How is a PCV Valve rated?

[XPC66]

Ok I've taken a sample of PCV valves from four car engines. They're all six cylinder and different model valves.

a later model Ford 4.0 I6 unit
a a few years earlier Ford I6 4.0
a Buick 3.8 V6 circa 1990s
and a 1971 Holden red motor 202 cubic in I6

You can see how the Holden unit is made to be disassembled and cleaned. Shame they still arent like that.

I'll try to run some tests over the next week

Here

 

[Lazy JW]

I came into this one late but will add my two cents. I have a 1975 copy of Petersen's "Basic Carburetion and Fuel Systems" No. 5. This information is old but still applies to most of our Ford Sixes.

I shall summarize as best I can from the text.

There are four basic versions of PCV.

Type 1: Has a hose going from the crankcase through a valve to the intake. Manifold vacuum sucks vapors from the crankcase and fresh air enters at the oil filler cap. At WOT the crankcase vapors will exit at the breather cap.

Type 2: Similar to the type 1 except it uses a special oil filler cap and a different PCV valve. The filler cap has a small, calibrated hole big enough to let air in but small enough to maintain crankcase vacuum.

Type 3: This variation has been used by shadetree mechanics to "cure" a worn engine from smoking. It is just a tube from the crankcase to the air cleaner. It doesn't work very well at idle. Some foreign cars use this type with a sealed oil filler cap (no breather). It doesn't actually ventilate with fresh air but does allow the crankase pressure to push blowby gases into the intake.

Type 4: AKA CCV (Closed Crankcase Ventilation) is a combination of Type 1 and Type 3. Remember that a Type 1 allows gases to escape? The Type 4 uses a sealed filler cap to prevent this, and a tube goes from the cap (or rocker cover) to the air cleaner. Fresh air enters the air cleaner, through the tube into the valve cover, into the crankcase, and on to the intake via the PCV valve.

When the Type 4 is at zero vacuum there is no suction into the intake but blowby gases will then go into the air cleaner and down the intake. If an engine has a lot of blowby there will always be some gases going into the air cleaner; this will foul a paper element quite soon. The only real cure is to fix the blowby. Most American cars since the mid 1960's use some variation of the Type 4.

My 1941 John Deere Model "A" tractor has what amounts to a factory Type 3 PCV system; most ag engines used something similar as a road draft tube isn't very effective at plowing speeds (or stationary).
Joe

 

[XPC66]

When the Type 4 is at zero vacuum there is no suction into the intake but blowby gases will then go into the air cleaner and down the intake. If an engine has a lot of blowby there will always be some gases going into the air cleaner; this will foul a paper element quite soon. The only real cure is to fix the blowby. Most American cars since the mid 1960's use some variation of the Type 4.


............

I think you may have misinterpretted the article. The breather hose connects post filter. This ensures filtered air enters the engine when on vacuum and oil vapours don't foul the filter on load. The breather hose itself is usually connected to a steel tube on the carby hat that pokes into the carby horn or on a horn spigot for efi throttle bodies.

 

[Lazy JW]

When the Type 4 is at zero vacuum there is no suction into the intake but blowby gases will then go into the air cleaner and down the intake. If an engine has a lot of blowby there will always be some gases going into the air cleaner; this will foul a paper element quite soon. The only real cure is to fix the blowby. Most American cars since the mid 1960's use some variation of the Type 4.


............

I think you may have misinterpretted the article. The breather hose connects post filter. This ensures filtered air enters the engine when on vacuum and oil vapours don't foul the filter on load. The breather hose itself is usually connected to a steel tube on the carby hat that pokes into the carby horn or on a horn spigot for efi throttle bodies.

Not on my 74 or my 81 Fords (both still have the stock air cleaners). They both use a separate little gauze filter thingy that is fastened to the inside of the OUTER wall of the air cleaner box for filtration. Any bad blowby gases (such as my 81 had when I bought it) will foul the gauze filter as well as the regular air filter. In fact, my 81 was so bad the previous owner had removed the air filter and it looked like an oil bath unit
Joe

 

[XPC66]

That's just a silly way to do it. Can you post a pic?

 

[Lazy JW]

That's just a silly way to do it.....

Reckon that's one of Fords "Better Ideas", eh?

 

[XPC66]

Sounds like one of those committee decisions.

 

[XPC66]

Initial rough tests indicate very low flow on high vacuum (~20"Hg), max flow at about 10"hg and then reducing markedly ~6"hg. As expected from the graphs posted earlier, the flow is not linear.

No suprises really and just validates putting small flow capacity PCV valves on engines with long duration cams.

Still putting together a test rig.

 

[willowbilly3]

When I blow from the engine side, there's literally no restriction. When I blow through the hose end, there is restricted flow. That is, the poppet doesn't fit tightly enough to act as a true check valve.

The valve for this engine has such a weak spring, that the poppet moves off the seat simply by setting the valve upside down. The weight of the poppet can overcome the spring. As a matter of fact, the "test" for PCV Valves is to shake them and listen for them to rattle.

Is it possible that the only difference is the size of the orifices and the diameter of the openings the valves fit/screw into?

Remember one with a broken spring will still rattle. If you have (slowly) fluctuating vacuum you might have some carb issues, maybe float level.
One of the main purpose of the pcv valve is also to keep gas fumes out of the crankcase. I saw a 58 chevy once that the kid built a his own system without the valve and it backfired once and blew the valve covers almost off and rounded the pan to hold another quart.

 

[Lazy JW]

That's just a silly way to do it. Can you post a pic?

Here ya go.
http://img.photobucket.com/albums/v177/ ... 002772.jpg

 

[XPC66]

whale oil beef hooked.

 

[rmt]

whale oil beef hooked.

can he say that?

 

[jamyers]

whale oil beef hooked.

can he say that?

I was wondering if anybody was going to decode it.

 

[rmt]

I let it go to the point the thread seemed to be forgotten. But I thought, am I the only one that got this? Or is it so common, old and obvious no one paid any mind? If so then indeed we have begun sliding down the slippery slope. I thought we had rules.

Aussies. :roll:




(XP, got anymore?)

 

[XPC66]

...............



(XP, got anymore?)

No , do you?

 

[rmt]

Nope. I can go on with spoonerisms all day* but they aren't as good in writing as they are in speech, the opposite of "whale oil".


*Letters and syllables. I do it in my head a lot. I fink it's a thorm of dental misfunction.

 

[66200i6]

I wouder if this is why my vacume reading at the manifold increases just off idle.

Good thread, Ric.