V-12 intake manifold gaskets

[imported_Phil Knapp]

Here's a question from John Murphy in Florida regarding the differences in some V-12 intake manifolds. I don't have an answer, but perhaps someone on this forum can shed some light on the topic.

"Got a puzzler for you and need your input. Was looking at a V-12 intake manifold gasket prior to mounting on an engine and noticed that there was no hole in the gasket where the tube from the air cleaner is mounted. I checked my other cars and discovered that the gasket in two do not have an opening and two are opened. I wonder how many of our cars do not have the gaskets opened. What about yours? Doesn't not having access to recirculating the crankcase fumes defeat the purpose of the air cleaner tube? I am not a mechanic....just puzzled."

How about it, Dee??

By the way, John has several interesting lincolns, including this gorgeous 1940 Continental. (That bronze color isn't bogus. It's the original special-ordered color for that car.)

[imported_Phil Knapp]

More from John Murphy:

"More on the conundrum;

Went back into the parts garage and polled the spare engines (all used). I have a total of 12 engines with attached intake manifolds. Altogether, four engines have the gaskets pierced with a hole providing access to the crankcase fumes and eight are holeless.

With eight well used engines "holeless" I wonder why the vent tube was ever invented?

Hope the "Forum" can provide some answers.

Ol conundrum John"

[peecher]

The early engines relied on a draft tube for crankcase ventilation and did not have the vent hole in the manifold. I believe that vent hole appeared in '39 or '40? The 4 barrel manifold I got from Austin didn't have this vent because he used an early manifold for a "pattern". Had to drill and tap a hole in it for this tube.

I believe that all "modern" intake gaskets will have provision for the vent and also have large diameter holes for the ports to accomodate the later manifolds, sorta one size fits all. I believe the hole at the front center of the gasket is the intended vent to the valve chamber and any hole in the gasket directly below the vent in the manifold is not necessary as the flow path is thru that front hole, along the top of the gasket to the recess in the manifold diectly below the vent hole on the manifold.

[John Murphy]

Peecher: But how many Zephyrites are running their engines both pre and post war war engines that do not have their vent holes open to remove the gasses? What harm will it cause the engines? Take a minute and check your engine. Remove the vent tube and stick a screwdriver down the vent hole and see if it opened or not. What happens to an unvented engine?

[Guest imported_V12Bill]

The front half of the intake gaskit is solid from side to side and the back half is open. Inside that valve chamber there is a lot of oil mist floating around caused by the hydralic lifters collapsing. Supposedly with the gaskit going from side to side, the oil mist won't be as heavy above the gaskit and the tube will not pick up as much oil and cause blue smoek and decrease of oil level. I doubt that this thinking is logical as the entire chamber will fill with oil mist. With or without the hole in the intake gaskit for the pickup tube there will probable no difference in blue smoke or loss of oil.

[peecher]

As Bill explained there is not a direct passage from the manifold vent to the valve chamber. The manifold fits against the center part of the gasket so most of the "venting" comes thru a hole near the front of the gasket, flows along the top of the gasket and then to the recess directly below the vent hole in the manifold. Blowing thru the tube is the best way to check that the passage is clear. Over time sludge could build up above the gasket surface and hinder or stop any flow. This vent scheme also reduced the amount of stinky, blow-by fumes exiting the oil filler cap. If the passage under the manifold is stopped up you can sometimes work a wire down thru the vent hole on the manifold towards the front of the engine to clear a path for venting. The slightly negative pressure created in the ar cleaner induces flow of the fumes and may even contribute to that "blue" hue out the tail pipe.

I have a feeling this venting scheme was dreamed up also to satisfy owner complaints about stinky blowby fumes in the car? Have no idea how many cars out there that have no venting? Venting of any sort should help reduce the amount of sludge build up.