These pictures baffle me...

Excellent! Thanks for the pics!!

So with the original baffle, the air travels into (or out of) the rear of the baffle, up and over the two humps in the baffle and finds it's way to the original tube connection about midway in the valve cover. The bumps in the baffle and cast ribs are the labyrinth that is supposed to separate liquid from vapor.

And the general consensus is that the original factory baffle does a pretty good job of doing just that?

Using your pics, I whipped up a (very) crude sketch of how I think the baffle works. How does this look to you?

That looks about right. I also noticed a fair amount of sealant around the baffle edges. I will have to look at one of the complete units I have to see just which areas are supposed to be sealed. Either way, the baffle does a good job of keeping wet oil away from the breather and vapour flowing freely. I will be putting steel wool in the fitting regardless to work as a flame arrest/oil separator.

Steel wool above the cam? Maybe one of these would work,

Might be interesting to compare a 240Z baffle to a 280ZX baffle.  See if Nissan did any tinkering over the years.  I have an 81 ZX engine in the garage.

Also notice that 1972 doesn't show the flame arrestor.  Maybe it's an EFI thing only.  Edit - it's added in 1973.  Maybe they had a few problems in 72...  Oddly, they moved the PCV description to Engine Tuneup.

Sorry for the distraction.  Seems to fit the geek factor though.  No offense.

Edited July 13, 20177 yr by Zed Head

I bought this cover loose off kijiji. No idea which model engine it came off.

Thanks for the thoughts Zed Head. Note the direction of flow in those diagrams... Metered Into the intake manifold by the PCV and then replaced by clean fresh air pulled into the valve cover nipple. That's the "at idle" flow direction. That direction would probably reverse direction under heavy foot high blow-by conditions, but at idle, the nipple on the valve cover is fresh air in.

On the carbureted cars you ought to be able to pull the hose off the valve cover and the nipple on the cover should pull a slight vacuum. Cap it off for a couple seconds and let vacuum build up in the block. Then it will woosh back in when you unplug the hole. You could do the same thing on the EFI cars, but it'll throw off the air metering system.

Also an interesting thought about potential changes in the design of the baffle over the years. If you've got easy access to something newer, it would be interesting to see if you find the design the same.

Site, I think stainless steel would be a better idea than plastic. Stainless sink scrubby?

Or stainless steel wool:

Edited July 14, 20177 yr by Captain Obvious

  On 7/14/2017 at 2:11 AM, Captain Obvious said:

Thanks for the thoughts Zed Head. Note the direction of flow in those diagrams... Metered Into the intake manifold by the PCV and then replaced by clean fresh air pulled into the valve cover nipple. That's the "at idle" flow direction. That direction would probably reverse direction under heavy foot high blow-by conditions, but at idle, the nipple on the valve cover is fresh air in.

The reverse flow is described in the text, but that would have been a really big image (like your steel wool image).  It's also illustrated in later FSM's with arrows.  Funny how Nissan seems to expect a lot of blowby, sooner or later.

I'll take a picture of the inside of the ZX cover and post it, just for fun.  They were fine-tuning things in the ZX cars, like using a slightly smaller throttle body.  Counter-intuitive, why bother kind of things.

I'm not sure they were expecting "a lot of blowby"... I think it's just the nature of the design. The rings are never a perfect seal, so the amount of blowby lost past the rings will probably be proportionate to the pressure of the explosion. In other words, the amount of blowby will be proportional to the load the engine is being asked to support. Couple that with decreased intake manifold vacuum at high load conditions, and the direction changes. You make it sound like they were expecting higher blowby only on worn engines and I don't know if it was your intention, but I don't think that's the case.

Short story?  I think the flow direction will change even on a new healthy engine. At idle, air flows into the valve cover nipple, but at higher blowby conditions, that blowby will flow OUT of the valve cover nipple.

The original purpose of this thread was to entertain the idea of reversing the default flow direction of the whole system so the "reversed" direction of that upper tube would become the "normal" direction instead. This would also mean that the block connection under the distributor would become the fresh air replace except under high blowby conditions.

My question would have to be. Why are you thinking of doing this? The factory system works very well. Has no real issues. What do you hope to gain?  Other than satisfying your curiosity.....  " If it ain'T broke... "

 Now if it was a VW/Audi that has a very poor PCV system, and has a bad " sludging " problem because of it, I could see why.. But the Nissan system is simple and works very well.