The Stovebolt Site Forums The Shop Area Engine Shop Experiencing Excessive Crankcase Pressure?

If anyone has experienced this problem,here are some tricks and tips. http://speedtalk.com/forum/viewtopic.php?f=1&t=23302&sid=e9828e52fc7f87e97132584a41b4d734 I've already installed a P.C.V. valve, and vented oil cap. I have the lines plumbed together,(crankcase and P.C.V.@ oil cap). Since the air/fuel mix creates enough vacuum to cause the pressure,I'm THINKING that the valve cover doesn't need an inlet for air,or am I mistaken?? Should i install a filter at the existing vac. line,at the rear of the valve cover? '55 6500/2-speed,(vac),hydrovac. THANKS!

You must have a vent besides the PCV valve.

Yes,I have the draft tube,and it's plumbed,(stock),to the intake manifold. I installed a "T-fitting,and plumbed the PCV valve into the vented oil cap,from the "T" stem. THANKS!!

You might want to post links to some pictures of your "PCV" system.

You refer to a "draft" tube - a road draft tube is open to the outside/atmosphere and would not be used in a PCV system.

The "stock" PCV system would have had a closed tube in place of the road draft tube?

Here is a recent PCV conversion I did. I also used a vented oil filler cap. Pictures.

Nice looking, Dave

Is there a PCV valve at the converted/closed road draft tube and/or a valve at the left side of the fitting on the intake manifold? Does the right side of the fitting on the intake manifold go to the vacuum wiper?

Yeah, gotta have the vented oil filler cap to prevent negative pressure. I just ditched the road draft tube and did it this way:
http://speedprint.com/deves50/pcvinstall.php
Same theory, different design. If your PCV system is tight, doesnt matter whats in the actual engine road draft hole. I had originally thought putting the valve in the hole would suck oil mist thru the system, but no matter where you put the valve in the line, its the very same unless there is air getting through somehow. No matter how you do it within reason, its a good upgrade.

The valve is in the grommet in the cut off down tube.
Yes, the tube/hose to the rear of the manifold fitting is for the wipers.

Dave, is your PCV valve the type that rattles when you shake it?
If so, doesn't gravity play a part in its intended operation? I see you have your's mounted sideways. BTW, I hesitated before posting this, as you always seem to be way ahead of me in the knowledge department.
On a side note, I was thinking about another way to do the PCV setup on these engines.
Why can't we rig a breather cap in place of the downdraft tube and put the PCV in the valve cover. The main reason we are bothering to do this mod is due to water vapor under the valve cover, not the crankcase. I realize that the water vapor originates in the crankcase, but it naturally migrates quickly to the valve cover. Locating the PCV there (where most, if not all later model manufacturers put them) would provide a rapid evacuation of these damaging fumes. My contention with drawing the fumes from the downdraft tube is that you are drawing the water vapors that have naturally risen to the top of the engine, back down into the crankcase.
Carl

Carl, I've been contemplating moving my PCV from the cutoff draft tube to the valve cover and running a vent line from the cutoff draft tube to the oil bath air cleaner. My current PCV setup is like Dave's so I would be reversing the venting, so to speak.

It's not that the system doesn't work as is, but I can't help but notice the steady flow of bypass gases coming from my vented cap and vent slots on the VC when running. It seems the engine prefers to vent it's crankcase up top as opposed to via the draft tube. At least it does to my layman eye....

Later model ICE's went this route.

Dave

Carl, If you look at the way a PCV valve is designed, with an internal spring holding the valve most of the way closed, (in the engine off position), gravity does not seem to play a part in its function(although you had me rethinking it). I looked at all of my PCV's including early V8 style ones that sat horizontal originally and all seem to be about the same in design.
I have set up a number of 235's this way and all worked well.
The reason I have done this conversion is not for water vapor but because of customer complaint of blow-by smell.

Well that's exactly why I was hesitant to question you originally. Your PCV is different from the older ones which were checked by shaking them. If they rattled, they were good. If they didn't, they were gummed up and needed cleaning.

I like the idea of drawing filtered air from the air cleaner.

Why not use the factory PCV setup? My '53 6400 has it.

Hey Don, do you have a stack of NOS set-ups laying around

point taken

Don, are there pictures somewhere so we can see what a stock setup looks like? I wonder how hard it would be to emulate the original. Dave, is there enough vacuum to support both the PCV system AND the wipers? I assumed there wasn't so I didn't even try it.

