Technical SBC Intake Manifold Gaskets

It was recommended that I repost this here, from yesterday.

Hello. I am new to the H.A.M.B., but a long time car guy. I have a '40 Ford Coupe, a '61 Pontiac Catalina, and a '72 Nova. When I rebuilt the bored 283c.i. Chevy in the '40 9 years ago, I used Fel-Pro 1256 intake manifold gaskets with the Trick Flow 23 175 heads based on recommendations from Trick Flow. The car has an Offenhauser 3 x 2 intake manifold. These are composite only gaskets with no metal core and it looks like they are literally internally pulling apart. I have included pictures, including the original installation, so you can see how far they have moved out from under the intake manifold. I will know more when I remove the manifold of course, but has anyone seen anything like this due to manifold/head movement and/or high engine vacuum over time with composite only gaskets? The intake manifold bolts are only torqued to 20 lb.ft. on the aluminum heads (recommended by Trick Flow, the recommendation may be 25 lbft now) as opposed to 30 on iron heads, but they are still tight and haven't loosened up. Although it's been 9 years since these were installed, there is probably less than a couple of thousand miles on the engine. Some say they don't use the coated metal gaskets with aluminum heads due to the dissimilar metals issue. Others say the Fel-Pro 1204 gaskets are the way to go for better sealing, especially between intake ports (where I'm thinking the gaskets may have failed). I would appreciate any comments as I certainly don't want to do this again anytime soon. Thanks everyone for your time.

Yesterday I got the manifold off and have included pictures of what the gaskets look like now, pretty ugly for sure. It looks like movement has destroyed them, especially on the driver's side. The only difference there is that the alternator mount uses the front most manifold bolt. Could this have induced additional vibration and moving? Anyway, I darn sure won't use these gaskets again! Appreciate any observations/comments/recommendations.

 

I had a similar issue when I had these large port runner aluminum heads and was using an
old school offy intake with much small runners. I had to use non-neoprene gaskets to fix
the issue, but over time, the gaskets still want to "walk", creating a vacuum leak. Ended
up changing my head and intake to stock sbc. I did discover that there are 3-4 different
dimensions for intake gaskets, too.

 

I’ve never seen gaskets look like that. Even though the intake runners aren’t huge, it look like a FelPro 1205 (from what I see on the inside runners) might be an option.

 

Looking at the lower end of gasket it would seem mating surfaces are not parallel?

 

It looks to me like there was not enough clamping force to keep them from wandering around. It might take a little more than 20 lbs/ft. to do so. Gonna have to look at mine now.

 

Was this car running fine and then stored for a while?
Or running fine at first and then gradually got worse?
Or some other progression of cir***stances?

 

Has the block or heads been decked?
It may have changed the angles and the manifold does not sit correctly on the heads.

 

That is bizarre ... in this pic the gasket has moved so mush it has elongated the middle bolt holes in the gasket, that is how much it has moved/been forced out. My guess is the head surface and the manifold surface are not parallel to each other but I could be wrong. If you can verify the surfaces are parallel and there isn't any machining needed, I'd use Gasgacinch on the entire gasket, both sides before installing a new set. Also, make sure the head and intake surfaces are C L E A N. I usually wipe stuff down with lacquer thinner to make sure all the oils etc are removed.

I have never had or seen an intake gasket move like that. If the heads and intake surfaces are parallel, my guess is the intake was never torqued correctly but that is just a guess, I really have no idea what happened here ...

 

I actually wondered if the heads have been angle milled at some point in their life

 

Brings up another thing, if a used intake, maybe lay a good straight edge along it and make sure it’s not warped.

 

Here is from a Hamb post, similar issue back in 2006....

Your heads (I believe your using 200cc/72cc - only one that uses #1205) are bigger than your manifold can handle. Like listed above, you need to upgrade your manifold now to match the heads.

Port:

Dart 200cc/72cc = 1.14" x 2.00" (from Dart site)
#3700 = 1.14" X 1.88" (Edelbrock site)
Your head port is taller by = .120"
I believe the POS (silicone bead) is .060" wide on the 1205, you may
see this bead hanging out after torqued.

#1204 = 1.23" x 1.99"
#1205 = 1.28 x 2.09"
#1256 = 1.23 x 1.99"
stock typically 1.87" = which your #3700 is a direct replacement for the stock manifold.

Ports are usually "lengthened" towards the V/C, so ports can "hang out" causing vacuum leaks. Try as a quick test spraying carb clean or starting fluid along the top of the edge of the gasket (Don't spray into the carb/air cleaner as you go). If the RPM changes near a bolt or port there's your leak.

Based on this, I think it's just a parts miss match, not a cheap Fel-Pro gasket.

Hope this helps,
Later.

 

To check for mounting surface parallelism you could clean the mounting surfaces and snug one side of the manifold at a time to the head and check the end gap between the manifold and the block for a parallel gap.
If your Offenhauser manifold has small ports like mine you may also want to take the gasket and lay it on the manifold to see if you have adequate clamping surfaces.

 

I don't think the intake was torqued correctly and ,or is warped. I have never seen a Fel-Pro gasket that out of shape.

