Tech: Cheap and easy pcv on your 49-53 ford flathead v8

[V8COOPMAN]

.

This is an old thread, but still a good place to remember a few facts. It's quite possible that PCV valves function opposite of how one might think.

I discovered that PCV valves work in the exact opposite fashion than I had previously believed....check the drawing/chart below! Of course, PCV valves function based on MANIFOLD vacuum produced by the engine. And you should remember that 4-cycle engines normally produce the LEAST amount of vacuum during wide-open throttle (WOT), such as during hard acceleration or 'gettin' on it'! Conversely, the HIGHEST vacuum reading will be experienced at idle, or when the vehicle is traveling on a level surface at a steady speed, and at a constant throttle setting. PCV valves usually consist of a small container with a tiny movable shuttle inside, as well as a tiny spring with varying tension values dependent upon the specific vehicle application. In general, the valve is designed such that the internal shuttle is aerodynamically shaped so that it is able to move in consideration of, and in conjunction with the airflow AND the spring's tension. My biggest mis-understanding in operation was that the valve allows the MOST flow through it as the vacuum reading is at it's lowest, as in WOT (wide-open throttle). The opposite occurs as the vacuum signal increases, like during idle.....when the internal shuttle allows the LEAST amount of flow. This really makes sense when you realize that during WOT (when vacuum is lowest, and the GREATEST flow through the valve is allowed to occur), the largest volume of blowby is being sent past the rings into the crankcase when the highest cylinder pressures are being generated. Inversely, the least cylinder pressure is being produced at idle (when the highest vacuum readings occur), meaning less blowby, and the LEAST flow through the PCV valve.

One more important point....MOST PCV valves are designed to be mounted VERTICALLY, with gravity figuring into the functional parameters. DD

[5851a]

The next step for auto makers used an oil fill cap with a hose that led to the air filter housing for any excess fumes. Believe it was called closed crankcase ventilation. Personally I think they work great for keeping engines cleaner. In the later 60's and up when Ford went to the manifold heated air for quicker warm up the air that entered through the oil filler cap was also warmed. Undersides of valve covers were way cleaner in colder climates than in the 50's and 60's. Most of all that comes from emission standards but had an added side benefit. Trouble came when people didn't understand and started ripping things off. Sorry for going OT with this.

[51 MERC-CT]

Did a test a while back just to verify the presence of a vacuum in the crankcase.

[Zeke3]

Great looking manometer 51 Merc.

[Will D]

Ones says a pcv regulates air flow, the other says it is a controlled vacuum leak.....

Ain't that the same difference? To "control" a vaccum leak is the same as "regulating" air flow(vac leak)....???

[34PKUP]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by Will D

Ones says a pcv regulates air flow, the other says it is a controlled vacuum leak.....

Ain't that the same difference? To "control" a vaccum leak is the same as "regulating" air flow(vac leak)....???

The valve does not regulate the flow, its the vacuum created in the intake manifold that controls the position of the valve.

[miniceptor86]

Is it possible in a good engine for the blow by gasses to exceed the vacuum available to keep the crankcase at negative pressure. As in WOT low vacuum and higher blow by? Would this push the gasses back up the inflow tube. Does the inflow need a one way flow provision?

[34PKUP]

Originally Posted by miniceptor86

Is it possible in a good engine for the blow by gasses to exceed the vacuum available to keep the crankcase at negative pressure. As in WOT low vacuum and higher blow by? Would this push the gasses back up the inflow tube. Does the inflow need a one way flow provision?

If it were a "good engine" it would not have any "blow by gasses" to be concerned with.

[V8COOPMAN]

Originally Posted by miniceptor86

Is it possible in a good engine for the blow by gasses to exceed the vacuum available to keep the crankcase at negative pressure. As in WOT low vacuum and higher blow by? Would this push the gasses back up the inflow tube. Does the inflow need a one way flow provision?

