62 Intake leak

[Dan S.]

I need help with an antifreeze leak on my 62 327 intake manifold. The first intake I put on this engine leaked internally into #8 cylinder, the next one I installed leaks externally at the passenger side front coolant runner. The first intake was installed by the engine rebuilder (I supplied intake, numbers matched) and after the engine sat over the winter I started it up and white smoke puffed out the right bank exhaust. The second intake I installed (this intake originally mated to the heads but does not having matching numbers), I made sure all surfaces were cleaned, intake gasket (FelPro) was glued to heads with gasket tack and set overnight. Intake was lowered gently onto heads, all bolts were torqued from center outward with a torque wrench. This intake leaks at the intake gasket externally without any pressure on the cooling system. What am I doing wrong? What is the torque spec for intake bolts? Do the intake manifold bolts have to have sealant on them?
Your help would be appreciated.
Dan Schall

[Dan S.]

Re: 62 Intake leak correction

I made an error on my previous post, It should read intake manifold instead of my first cylinder head. Sorry for the confusion.

[Kent D.]

Re: 62 Intake leak

Use silicone around the four water ports on both sides of the intake gaskets.

[Bruce B.]

Re: 62 Intake leak

The best sealent in my opinion is Permatex #2 Form a Gasket. Used it on my 340 HP 62 17 years ago and it is still there.
The Motors Manual 1962 edition call out for 25 to 35 foot pounds for the 327 intake manifolds.
Good Luck.

[William C.]

Re: 62 Intake leak

Yes, sealant on the threads of the intake bolts can be helpful. As can following the torque sequence in the ST-12 exactly, and in steps, I use 50%, 85% and 100% all in the recommended sequence.

[Stuart F.]

Re: 62 Intake leak

Can anyone address the root cause of his leak? My experience with intake manifolds reminds me that if you take all the usual precautions to use good quality gaskets and position the end seals right, and use a little sealant around the coolant passages, you should not be experiencing any such leaks, specially coolant. I've seen people even crack an ear off an end from over tightening and still not have a leak. Something tells me there is something else amiss; perhaps the heads were trued (milled), or the intake manifold, or both? Even if the manifold was moved slightly into position, it's usually the end seals that may get misaligned (service manual calls for use of a wood dowel in the distributor opening to guide manifold into place [?]).

Just a thought.

Stu Fox

[Kent D.]

Re: 62 Intake leak

Can anyone address the root cause of his leak? My experience with intake manifolds reminds me that if you take all the usual precautions to use good quality gaskets and position the end seals right, and use a little sealant around the coolant passages, you should not be experiencing any such leaks, specially coolant. I've seen people even crack an ear off an end from over tightening and still not have a leak. Something tells me there is something else amiss; perhaps the heads were trued (milled), or the intake manifold, or both? Even if the manifold was moved slightly into position, it's usually the end seals that may get misaligned (service manual calls for use of a wood dowel in the distributor opening to guide manifold into place [?]).

Just a thought.

Stu Fox

The root cause IMO is corrosionon on the intake manifold around the water ports. The end seals will only leak coolant.

[Stuart F.]

Re: 62 Intake leak

Kent;

By "end seals" I was referring to the rubber strips used at the front and rear of the valley (block to manifold) which I always assumed were there to prevent oil seapage from the valley. Granted the end seal portion of the actual "head to Manifold" gaskets are coolant passage seals and, as you say, therein may lie his problem due to corrosion. Would you be talking about manifold corrosion or heads (?). I suppose either aluminum or cast iron manifolds could corrode enough to cause a sealing problem. I have seen aluminum manifolds at swap meets that were terribly pitted around the coolant passages and the thermostat housing, specially dual quad manifolds as I've always have a special interest in them.

Stu Fox

[Kent D.]

Re: 62 Intake leak

I meet to say the end seal will not leak coolant.

[Dan S.]

Re: 62 Intake leak

The best sealent in my opinion is Permatex #2 Form a Gasket. Used it on my 340 HP 62 17 years ago and it is still there.
The Motors Manual 1962 edition call out for 25 to 35 foot pounds for the 327 intake manifolds.
Good Luck.

Thanks so much for your help.Dan Schall

[Dan S.]

Re: 62 Intake leak

Yes, sealant on the threads of the intake bolts can be helpful. As can following the torque sequence in the ST-12 exactly, and in steps, I use 50%, 85% and 100% all in the recommended sequence.

Thanks so much for your help, but what does ST-12 mean?
dan schall

[Joe R.]

Re: 62 Intake leak

Both John Hinckley and Joe Lucia on this forum have previously recommended using a thin layer of RTV, such as Permatex Ultra Copper, around the four water ports on the heads, on both sides of the gaskets. The RTV is *not* recommended for the remainder of the intake gaskets.

I think that the RTV goes a long way toward sealing surfaces that have mild pitting.

To keep oil from wicking up the intake bolts, I recommend coating the threads with Permatex #3.

It is possible that you have an alignment problem due to the heads and/or manifold being milled by some previous owner. Usually, the intake gaskets can accomodate a slight mis-alignment problem.

So, if last time you did not use RTV around the four water ports in the heads, you might try re-installing the manifold using that method to see if that fixes the problem. Also look carefully at the surfaces to see if there are obvious problems.

I recall seeing some nice photos from John Hinckley that showed the RTV applied and the wooden alignment guide in the distributor hole. Perhaps he will see this thread and post his photos again.

[Timothy B.]

Re: 62 Intake leak

There may be a problem from the heads being milled a few times over the years. The solution may be to install the manifold without the rubber end seals and use RTV in front and rear. This will allow the manifold to sit lower and seal. Other than that it's off to the machine shop.

[Joel F.]

Re: 62 Intake leak

Thanks so much for your help, but what does ST-12 mean?
dan schall

Dan, it is the factory service manual for early Corvettes. I forget the years it applies to, maybe 56-62? I'd consider it one of the most essential pubs for a C1 owner to have.

[John H.]

Re: 62 Intake leak

Here's the idea for the RTV (I use Permatex "Ultra-Copper") for the end seals and around the water ports at both ends, and my exotic wooden tool for guiding the rear of the intake straight down so it doesn't shift and smear the RTV off the sealing surfaces.