Understanding PCV Setup with an Inline

[cr_bobcat]

So maybe this isn't the right section to pose this question, but it seems as good as any.

I'm really on the fence over this adjustable PCV valve. reference: viewtopic.php?f=1&t=73925

I'm intrigued by the operation and am convinced that my donor engine for my cylinder head had a PCV valve that was plugged, based upon the amount of build up on the backside of the valves. I'm sure that there were probably some valve guide issues as well but the sludge was ridiculous.

My question is: So how does the PCV setup really work with the inline? I get how it works with a V8. And here's about as good a diagram as I've seen

Here it's easier to understand because the clean air in is through a different valve cover. I'm just not grasping how this works when you've only got one valve cover. Aren't you just recycling the air primarily out of the valve cover itself instead of really venting any of those crankcase gases? Wouldn't a better system for an inline have the PCV valve coming from the crankcase as opposed to the the exact same valve cover as where the clean air is drawn in? It just doesn't seem like an efficient gas evacuation scheme, unless there's some subtle design issue that I'm failing to understand.

Anybody got a good explanation of how the theory of operation works here on the inlines? Does this whole thing work on some kind of venturi principle or something? Seems like that would be a rather inefficient draw.

 

[cr_bobcat]

Maybe I just figured it out. I have a couple spare valve covers in the garage and took a look. There is a pseudo partition in the middle that has a cutout to straddle the rocker shaft. Is that the purpose of this plate? Still seems like it would be less efficient than the v8 example, but I don't see a better option given the shaft mounted rocker system.

 

[bubba22349]

Actually a PCV system only needs a few parts to work well as your above diagram shows.

1. A vacuum source located below the carb base (Manafold Vacuum) connected by hose to the correctly rated PCV valve
2. A Clean air source connected by hose to the valve cover breather (Filtered air from the air cleaner)
3. The PCV valve needs to be located on the oposite end of the valve cover from the Breather Cap on an Inline engine.
4. The correct type of valve cover designed for a PCV system (i.e. It has all the required baffling).
5. All the above parts need to be in good working order.

That's it in a nut shell, the reality is it does not really matter if the engine is an inline engine of 4, 6, or 8, cylinders or is a V type engine of 4, 6, 8, 10, 12 etc. in fact a V8 could also use two PCV valves the operating principals are still the same, by helping to keep the crankcase clean. Good luck

 

[cr_bobcat]

Right. My problem was that I was missing the baffle between the front and back half of the valve cover in my assumptions. I'm referring to the vertical baffle in the middle.

What I've read is that the principle is for the crankcase to work in a slight vacuum. This reduces oil leaks and provides a better evacuation of the gases. With the v8 example, it would appear that this vacuum "should" be significantly better since the system draws the air across the engine, whereas with the inline, you're loosing vacuum because of that not being a closed system between the 2 halves of the valve cover.

I'm sure that I probably would not notice a significant difference in performance or anything like that. I'm just exercising my noodle. That being said, I placed the order for the adjustable valve today.

For those still playing along (I'm sure I've bored 90% of the viewers at home by now), here are some interesting nerd links:

http://www.powerperformancenews.com/tech-articles/an-adjustable-pcv-valve-for-the-street/
http://mewagner.com/?page_id=1130
http://mewagner.com/?page_id=1221

 

[wsa111]

Make sure you get the PCV valve for the exact engine you have. A small engine will not need as much airflow as a big V-8.
If your valve cover is not baffled you need to get a baffled grommet for your valve cover otherwise you will suck oil into the intake.
I also mount the PCV valve on a non-baffled valve cover 3" above the cover via a hose just to keep oil from the intake.

 

[bubba22349]

X 2 your absolutely right on those valve cover baffles they are also very important to a good functioning PCV system that should have also been on my above list i.e. the correct type of valve cover. X2 on Bills comment about using the correctly rated (spec) of PCV valve it's very important for the system to operate as it really should. Good luck

 

[cr_bobcat]

Well, I ordered the adjustable one. I know it cost a fortune compared to one off the shelf, but I'm spending a decent chunk of change on my head and valve work. I want this thing running tip-top and expect it to run for another 30 yrs or whenever I have to pick one of the kids to take over.

