MTFCA Forum

Hello, I've researched PCV discussions but don't seem to find a picture of a modern PCV Valve addition to a T engine. Please post a picture of an in-situ PCV Valve addition to your T engine. Bonus points for parts list. Thank you!

Or you could do this.
https://www.ebay.com/itm/405911762704

NOT AI. My research: The function of PCV values (Positive Crankcase Ventilation) is to vent some un-burned fuel & gases "blow by" that my leak past piston rings. They were adopted in the 1960's to prevent such gases from getting into the atmosphere. While the Model T oil cap provides for the venting it fails at letting such gases into the atmosphere. Specs for some PCV value require 1 to 3 Hg to operate. Th only preferred intake vacuum spec I could find for the Model T was about 17 to 21 Hg. So that should work for most any PCV valve. The question is if the carburetor air intake is enough or if the intake manifold connection is required. Then again why does one want to add a PCV, State requirement or environmentalist?
One additional note: Vacuum rated hose needs to be used.
The oil filler hole is 1-3/8" ID. Specs for PCV valves are not mentioned although some are at 3/4" OD with 3/8" hose

Some ideas.
https://www.mtfca.com/discus/messages/5 ... 1474776572

Frank,
I think you are confusing two things: the PCV and the EGR.
The PCV vents the crankcase not the exhaust manifold. He would have to put a hole in his oil pan.
The Exhaust Gas Re-circulation takes unburnt fumes from the exhaust manifold.

The PVC dumps oil vapors into the filter before the carburetor.
The EGR dumps fumes into the intake manifold.

Maybe there isn't a picture of a PCV valve you want because the Model T doesn't NEED one?

A PCV system that is properly set up will provide several benefits on a T engine. Such a system will reduce the tendency to leak oil and reduce or eliminate oil mist escaping from the oil filler cap. Crankcase ventilation will be substantially improved, which helps remove moisture and fuel condensate from the crankcase. The small amount of oil mist drawn into the intake will provide some lubrication for intake valve stems and the upper cylinder area. A proper system would require eliminating the throttle rod hole in the block and valve cover and providing a filtered oil filler cap. The PCV valve could be attached to the valve cover throttle rod hole and the PCV hose would be connected to the middle portion of the intake manifold, and both the PCV valve and the opening in the filtered filler cap would need to be sized properly for the engine. Adjustments or modifications to the carburetor might be needed. A well-designed system would keep a very slight vacuum on the crankcase under most operating conditions. At or near wide open throttle, intake vacuum is very weak, and crankcase venting would occur at the oil filler cap. Ideally, the oil filler cap would be connected to an air filter on the carburetor. An engine that is worn out is not a good candidate for a PCV system, since excessive blowby would probably overwhelm the system.

You would also have to find a way to seal up the crankcase where the throttle rod passes between the two center cylinders.

varmint wrote: ↑

Thu Jun 19, 2025 8:15 am

Frank,
I think you are confusing two things: the PCV and the EGR.
The PCV vents the crankcase not the exhaust manifold. He would have to put a hole in his oil pan.
The Exhaust Gas Re-circulation takes unburnt fumes from the exhaust manifold.

The PVC dumps oil vapors into the filter before the carburetor.
The EGR dumps fumes into the intake manifold.

Think you may have confused Frank's post with Mark's eBay link. I clearly mention connections to the oil breather cap. Maybe you can highlight where I mentioned the exhaust manifold

"intake manifold connection"
This is used by the EGR, not the PCV.

Even though I tried to give a complete summary of both, and in the process mention "exhaust manifold", that does not in any way imply that everything that I stated was also stated by Frank. Hope that clears any miscommunication by my part.

Ignacio, haven't you read or heard, the state of Texas is dropping the requirements of annual state inspections so a PVC valve or a catalytic converter is no longer necessary .

But.... are you in an EPA NAA?

TXGOAT2 wrote: ↑

Thu Jun 19, 2025 4:53 pm

But.... are you in an EPA NAA?

Pat, Harris County does have stricter emissions standards, but I was just joking with Ignacio.

I am curious about this because it is said to substantially reduce oil leaks and from what I have read isn't especially difficult to install. I have leaks.

I’d have to give some more though to how the carb would respond to what amounts to a vacuum leak. More practically, by the time you seal everything up enough to make a difference you could just fix your leaks.

Andy

Using a carburetor with an idle mixture adjustment might be sufficient to compensate for the additional air. With either the T or A carburetor, the idle speed adjustment would probably allow controlling idle speed if the throttle shaft was tight.

Pretty sure on the link I posted, that is a hot air pickup not venting into the exhaust manifold.