What I thought was leaking from a valve cover gasket turns out to be something else. Thinking from the leak pattern, the intake manifold gasket (rear part) has failed. I can't think of leakage from anywhere else - the rear main and front main seals are bone dry. Is this a common source of leakage from the FE motors - the intake manifold gasket? Mine is technically not the 1974 390 but a 1967 version, so intake may be a little different.

Second question - is the intake / valley gasket pretty easy procedure for these engines? I have experience w/Ford SB and Chevy SB/BB but not these motors.

Thanks-

 

Intake manifold gasket leak at the rear is the most common leak for a 390. It is a cork gasket and over time it squeezes out. Best way to hold it is remove the manifold and clean the surfaces real good. Use a center punch and put a row of center punch holes along the surface on the block. Use the old style permatex that hardens. This will anchor the gasket. I done it to a 76 F-250 with a 390 ten years ago and it still has not leaked a drop.

 

Yes, as said above very common

Well the FE is a different animal because of the different head configuration.
Care must be taken to align every surface.
I actually prefer to use a silicone bead where the cork usually is. That way the cork (that I don't use) cannot move.
But many do as described above and dimple the top of the china wall to hold the gasket. Just depends on your experience, everybody is different.

 

Dimple the china wall with a punch. You can go the extra mile and also dimple the corresponding surface on the intake.



Position the intake dry to gauge how thick to lay on the RTV. Anywhere from 1/8- to 3/16ths-inch thick is typical.



Clean/degrease both surfaces and lay on the RTV centered on the china wall. Wait about 15 minutes to let the RTV take a set, and then lay the intake square and down. On an FE, install the distributor to align the intake and then torque the intake bolts to spec.

 

Couple questions (apologies):
1. Assume you don't need to remove valve covers for intake clearance?

2. Why 'dimple' the wall? For what purpose?

3. Did Ford or Felpro not make the rear gasket thick enough so that you have to use permatex? I used to use dabs at each corner but never along the block.

4. What do you mean by install distributor first to align intake? Wouldn't you want to install and torque to spec the intake after intake is down?

 

The dimples give the gasket a "anchor" spot. This is the only way to hold the gasket from working it's way out. On your engine you will find the gasket has squirted out. The gaskets are the proper thickness when new but the heat makes them work out. Good old permatex will cement them down providing you make the dimples rough enough to embed into the gasket. Trust me it works, mechanics have been doing this for years. Personally I trust the cork gasket with permatex more than I do silicone. Don't be shy on using the permatex, slather it on good as in this case you are cementing the gasket down not just holding it in place until it is tightened.

 

The VCs need to be removed. If ya observe closely, the outer sides of the intake make up part of the "head" over which the VCs mount.

Dimpling the walls gives the RTV some "feet" to hold onto... moreso than a slick surface. In a sense, they provide friction.

The end seals have a habit of shrinking and swelling with heat and moisture cycles. Eventually they get brittle, crack, or ooze out due to the thermal cycling.

No. Install the distributor before torquing down the intake. Sometimes the intake can be tightened slightly askew and then the dizzy can bind or be misaligned which, in turn, can cause excess wear. Use the dizzy as an alignment tool.

Your call whether you do so.... I am just sharing 30+ years of experience under the hood.

EDIT.... If the RTV oozes out to a point that it is more than just a bulge, that is an indication that ya used too much.

 

So other than the dimpling suggestion and a few others, is the basic procedure in the factory service manual? What RTV is preferred (permatex #1 or 2?)

 

Use permatex #1
It sets up hard and will hold the gasket in place with the dimples. When you dimple the surface, around the dimple will be rough and that is what you want.

 

On pretty well every V8 ever it is common practice to use RTV instead of a gasket on the china walls as a gasket just doesn't do a good job there. The FE is especially susceptible to this.

 

Gee nice to know. Been using the gasket and permatex here in the shop for 50 years now. But then again I never went to college.

 

I'm not saying that what you're doing is wrong. If it works, great. But a lot of people skip the gasket altogether and that works too. It really doesn't matter as long as a seal is made.

 

wile your at it IMO buy an aluminum intake and shave 100lbs of the front of the truck. That intake is a beast to remove by yourself in the truck

 

FE intake is 80lb and aluminum aftermarket is about 15lb.

 

Confirmed on the OEM intake.....the Edelbrock Performer 2105 comes in a 22 pounds.