I would think that with THAT much blow-by, it's probably time to consider a serious rebuild. I would THINK that it would be wise NOT to install any sort of check-valve on the "inflow" tube, as that would serve as a safety, relief feature, but WTF do I know?

Below is a drawing of the route for air movements in a stock 8BA. DD

[Ken Henry]

I’ve read that it is normal for crankcase gases to backflow through the breather of fresh air inlet at WOT, since there is very little pressure difference across the PCV valve and that passage is relatively narrow (e.g., 3/8 vs 5/8” or so for the inlet).

[markdtn]

I did this pretty much like the OP in case somebody wants new parts with p/ns. The vacuum port just below the carb on my 1950 F1 iron 8BA intake used 7/16 straight banjo threads (not NPT). I bought a GM disc brake 7/16-20 banjo bolt Dorman/Help 13935 or 13947 (and drilled it to a larger ID) and a 7/16 banjo to 3/8 hose barb fitting off Ebay (AKA 12mm banjo x 10mm barb). I am using a Motorcraft EV68 PCV valve and a Dorman/Help 42052 Grommet. Photo is not great but you can see both ends.

[Ronnieroadster]

Something to consider. We all know a piston going up into a cylinder is pushing air compressing it along the way. The end gaps in the piston rings allows some of this compressing to leak thus going into the engine crankcase. What also takes place is on the down stroke of each piston additional air is also being pumped into the crankcase. The visual air seen from the breather tube is caused by this air movement into the oil pan. A PCV when installed correctly can reduce this pressure caused by the end gap leaks and the downward movement of the pistons. If these crankcase pressures can be reduced the crank shaft seals will actually work much better due to the reduced pressure trying to push oil out of the lower end of the engine. There's a lot to be gained with a good PCV system.

Ronnieroadster

[ajmac]

Although the war years are a bit of black hole when it comes to commercial flathead use, huge numbers were manufactured in Canada and England, not to mention the US for lend lease for Britain. I have a 24 stud 1941 flatty that is lined down to 3 1/16” from the Detroit as Britain had standardised on the 3.6L and only wanted that capacity.
In 42/43 a PCV valve was introduced in Canadian production, it is in the parts book illustration from 1944, there was also a standard extra hole in the bell housing so a full flow oil filter could be fitted as standard. I’ve seen wartime reports that the later engines with PCV were highly regarded in the desert trials as the standard road draft tube engines which also only had the slinger rear crank seal were only lasting 1000 miles between major overhauls!
There was essentially no vacuum generated by the road draft tube in armoured vehicle installations as the engine wasn’t at the front of the vehicle in the air flow. In theory the faster you go in a normal install the more airflow around the road draft tube and the higher the vacuum generated. Note I’m talking about 59A and the earlier 81A, I’ve never seen an 8BA.

[scicala]

Disagree on the under $6 part. The PCV valve is probably more than the $6 by itself, unless you're talking about raiding free parts you have laying around.

[51 MERC-CT]

Originally Posted by scicala

Disagree on the under $6 part. The PCV valve is probably more than the $6 by itself, unless you're talking about raiding free parts you have laying around.

Truly funny, consider this thread started in 2016

[Flathead Fever]

Wikipedia history of the PCV valve.

https://en.wikipedia.org/wiki/Crankc...20the%20engine.

When I was a CA smog tech the State tested us to be tested on all the smog devices every two-years to make sure we knew what benefits they provided and how they operated. PCV systems and better oil is how engines can now last 300,000 miles instead of 50,000 miles. They do help the oil from getting contaminated. Blowby gases eventually contaminate the oil which contributes to sludge buildup. I would never remove a PCV system from an engine, but I also would not install one on a vintage engine because I like them period correct. With no oil filter or PCV system I would just change the oil when it starts to look dirty, or every 1000 miles and it should be fine.

Obviously, Ford thought the crankcase needed a road draft tube in 1949 to keep the oil from getting contaminated. That system worked okay but it was dumping that blowby into the atmosphere contributing to smog. I'd rather look at a chromed road-draft tube than a PCV valve on a flathead.