 

[cr_bobcat]

I also seem to have at lest 2 different styles of valve cover. I'll try to take inventory here soon and document the differences. I'll take pics of the breather connection types as well as the baffles.

 

[drag-200stang]

I have about 10 none have the vertical baffle,let us know what it is off of.

 

[cr_bobcat]

Here are 3 of the 4. The top one is a leaky Chinese dressup one. No clue where I got it from. I've had it for probably 20 yrs. The middle one with all of the oil buildup is from my donor engine which was a 250 out of a '71 Mustang. The bottom one is the one I posted earlier. I have no clue what it came out of. I need to get ahold of my Uncle. He found the head somewhere for me and had it sitting in his garage for years. Notice that the bottom 2 have the vertical baffle. I have one more on the car right now, but because of the Monte Carlo bar, it's not coming off right now.

Now here's a pic of the same 3 flipped over. Notice that they all have a screw in type of receptacle for the breather. Also take note that the leaky Chinese one swapped the position of the PCV valve from the back to the front.

Here is the one on the car right now. This is an OE cover that has been given a jet hot treatment. Notice it's a PUSH ON (not in) style. Once I do the head swap I'll snap a pic of the internal baffling of that bad boy.

 

[chad]

got several ('68, 170, two 250s, '69 & '75). None w/ the verticle baffel. If U get a measurment let me know.
Thanks in advance!
BTW: been following the adj. pvc story & enjoyin it.

 

[bubba22349]

Any of the three will work but those OEM Ford valve covers are going to work the best! IE the ones having that center baffle. Ford made valve covers both ways with the PCV valve installed in the front or in the rear and the breather on the opposite end. My 77 250 in a Maverick had the breather in the rear and the PCV in the front if you think that might work better for you with the Monte Carlo Bar, but it looks like you have good clearance with it now. Good luck

 

[drag-200stang]

West coast built thing ?

 

[bubba22349]

I don't think so though most of the ones I worked on had California Emissions. I think the baffles like those were pretty standard on the 1974 models and up.

 

[chad]

Any of the three will work but those OEM Ford valve covers are going to work the best! IE the ones having that center baffle. Ford made valve covers both ways with the PCV valve installed in the front or in the rear and the breather on the opposite end. My 77 250 in a Maverick had the breather in the rear and the PCV in the front if you think that might work better for you with the Monte Carlo Bar, but it looks like you have good clearance with it now. Good luck

In the back helps in routing the hose less obtrusively & filling the crankcase w/oil?

Folks don't think I need the 'verticle baffel" then? (VC sez: "Powered by Ford" & has a lill clip on outside, not sure what that's for. Two horiz. baffels inside). Thanks~

 

[cr_bobcat]

Well Chad, that's what I'm tryin to work out in my head. My thinking is that the whole PCV system should work much better with that baffle in there. I think the baffle is right but doesn't mean that the system won't work without it....

 

[chad]

"...system won't work without it…"
All oe items - I like. The 'engineers' designed the stuff in for a reason, warm fuzzy nostaligia feeling for me, low tech durability… Often, we restorers, do a bit of historic researche. Luckily we have some grey hairs to report lived experience… the 60s weren't that long ago (4 me, I wuz 10 - 17 then). BUT, I have no real automotive experience/theory so appreciate all yous guys helps. 'Specially when modin for improvements.
I'll stay tuned…

But seems like this 4WD '69 'stang can get by w/o the vertical baffle? just set up the rest of the PCV system correctly! (good, I'm a fairly inexperienced welder/brazer, can sweat pipe & soder wire tho!). Whadda ya say - put it in?

 

[cr_bobcat]

Me? I'd put it in. But I'm goofy that way. I'll try and snap a closer pic and take a measurement or 2 if you'd like.

 

[chad]

sure all ways love da pic!
(actually I enjoyed the link to the reading on this topic U left us).

 

[turbo2256b]

Back in the late 60s used a what ever PCV valve and a manually adjustable heater flow control valve.