Hello,

I've been driving my 56 around with the recently installed 347 crate engine. Not thinking too much about it, I sealed the valve cover vents with push-in K&N filters.

I notice with the engine running there are quite a lot of fumes coming out of these breather filters. I also notice a lot of fumes in the cab when driving in traffic, though that may also be coming from the exhaust which exits just in front of the rear axle.

In any case, I've decided feed the crankcase gases back into the intake. I am not sure if I need breathers with built in PCV valves? Or is it possible to use a regular cap with a holes leading to manifold vacuum? I guess I do not know exactly what the PCV valve does. Is it a simple spring loaded valve that opens at a certain vacuum? How necessary is it?

Any help appreciated.

Gustave

 

The PCV valve controls the amount of air drawn into the intake from the crank case. Without it, at idle, you have the same as an open vacuum leak.

To be a complete PCV system, you need to vent one valve cover into the breather, and vent the other, through a PCV valve, into the intake.

The valve is controlled by a mild spring. At idle, when you have maximum vacuum, the valve is pulled closed by that vacuum. Thus, no vacuum leak. What little "blow by" you have is sucked into the breather. When you open it up you have less vacuum but more "blow by", so the valve is opened by the spring, allowing the intake to evacuate the crank case of combustion gasses and water vapor.

Engines with low vacuum, such as multiple carbs, need a weaker spring.

 

Understood. Thanks for the help.

Gustave

 

Yes, you do need valve covers with a baffle over the opening where either the breather (air inlet) or PCV hose/valve connect. Otherwise you'll suck a lot of oil out of it.

A PCV allows a small amount of fumes to pass at idle, so the PCV valve needs to be matched to your engine size.

 

I had MANY problems with this. It is a commonly misunderstood topic that can lead to gasket failure and severe wear on your engine if not attended to. PCV, or Positive Crankcase Ventalation system, actually sucks the pressure from the engine. Without it, the pressure finds the path of least resistance, often causing rear main leaks, valve cover gasket leaks, intake gasket leaks...basically wherever it can go it will. It often presents itself as a small oil leak, oily valve covers that drip on the headers causing fumes...

The passenger side breather hole should house your PCV valve. You need a valve. The drivers side should be a breather style cap to allow fresh air in. On my setup, I ran the PCV to the carb base in the rear. I have heard of running it to the intake, but I have never done that so I have no clue how it works. I used early Dodge style caps, one with PCV hole, one without. The one without has vent holes on the bottom of the cap to allow air in, while the passengers side is sealed on the bottom. There is a meshy steel wool inside to wick oil. I had part numbers for this stuff, but I lost em. It is all over the counter stuff, and you can use the stock Ford PCV valve. I would put a 90 degree top on it, to prevent kinks while routing to the back of the carb.

Hope that helps.

 

I actually researched this for my flathead. I'm tired of the dump tube puking on my front axle.

I'm going to pop a freeze plug into the dump tube hole, plumbed to run a line from it into an oval breather that will cover both carbs.

For the PCV valve, I'm going to machine a plate to cover the hole where the mechanical fuel pump was, that will have the baffle underneath and the valve on top. I'm going to run it to the vacuum wiper port, just below the rear carb.

Also; I've always wondered why the flathead has a breather oil cap when it has the dump tube open directly into atmosphere? Seems like a waste to me.

 

I have never heard of a vented engine needing a PCV valve before, so this is news to me. I thought the vented oil fill cap, road draft tube, and breather element on the fuel pump stand kinda took care of all of that? I would have even went further to think that eliminating one would not demand an improved system, since it already flowed fairly well.

I don't claim to be an expert of anything...simply asking questions to learn.

 

Actually, I would be eliminating the road draft tube, and creating a closed system. The breather vent would be replacing the road draft tube, and the new oil cap would be sealed. The PCV valve would be added to the rear, where the mechanical fuel pump was.

Added note: the Road Draft Tube is what I call a "Dump Tube." It's just what all the "old timer" mechanics called it where I'm from.

 

Ah...I C. What are the added benafits of this setup vs. the stock design?

 

Performance wise, no benefit at all.

My reason for doing it is to eliminate the small amount of combustion residue that builds up on my oil pan, front axle and tie rod. There is also that slight "exhaust" smell inside the truck at low crawling speeds, and when sitting.

Most people don't notice it, or care. I'm just too picky at times.

 

Added note: the Road Draft Tube is what I call a "Dump Tube." It's just what all the "old timer" mechanics called it where I'm from.

I have always called them the "driveway oiler' tube.

 

Isn't that the truth? That might be why those guys called it a dump tube. It dumps a few drops of oil once in a while.

Yet another reason to get rid of it.

 

Effie, I assume you have an 8BA-type manifold with your dual carbs? It sounds like it.

There is a specific change on 8BA's relative to the 59 series engines with respect to air flow thru the crankcase. Varnish and sludge buildup in the valve chest was always a problem, so they added a tube under the intake manifold, connecting the draft tube hole in the manifold to the crankcase. They have an air inlet (the fill tube) just behind it. With this arrangement, fresh air is swept from the front of the engine in the valve chest, to the back of the valve chest, down into the crancase, forward to the tube and up to the draft tube.

So the best way to add PCV to these engines is to use the same flow path, i.e., put the PCV valve in the draft tube hole. That's all you need to do. Here is my setup.

 

Excellent! You just made my job much easier.
I just need a rubber grommet big enough for the draft tube hole, with a hole small enough for the valve. The cap over the fuel pump hole can be solid.

No need for a baffle under the PCV valve? No problems with combustion gas (blow by) from the oil/breather cap?

Added note: Yes, mine is an 8BA type engine. (8RT) Yours is a good looking engine BTW. But you didn't need me to tell you that.

 

Here's the parts I used:

Help! grommet #42052 Dorman #493-212 for GM engines from '68 - '95

Fram PCV # FV294

I got an AN fitting to adapt to the manifold vacuum connection. The grommet is a little loose in the draft tube hole, so I wrapped it with a copper strip and RTV'd it. Others have used freeze plugs that are drilled for a different grommet.