what to do with my pcv

[79datsun620]

back when i was young and dumb and did'nt think things through.....oh wait i still do that:lol: anyway i took off everthing that had to do with emmission control including the EGRV thats the only place that u can put the pcv valve. right now i've got the hose piped up to the bottom of the breather and i guess thats working ok but oil is pooling up a little in the breather.any of u guys got some ideas.

Edited December 20, 2008 by datzenmike

[datzenmike]

521 and early 620 L16 intakes didn't have the EGR but did have the PCV valve. Only problem is they are smaller runner diameter than the L20B.

 

Best would be to find the PCV/EGR manifold and re-attach it. This time just disconnect the vacuum line from the carb to de-activate the EGR, or remove it from the little manifold and plug the finger size hole.

[ggzilla]

Yes, the EGR valve won't hurt performance if the the vacuum line is plugged. Except they are quite ugly.

 

The other thing you can do is fit an oil catch can like race cars use. This solves the oil pooling problem, but does not "postively" breath the block like Positive Crankcase Ventilation system does.

[datsunaholic]

Best way to deal with it is "unplug" where the EGR manifold went. How is it covered? If it's a plate and not just a bunch of JB weld (I've seen that) you thread the plate for pipe threads, put a pipe "street" elbow in it then with an adapter attach the PCV and route the hose back.

[hughdogz]

Any pics would help too. :rolleyes:

 

I kind of understand what is going on. The PCV system is pretty much the same on all L-series engines. I have an L28ET, and from what I've gathered over the years, and experience from other guys, here is my "brain dump" on the situation. :blink:

 

The reason you need a PCV (positive crankcase ventilation) is that below the combustion chamber is the crank-case "bottom end" (of course). The rings can't seal 100% by themselves, so you get some "blow by" during the combustion process. If the lower end is under vacuum, this helps the rings seal better, due to the greater pressure differential, which in turn limits the amount of nasty "blow-by" gasses and oil crud.

 

How do you do this? From the factory, there are two provisions to create crankcase vacuum on an L-series, one at the block breather, the other at the cam (valve) cover. Nissan used the block breather connected directly to the PCV valve (tapped directly into the intake manifold). So, whenever your not at wide open throttle (WOT) you are pulling vacuum, sucking the nasty gasses back into intake to get burned again passing through the PCV valve.

 

If you're at WOT, then the PCV valve shuts down for two reasons:

 

1) Since there is no vacuum in the intake manifold at WOT, you can't pull a vacuum inside the block.

 

2) The front cover is the "timing chain cover" that connects the oil pan (below the pistons, where the blow-by exists) to up above the head under the cam cover. Since at WOT, you can't pull vacuum from the intake manifold (through the PCV valve), you can pull vacuum using the cam cover port, which connect to the intake before the throttle body (venturi effect). Another option is to run the cam cover "breather" into the exhaust to pull vacuum that way instead of before the TB.

 

From what I understand, a PCV is basically a one-way valve. It has a weight that is below a spring, so that under vacuum the weight "unseats" and allows flow. However, when at WOT (or under boost in a forced-induction application) the spring will help the weight seat to shut off that circuit since you sure don't want to pressurize the crank case!! :eek: (side thought: Since the weight depends on gravity, the PCV valve won't work the same if mounted horizontally (or upside-down) via a fitting as it would mounted vertically)

 

In addition, having a catch-can will help keep things "clean" but can never make up for the need for a positively "ventilated" system. You can install "breathers" (or catch-cans) on both the engine block port and cam cover port, and the engine will run...but it isn't the same as the way it was designed to operate. :mellow:

 

As for your PCV relocation issue, you can tap into the manifold either by fabricating a bung in the EGR blockoff (with a 180 degree fitting so the PCV valve remains vertical), or else tap a 1/4 NPT hole into the bottom of the manifold to relocate the PCV.

 

Whew! ...I hope I'm right. Someone please correct me if I'm wrong (it wouldn't be the first time).

 

Later, -hughdogz:blush:

Edited December 20, 2008 by hughdogz

[scooter]

u got er there...

 

 

 

one issue with pcv's is that they do suck up a minute amount of oil that cokes up on the intake valves and in the combustion chamber. some are worse than others, i've seen some suck soo much oil through the pcv valve that it smokes like a bastard and causes detonation...

 

i'm gonna try runnin it with the valve unhooked and see if theres less pinging..

[ggzilla]

Yes, that is a problem when the engine is worn.

[datzenmike]

The PCV valve will work in any position. Manifold vacuum pulls it open. The valve is there to prevent a back fire flame from traveling into the crank case and exploding the gas fumes. The highest concentration of gas fumes is on start up with the choke on and a flooded motor. This is also the best chance for a backfire too. I've seen this happen back in the mid '60s. The explosion blew the valve cover off and bent the oil pan on an old Pontiac.

 

If It's coking the intake and valves then it needs rebuilding or new valve seals. There is a baffle and screen inside the block that separates oil oil spray droplets, burnt oil and blow-by is different.

[datsun76_620]

Great discussion fellas....but....

 

Where do you mount the PCV on:

 

-Offenhauser Mani (I don't remember there being a port there...)

or

-A Side Draft setup???

[datsunaholic]

The top vent on an L-series is not there to vent pressure, it's an inlet. It'll let pressure out of it when the PCV is stuck or the engine has excessive blowby. I've seen air filters filled with oil from that.

 

The stock SU sidedraft manifold had a PCV port:

 

 

 

It's filthy, but you can see the PCV hose running to the cross-connector on the SU manifold.

 

I've never had an Offenhauser manifold but I thought when I saw one it had the port like an L16 manifold. The Cannon single-sidedraft manifold I have has no provision for one.

[79datsun620]

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and i through away the egr its long gone sorry about the quality its a picture phone

[Llittle_Llama]

so if you run JUST a catch can, and no piping to the intake..... do you lose and HP, or just engine life?

[datzenmike]

The PCV is benign in operation and has no effect on power if working or not. It is beneficial to keep vapors from collecting in the crankcase and condensing when the engine cools. If they do, water and combustion by-products will mix with and dilute the oil. The PCV valve prolongs the life of any engine by keeping the oil and insides cleaner.

 

When I was a kid in the '60s many '50s cars were reaching the end of their lives. Some with as little as 80K miles on them. 120K was exceedingly good and 100K possible. GM installed oil pumps on their 'new' OHV sixes and push rod V8 allowing oil filters to be used... a big step forward. In '62 PCV valves were added and engine life increased and maintainance reduced.

Edited December 21, 2008 by datzenmike

[79datsun620]

i like this idea,don't know why i did'nt think of that :D

 

"As for your PCV relocation issue, you can tap into the manifold either by fabricating a bung in the EGR blockoff (with a 180 degree fitting so the PCV valve remains vertical), or else tap a 1/4 NPT hole into the bottom of the manifold to relocate the PCV."

 

thanks,hughdogz