Lastly, these engines werent as tight as the newer ones, so wouldnt the blowby that is common in a more broken-in engine of our vintage, get sucked out of the bottom just like everything else, the same as if you put the valve in the valve cover? You have several ways for the air to get both down and up. The rod passages, etc.

The modern engines pull it from the valve cover, but they are pulling gasses from the crankcase too, not just the top end. Since they designed ours with road draft tubes, while it seems backwards, its doing the exact same thing. No?

Deve, The vacuum wipers still work fine.
I questioned you about the PCV valve you use in an earlier post as it is designed for a larger cube engine and may have a tendency to bleed off to much vacuum. The one I find works better is for the smaller cube engines (194-307),FV237.
Here are some pics of a stock set-up. CLICK.

Yes, if you have a vac wiper system, dont use mine. There is no way the wipers would still work. I personally cant imagine ANY reduction whatsover in vac to the wipers being a good thing, but I have been wrong before. So I see the road draft tube solution you and Dave use is closer to the original setup. Interesting.

When I did this 13 years ago, I had no idea there even was a stock solution. I just did the math and installed the one that would work best if the vac wasnt used for anything else. Works great, but I can see why not for those with vac wipers. Thanks for the part numbers!

Stock PCV set-up in 1954.

The stock PCV system appears to utilize filtered air from the air cleaner, which is better than a breather cap.
But it still sucks all of the water vapor that naturally collects under the valve cover (the highest point in the engine), back down into the bottom of the crankcase.
I would think that a portion of that water vapor would re-contaminate the oil.
Carl

It would not be that hard to modify the road draft tube, which they probably just modified in the first place, to make a very stock looking system. The problem as I see it is that there is no reason to use the air cleaner. The vented oil cap is filtered and makes it so there is no need for return air from the breather, yet understand those who want to make a stock system need to go there.

The way a slightly different one works is, air goes into the vented oil cap at the front of the engine on top. Its sucked through the entire engine through the road draft tube opening on the bottom. The gasses are then vented back through the intake manifold completing the 'circuit'. There are many ways to accomplish this, I have alot of respect for Dave (Squared)'s setups. Since I have decided years ago, that vac wipers are unsafe and an accident waiting for a place to happen (use it as a daily driver and you will eventually agree), I did the math and decided the V8 version PCV valve would make this circuit in the most efficient manner. Reason is, you are sucking from below, as opposed to the standard (newer engines) of sucking from above, then you have to take into account the 'tightness' of the engine and how much air can get from top to bottom in the 50's as opposed to the tightness of a later model engine. This whole thing required a lot of thought deciding what would work best. Then, there is no PERFECT answer because the engine wasnt designed that way. A good sucking PCV system 'could suck oil out of the crankcase if the engine was pretty badly worn and compression ends up an issue. That little oil splash guard thats on all of our engines may not be enough. But if you dont use a strong enough sucking valve, you WILL get blowby out of your oil cap because its not strong enough to suck all the blowby out.

So, we have to ask ourselves.. is the valve you are using sucking air inwards from the top to the bottom of the engine. Not hard to test. Start the engine and blow a little smoke over the vented oil filler cap. If nothing noticeable gets sucked in, your PCV valve isnt good enough. Use a match (carefully) if you are like me and not a smoker. This is why I feel that we wont get to the bottom of the best, most balanced PCV system for our Stovebolts. We dont do enough testing and enough collaboration to resolve it once and for all.

Once its resolved, we can then create a VERY stock looking PCV system using the parts needed to really protect our engines in a very meaningful way and respect the stock enthusiasts out there. Heck even a special kit could be created. This isnt about conjecture and what you might THINK is best. Its about exacting air flow and rate of travel through the system. But, vac wipers change the entire equation. Am I really the only one who feels we have no vacuum to spare in the operation of the wipers alone?

But, not just the vac wipers are a variable, so is the condition of the engine which is huge and I have to wonder if that problem alone would cause it to be very hard to be scientific about it. Thru the life of a stovebolt engine, compression goes from what to what? this variable would have alot to do with a good answer. What do you guys think?

I would imagine that the PCV valve is designed in such a way as to extract as much from the crankcase without creating an overly lean air/fuel mixture. A PCV valve designed from the larger 350 might cause a lean condition and a significant reduction in vacuum wiper performance.
I am not sure what is meant by 'tightess' comparison between early and late model engines. They both are very open between the crankcase and the valve cover via the oil drain back holes in the head/heads.
Carl