Fix one thing and there's another that pops up...

[Owen L.]

'67 427/390
New timing chain, new oil and filter, flushed the block for long-overdue coolant change... started it up today and now have puddles of coolant on both sides of the intake at the midpoint where the carb mounts. It was seeping up from the head side of the intake gasket; none of the 4 bolts were tight like the others. Cinching them down did nothing to stop the leaks, so: drained the coolant, pulled the intake off, scraped the old gasket from the heads and "china wall". Just a few drops of coolant in the lifter valley probably from when I lifted the intake off. No water under either valve cover.

Is intake gasket failure at this location indicative of anything greater than needing a new gasket (and torquing the bolts appropriately)?

What replacement gasket appears somewhat GM original?

Do any of the bolts require sealant on the threads?

Thanks in advance for all advice and recommendations.

[Owen L.]

Re: Fix one thing and there's another that pops up...

My searching seems to point to part #6259379 that has this appearance:
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Does this seem correct for appearance where it's visible after installation?

[Mike M.]

Re: Fix one thing and there's another that pops up...

i use a teflon based sealant, common to tool boxes of Plumbers, to coat the intake to head bolts.loctite makes such a sealant. mike mccagh

[Owen L.]

Re: Fix one thing and there's another that pops up...

i use a teflon based sealant, common to tool boxes of Plumbers, to coat the intake to head bolts.loctite makes such a sealant. mike mccagh

Like this stuff? I've got some from a bathroom remodel last summer.
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[Gary B.]

Re: Fix one thing and there's another that pops up...

Owen,

Different thread sealants have different max temperature limits and breakaway torque values. Loctite 567 is rated to 300 F. It also has a low breakaway torque. It’s not meant as a thread locker, so that aspect is OK for your application. I’m not sure how high the temperature goes near those bolts.

I think the Rectorseal 2 Plus 2 is rated to 125F or 140F, so good for house plumbing, but maybe not ideal for your automotive application.

Gary

PS Another choice of a thread sealant is Loctite 592, which is rated to 400F.

[Owen L.]

[Mike M.]

Re: Fix one thing and there's another that pops up...

Loctite 567 is the product i use. get the .2 fl oz tube as the lager tubes available are difficult , if not impossible to withdraw product from the larger tubes. mike mccagh

[Mark E.]

Re: Fix one thing and there's another that pops up...

Owen,

Continue investigating the source of the leak. There are no coolant passages in the center of the intake. Check the thermostat housing, upper radiator hose, heater hose connection, and coolant passages at either end of the cylinder head.

[Owen L.]

Re: Fix one thing and there's another that pops up...

Thanks Mark,
I've got the head surfaces scraped, holes chased, and overall cleaned up. I don't see anything out of the ordinary there. The intake is in an electrolysis tank to help clean it up. When I scraped the mating surfaces I didn't see anything odd but will check once it's cleaned and dried.

I can understand a crack in a head's water jacket but it would be really odd that it showed up as coolant on each side of the intake in the same general location. When I removed the intake, one of the casting chambers above the exhaust crossover was full of coolant and the other side had some coolant but not full. The lower chamber on one side was full of oil.

Do you know where the coolant passages run in the head?

[Owen L.]

Re: Fix one thing and there's another that pops up...

Does anyone know if the upper cavity in the heads over the exhaust crossover port come close to the cooling passages? The only thing I can think of is that coolant is coming into that cavity from the backside - but still odd that it would happen to both heads and appear at the same time.

[Mark E.]

Re: Fix one thing and there's another that pops up...

The two center intake bolt holes on each head pass through to the lifter valley. They are not near any coolant passages or jackets. So they can wick oil but I don't see them as a source of coolant even with a leaky head gasket or cracked head.

Is it possible the front intake bolts or thermostat housing is leaking and the fan is blowing the coolant back?

I'm not clear what you mean by "casting chambers above the exhaust crossover". Can you clarify or post a photo?

Screenshot 2022-03-21 123716.jpg

[Mark E.]

Re: Fix one thing and there's another that pops up...

Does anyone know if the upper cavity in the heads over the exhaust crossover port come close to the cooling passages? The only thing I can think of is that coolant is coming into that cavity from the backside - but still odd that it would happen to both heads and appear at the same time.

I just saw your post. Good question; I understand what you're saying. And you're right- it would be a coincidence for this to happen with both heads. I haven't seen this happen, but hopefully someone will chime in...

[Richard M.]

Re: Fix one thing and there's another that pops up...

These are 3904381(square port) BB heads but I believe a similar configuration of the exhaust crossover circuit on oval port 390hp heads. ONE of those intake manifold bolt locations is a blind hole. I don't recall if they bottom out into a coolant passage or not. IF they do, I suppose it's possible they could be damaged if extra long bolts were used overstressed the blind hole bottom areas.

It seems od that all 4 of your center bolts were somewhat loose. Is it possible the bolts are too long and bottomed out?

You may want to clean and inspect those 4 holes in the heads very carefully.

Intake bolt holes marked "B" are blind holes. Those not marked are open holes into the lifter valley and should be sealed. I use liquid Permatex Gasket sealer.
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BB valve guides are in the coolant passage areas. Guides are conically shaped. I've heard of improper guide installations where the guide is installed upside down and cracks the coolant passage area. It appears you didn't have any recent head work done, correct?

The only other explanation I would think of(reaching here though), for coolant puddled at the crossover area, would be if it traversed as a leak from the front water jacket mating areas of the intake to heads, then trickled its way by gravity and fan pushing it to the center area along the mating edge of the valve cover to intake rail.

One thing I always do, SB or BB, is to put a small bead of Hi-Temp RTV around the gasket mating surface on both sides at all 4 water jacket positions. Just a fail safe for rebuilds. I've never had a leak in all the years I've done that.

Rich

[Mark E.]

Re: Fix one thing and there's another that pops up...

These are 3904381(square port) BB heads but I believe a similar configuration of the exhaust crossover circuit on oval port 390hp heads. ONE of those intake manifold bolt locations is a blind hole...

Intake bolt holes marked "B" are blind holes.

Rich

Rich,

Are you sure about the blind hole? See my prior post with photo showing all center bolt holes going through to the lifter galley. Maybe square and oval port heads are different?

[Thomas H.]

Re: Fix one thing and there's another that pops up...

One thing I always do, SB or BB, is to put a small bead of Hi-Temp RTV around the gasket mating surface on both sides at all 4 water jacket positions. Just a fail safe for rebuilds. I've never had a leak in all the years I've done that.
Rich

Standard operating procedure here as well. Never had a coolant leak from the intake doing it this way.

I Forgot to seal the intake bolt threads on our race engine one time. Once after shutting it down from a break in, I noticed water bubbling slowly from around one of the front intake bolts next to the coolant passage. Removed the bolt and resealed (had to drain the water level down a bit) reinstalled - no more leak.

Good surface prep and a thin bead around the front and rear coolant areas is key.

Tom