Pre-war (up to 1942) 1938 60s 346 need info.

[mattwilk1972]

I am currently changing my exhaust and intake manifold gaskets on my 1938 60 special 346 flathead. I've discovered after removing my manifolds that I have no breather rail or tube there, Just the 2 holes where a tube would hook up to the valve covers. I've heard conflicting posts where the 1938 346 and earlier don't have a tube. Then I've read they have a breather tube. Can someone help me out please.

[Brad Ipsen CLC #737]

The system is described in the 38 shop manual but shown in the 37 shop manual.  The 37 and 38 systems are the same.  It is on page 90 Plate 37 of the 37 manual.  The 38 shop manual was a supplement to the 37 manual, so you need both.  Reproductions are often printed together in one binder.  The system is a positive crankcase ventilation system consisting of a high-speed system and low speed system.  A small pipe with orifice to the intake manifold and a larger pipe to the air cleaner. 

[Tom Beaver]

Here are a couple of photographs of the 38 PCV system that Brad mentioned.  The first image shows the low speed PCV system which consists of the looped tubing which connectes to an orifaced fitting at the base of the intake manifold and terminates at a fitting which plugs into a rubber gromit in the front valve cover. The second image shows the high speed PCV system which consists of 1/2 inch steel tubing which, in this case, connects to a PCV check valve plugged into another rubber gromit in the rear valve cover. The tubing and PCV valve are are attached together by a piece of rubber tubing,  The top of the steel pipe attaches to a fittiing on the back of the air filter housing, which is not shown here.

The idea is that at low engine speeds the high intake manifold vacuum will draw crankcase vapors into the intake manifold and at high engine speeds relatively low pressure in the air filter housing will do the same.

Tom Beaver

[mattwilk1972]

thanks for the info! I appreciate it!

[LaSalle5019]

You may want to install cross over block-off gaskets from Olson's