 

I always thought....(duh!)...that Fel pro was benchmark in gaskets. Cometic for specialty stuff.
Maybe upset the gasket area with a sharp punch and.... use the dreaded Indian Head Gasket Shellac and hope you won't need to swap gaskets in the future. (That stuff is GLUE!)
IF the OP indeed torqued the intake down like he shoulda and this junk happened...
maybe Fel-Pro had a bad batch of gaskets slip thru inspection!?

 

Chuck -

Are you using the "prescribed" torque method ?
Center - out and in a criss-cross (side to side) pattern ?

It somewhat appears in your pictures that you are torquing one side, then the other. One side is almost good/but usable, the other side...not so much ! This normally does NOT work well.

I would NOT suggest using RTV, except at the ends. Gasoline WILL eat (soften it, turn it to much) RTV.
Various Permatex works well, rubber cement works well, Copper Coat works well, Hylomar works well. As you are doing, only bond to the cylinder head.
Use a sealer (from above) around the intake openings, and some RTV at the ends of the manifold, and around the water openings if you like.
Let the sealer fully set around the inlet openings, before you place the manifold, then add the RTV at the ends, then carefully set the manifold in place.

1 - Put all fasteners in place.
2 - Set all fasteners by hand.
3 - Lightly snug all fasteners, verify they are evenly snugged.
4 - Torque to 20lbft. evenly, from the center working your way toward the ends, and continue to swap back and forth, from side to side at each fastener location.
5 - Double check the torque, using the same center to end - side to side pattern.

Cross fingers !!

Mike

 

First for me also

In p*** I have had to use different thickness to correct milled / decked heads block intake , also @ times to line up ports equally & slot bolt holes .
I do not think Felpro has a full listing by
#s on line like the older master catalog did

 

Wow, so I spent an hour doing a reply to all the comments and I wasn't smart enough to make sure I copied it and it appears I lost it. It said there was an ERROR. I do appreciate all the comments, but it will be tomorrow before I'm in the mood to do it again! A couple of pictures of the engine are posted today for reference. Talk with you later.

 

You mentioned that you torqued intake bolts to 20 ft-lbs, and Trick Flow recommended that. On their website, they show torquing pattern, and tell one to use the manufacturers recommended torque. I think I'd increase to 25-30 ft-lbs.

 

I was kind of wondering the same thing. I am running the same gasket on Trick Flow Twisted Wedge heads with a Holley Contender intake that I screwed on in '98. No problems to date. My guess is old intake and poor mating surface.

 

I have never see this before, either.

I have always torqued the bolts on an SBC, with an aluminum intake manifold, to 20lb.-ft. on the first p***, and then to 35lb.-ft on the second p***.

 

Damn right. I have been torqueing them to 35 ft lbs. for decades, cast and aluminum.

 

i think a dry fit and some feeler gages are in order

 

From the suggestions I've seen here, I would first try a dry fit to be sure the mating surfaces are tight.
If everything p***es, re***emble with torque bolts 20 lbs. on first p*** and 35lbs. on second p***.

I've added nothing new here, just stating that these suggestions make sense to me.

OP, how do you plan to proceed?

 

I just found something interesting in another thread on this site. Seems the owner (of the engine mentioned in the other thread) had purchased 12pt aftermarket intake bolts and they bottomed out in the aftermarket heads.

Bolts too long would explain reaching torque during install and failed gasket due to it not actually getting compressed. The solution ... washers on intake bolts.

 

^^^^^
That would explain the issue
""bolts to long""
Op Another thing /procedure is to
Snug all bolts equally in torque sequence , make 2-3 p***es before final
Torque,
Wants You done this many times you will get a fill for

 

I’ve never been able to get a TW on all Chevy (BB or SB) intake bolts.
How are you guys doing it?

 

I have never used torque wrench on intakes to heads ,Except to torque a roots Blower/ supercharger to intake ,7/16 bolts need
10 -15 FPs

If you feel the need of Torque wrench
You can use offset crows / boxed

 

Oh, I’ve never used one. That’s why I asked. The first intake manifold I did a change on, I took my truck to a friends house. I was 16/17 he was a bit older but had been at things for a long time. After getting ready to put the new intake on, I reached in my pickup and was proudly displaying my TW. He said “wtf are going to do with that”?
My first hint should have been I couldn’t use a socket on all of bolts to remove them. Lol.

Edit: wouldn’t that tool modify a torque setting?

 

there is a need to use a Torque wrench on many things , but to me this is not one ,
About 25ish years ago I visited a guy,
I was asked to ***emble a compleat long block engine sbc DD , No torque wrench was available, I did ***emble & was confident of knowing the feel of different torques , Im not saying its correct way to do but I did & there was no issues

 

For lawn mowers and dirt bike engines I never had a TW. Something about a vehicle engine, changes my mind.
But ya, on an intake manifold, I found out quickly 45 years ago, can’t do it. But like anything, it takes a while to get/learn a “feel “. But as many nuts and bolts I’ve wrenched on, I wouldn’t trust my feel for rod and main caps
on a vehicle engine.