How-To: Crank Case Breather Mod (with pics)

[spazz8448]

ok so it will stop my bike from chokeing up and poping in the airbox?

 

[firefighter1c57]

5. Why not just run a line with an open drain--is some pressure needed in the re-route system?

Path of least resistance. If you have a small filter breather to filter the air coming back into the crankcase as it cools, and a open end on the drain, the engine is going to suck unfiltered air through the open end as opposed to sucking air through the filter.

 

[CrazyTexan]

engine is going to suck unfiltered air through the open end as opposed to sucking air through the filter.

I never thought of that. I'm running just an open end hose with a breather filter T-d into it along the line. I figured the pressure of the vapors commin out wouldn't allow anythin to flow back in. There cant be THAT much suction.. its a valve cover breather..right?? It's also along route to suck air in. And if u were to cap the line wouldn't that force all the smog and nasty stuff through the filter and clog it? I think im overthinking this to much now. But good point firefighter

 

[firefighter1c57]

really it's the cool down that sucks air in. Think of the radiator in your car. You're driving it, coolant gets hot, expands, fills the overflow tank. You park the car, engine cools off, and it sucks coolant back from the overflow tank into the radiator.

Same thing with the crankcase. Air in it gets hot, expands, pistons moving up and down create pressure on both sides, air is pushed out. Engine cools, air cools and air is sucked back into the engine. This is how water vapor ends up inside a engine case, especially in winter months when the air contains more moisture.

Yes, the fumes would be forced out the breather, and hopefully, the liquid vapors caught in the line. I'm not really a fan of the line with a breather on it set up. I'd prefer a catch can, but that's just me.

 

[Stevenc150]

...engine is going to suck unfiltered air through the open end as opposed to sucking air through the filter.

The crankcase breathers are check valves to the best of my knowledge, only allowing flow in one direction - Outward. I run no catch-can and have only good things to say, just be careful where you place the open end. Of course there's more than one way to skin a cat on Everything.

 

[snrusnak]

Yes IIRC the valves are one way only. So no air could get sucked into the engine. If I didn't have to worry about oil drops in my garage or driveway I'd leave the hose open...

 

[firefighter1c57]

hmmm, then where does air enter the crankcase?

 

[snrusnak]

Blowby? lol I don't know. I just know when I cleaned the valves on top of the valve covers I blew through them in each direction and there is a ball inside that when air goes from the outside to inside it stops airflow. So it's a one way only valve.

I wouldn't think you'd need air in the crankcase, the volume of air is never changing, and the excess pressure is just from blowby basically, isn't it? So you only need to release pressure, not let it in. I'm not really sure...

 

[firefighter1c57]

wasn't trying to come off as a smartass, I was really asking, how does air enter the crankcase.

No, you need air coming in too. There is a reed valve in the engine case of the Buell engine that checks blow by, but the heating/cooling cycle of the engine itself would require air coming in...

Typical PCV air flow

 

[zaxrex]

IIRC, the PCV is a reed/schraeder valve. The Postive suggests that the pressure differential is always from the crankcase (maximum) to the catchcan (minimum). You need the breather to ventilate if you are collecting the oil in the catchcan, but I think you will have no problems just running an open end (unfiltered air should NEVER enter through the PCV).

 

[snrusnak]

But the buell engine is not setup like that picture you showed firefighter. Both valves on the buell valve covers are one way valves. On that picture and most cars I've seen(modern cars) there is one pcv valve and one breather(to let air in I guess). My truck, for example, has a hose on one valve cover that goes directly to the airbox, then the pcv on the opposite valve cover.

My question then is, wouldn't the pressure get released from the crankcase into the airbox and not out the pcv(path of least resistance)?

zaxrex said what I was trying to say much better lol.

 

[firefighter1c57]

Yes, the picture was a generic PCV system from I car I just googled quickly.

the Positive comes from engine vacuum. The throttle body is sucking air out the airbox, IE placing suction on the end of the tubes from the head. I don't doubt that the PCV is a one way valve, I've never had mine out, but they usually are.

What I'm saying is, if the fitting on the head is a PCV and it is one way. You start up the engine, it's a cool 58* in the garage. You ride for 3 hours and park the bike. Engine is a nice 412*. As the engine cools, and the air in the cases cool, it's going to create a negative pressure in the case. If the PCV is one way, and I do believe you guys that it is, where is air going to enter the case?

 

[snrusnak]

the Positive comes from engine vacuum. The throttle body is sucking air out the airbox, IE placing suction on the end of the tubes from the head.

That makes sense, didn't think about that.

I understand what you mean about the cooling. I don't know though about where air enters the crankcase from, or if it does. Maybe it sucks it in by the piston rings. It is a slow process cooling down so maybe that's enough. The crankcase starts to make a vacuum until there is enough pressure to suck air past the rings?

I don't know...I got my degree in civil, not mechanical lol

 

[firefighter1c57]

Mechanical Engineers build weapons, Civil Engineers build targets

 

[firefighter1c57]

Wouldn't take into account "rapid" cooling. For instance you're riding down the road on a spring day and it starts to rain, or splash a large puddle. Rapid cooling is what tends to suck water into four wheel drive axles. Guys offroad, splash through a creek, and the rapid contraction of the axle sucks water in, usually at the axle seals.

 

[spazz8448]

ok so i did this mod just now. i took it out for like a 7 mile ride. in the first mile it was chokeing up and poping like it always did "which is what i was trying to fix" after it warmed up it was running fine. i pull up in the drive way look at the filter and i notice its smokeing....its not hot though is mine the only one that does this? and is there any harm that can come from this mod

 

[zaxrex]

it's going to create a negative pressure in the case.  If the PCV is one way, and I do believe you guys that it is, where is air going to enter the case?

Piston skirts? Leaky valves?

 

[liquid51]

The positive pressure in the crankcase comes from blowby. The combustion process is pretty intense, and no piston rings operate at 100% efficiency, so some will always get by. When you get washed out piston rings, you get a ton of blowby and compression loss. That can cause all kinds of leaking from your rocker cover gaskets, not to mention power loss. I have an old honda with some bad piston rings. The valve cover leaks like a sieve and when you pull the spark plug wires off the plug, there's oil pooled up in the hole on top of the plug (there's 4 small gaskets around each plug between the valve cover and the head).

The mod can't damage anything as long as you're not somehow blocking the positive pressure; it has to get out somehow, and it'll find it's way out where you don't want it to if you don't give it somewhere to go.

 

[spazz8448]

positive pressure coming from where? i thought it was attached to the vacuum lines so its sucking not blowing

 

[zaxrex]

True. Without vacuum pressure to draw out the blowby, I wonder if the PCV system is working at 100% efficiency?