcase. I was thinking of some ideas to remedy this.

An active system: Perhaps the pcv hose could run up under the tank, through an oil separator, and connect to one of the reed valves. This would pull vapors out of the crankcase breather and send them out through the exhaust. In fact, some cars actually used a system just like this. The other reed valve could be configured as an air intake for the crankcase. One could remove the reed valve itself, block off the passage to the exhaust valve with a screw, JB weld, etc and put a small air filter on the nipple tucked up under the tank.

This would allow filtered air into the engine through the valve cover, which is pulled through the motor, out of the breather, through the oil separator, and finally out the exhaust port via the other reed valve.

A passive system could be set up with an air intake on one or both reed valves as described with a clamp on filter while the breather hose would be run down just below the back of the motor. If positioned correctly it would make use of the Venturi effect and essentially give you a road draft tube setup.

Some issues I foresee that would need to be evaluated with the active system:

1. Oil vapor not caught by the separator could cause carbon buildup on the exhaust valve stem and seat.

2. Fresh air entering the modified reed valve could put dirt particles onto the valve train components, wearing them at a rapid rate if the filter is not effective.

3. Could still encounter popping on deceleration from air introduced into the exhaust (despite it containing some hydrocarbons it might still cause unburnt fuel to ignite in the exhaust on decel, which is annoying). Keeping it a closed system with some degree of scavenging always taking place would minimize the amount of pure air entering the exhaust.

Lastly, is something like this REALLY necessary to begin with? Ha!

Mostly theory, a little mojo, and the opportunity to benefit your motor.

Thoughts?

What motorcycle is it & does it have the stock airbox?
The crankcase is vented into the airbox on many KZs so that the fumes can get burned by the engine.
Many other models also have a Kawasaki CAS that injects fresh air into the exhaust ports to help burn any unburned fuel. see pic.
Subaru came out with a kind of similar SEEC-T system for their vehicles back in the mid 70s.

... Kawasaki Clean Air System

I wrote a big reply, but then realized it was redundant.

Basically, if Kawasaki didn't think it was necessary to get fresh air in, I guess I'm not going to worry about it. After 40 years, the lesson I learned is just change the oil and filter regularly and the inside will look beautiful.

As a side note, as you are probably aware, there are times when the reed valves must not get air, mostly on deceleration. So you fresh air intake will become the default pressure relief, so it must not have a check valve or you risk blowing the oil seals and gaskets.

What about hooking up some propane to the reed valves so you shoot big flames out the exhaust? That would be cool. :laugh:

I was thinking the same thing...Kawasaki knows what they are doing (for the most part). I can't imagine what's to gain by modding the existing system.

I have an 81 KZ750. I have pods (were on the bike when I bought it, along with the Wiseco big bore kit) so I don’t have an airbox.

I feel what you guys are saying, if it was important Kaw would have put it on. Maybe the point I’m missing is that these old V8s had issues not venting properly but for motorcycles it is probably a moot issue. Not enough blow by or condensation etc to make a difference.

Google pan evac. system's for drag cars

This is a subject I've looked into before. Below pic is what I came up with. Simply using a network of tubing from the oil/air separator port to the pod filters. This duplicates what most bike manufacturers accomplish with the blowby tube going into the air box. Negative pressure drawing the fumes into the engine, added to the air/fuel mixture to be burned. Since then I took it a step further. I have a fitting that fits the oil fill cap hole (customized a baffle to block oil sling from the clutch). From there I ran a tube to a filter. So there's now fresh air intake, pulled from the negative pressure at the pods, and clearing the crankcase. Basically a PCV system using air intake instead of manifold vacuum, and no valve.

I have not the air filter either, but I have installed just a 90degree hoose bend on the oil vent. Is these a problem?

Why shall you have negative pressure on the oil vent port?

gordone, every 2/4 stroke engine has a pulsing positive and negative pressure in the engine case that have to be vent.

For reference ---



Good Fortune!

I understand, so I vent without filter, must maybe looking into some solution then...

If you use a tube from the breather port rearward, I think a lot of folks are looking for wind draft while riding to produce negative pressure and help draw fumes out of the crankcase. This won't do anything at idle. Just the fumes will come out under your seat instead of below the carbs.