For all the gearheads out there

[hillegom]

So how does that happen Greg, faulty install?
Yet it worked all this time, and fails now?

[gregzz4]

Can't for sure say why it failed
All I can think of is it slipped down a bit during the install, and the gasket ports are 'just' a bit big, allowing it to find an edge of the head
Then over time it failed

This last set of gaskets was on there for 2-1/2 years without issue 'till the middle of October, so go figure

I checked the intake with a straight edge and all is good
I checked the intake bolts before removing and all was torqued

No explanation here, but I'm just a hack with this stuff

As I stated earlier, I used some 'poop' this time to keep the gaskets centered over the ports and expect this to work

[sirruckus]

glad to hear you found the problem - at least its relatively easy fix

[gregzz4]

One other thing that comes to mind is while I was sitting in air care at the end of August and she got warm for about an hour maybe that allowed the intake manifold the warp just a slight bit and gave room for the gasket to crack
Then when I put the distributor back in last weekend I got it off by one cylinder and it backfired a couple times
This may have blown the gasket out when it was originally only cracked
As I said I can't say for sure

[hillegom]

Well, your troubleshooting skills rock!

[SanguinesDream]

Those are pressure cracks so it either was when she got hot (not likely) or over torqued. Although the original cast exhaust manifolds will bolt on and will work fine, the manifold openings should be ground on the top sides to match the ports on the heads, or this will just happen again regardless of the "poop" used, no?

But at least you isolated it. Way to go!

[gregzz4]

Thanks guys !!

The intake and heads are aluminum so the gaskets were torqued to 25lbs both last time and this time. I started at hand tight, then 15, 20 and finally 25 twice
The port openings on the head are less than an 1/8" taller than the manifold
I think it's the gaskets being a smidge too big for the application and not getting enough purchase on the inner of the ports

I hope it's the last time I have to do it but as I said if it's an issue again, I'll get the factory gaskets from GMPP