[chiphead]

Looks like the block was decked. Have you talked to the builder?

I agree with others that suspect detonation or oil consumption. Black carbon looks like excessive fuel and oil. The flaking may indicate detonation is blowing the carbon off the piston. Sometimes detonation unseats the rings and allows oil consumption. Then the oil causes more detonation and problems compound until it pops a gasket.

I would suspect a tuning issue, combined with possible overheating and possible oil control issues. Here is what I did in a similar situation:

Have heads cleaned up with a .005" skim cut, or whatever minimum the machinist can do.
Have valve guides and seals checked for wear
Clean up the piston tops with a brass brush
Go back with Felpro 1016 gaskets and good head bolts.

Re-evaluate distributor and carb tuning. I suspect over-advanced timing and rich carb.

I'd like full motor specs (compression, cam specs, deck clearance, fuel used, etc etc) for detailed analysis of what may be going on.

[STEELCITYFIREBIRD]

Is that a crack between valves in chamber with rust around Ex valve??
Top chamber in photo, toward left of center of valves?
....Agree, block lOOks to have been surfaced.

[NeighborsComplaint]

Were those used heads you put on an rebuilt shortblock?

Block surface looks too smooth to my eye, no "tooth" to hold the head gasket and it failed where clamping force is the lowest. It is badly carboned up. A super rich mixture can detonate in the ring lands and shatter a compression ring or worse. I've done that and blown a chunk of the piston between the lands right off the piston and took out the head gasket just like yours. Mine smoked like a crop duster, though.

[STEELCITYFIREBIRD]

You might want to look into the intake and exhaust ports for signs of moving oil.... or post pictures.
What type of valve seals do the heads have? O-ring in keepers and tin shields, positive seals?
What brand? of head gasket...it looks grey in picture, I don't know who makes one like that...recently.
Was the head bolt loose in that area during disassembly??
Pull lifters one by one and check for wear!

[67428HO]

Numbers matching motor and heads , new Ferrea valves , bullet cam 430 lift 214/224, q- jet built by a member here. Original head bolts. Idle never seemed great, even with small cam and qjet.

[67428HO]

Butler head gaskets

[67428HO]

It didn't smoke.

[STEELCITYFIREBIRD]

Those look like the "BEST" brand gaskets that Butler sells, not the Butler Gaskets.

I'd want the deck sufaces a smooth as possible, not "toothed".

You have a CHEGG on your hands;

did the gasket lift because it got hot?
or
did it get hot because the gasket lifted?

It may not smoke but oil in the chamber can fuel detonation.
If it doesn't have correct positive seals on at least the intakes, it's likely passing oil. Ferrea valves don't have groove for o-ring type seals.

That is the thinnest sealing area on both sides because of the adjacent exhaust valves and the chamfers placing on (early?) 67 & back blocks.

At least check the lifters for that cylinder, specifically the exhaust.

Do you have all the correct parts under the carb for the 67 only heat crossover..or better, have them blocked?

[chiphead]

How hot did water temp ever get? In my experience you've got to get the engine over 220-230F to risk hurting the head gasket between the center two cylinders due to heat alone.

My guess is a combo of mild/moderate detonation, stock head bolts and basic head gaskets resulted in a popped weasel. Running over thermostat temp, but not 220+ usually indicates a tuning, octane or cooling system issue.

I don't trust brass radiators anymore. When I swapped to an aluminum radiator, the temps dropped to 170-185 and stayed there with a 160 stat, even in 100F summer.

What is static compression and ignition timing curve?

["QUICK-SILVER"]

Originally Posted by STEELCITYFIREBIRD

Is that a crack between valves in chamber with rust around Ex valve??.

That does need looked at.

With a leaky gasket, combustion from #4 would have lit off #6 early in it's compression stroke. That would have made it run rough rough.



Clay

[Bruce Meyer]

Those exhaust valves look a little too white for me. I bet it was lean and detonation took out the head gasket.

[STEELCITYFIREBIRD]

Yeah, the rust and missing carbon is pretty telling of a, let's say.... "leaky crack" .

[chiphead]

Originally Posted by STEELCITYFIREBIRD

Yeah, the rust and missing carbon is pretty telling of a, let's say.... "leaky crack" .

I see it now, the vertical black line just to the left of the valves in the upper chamber. The surrounding area looks steam cleaned along with minor surface rust that should not be there. I would absolutely have that area of the head magged for cracks.

[STEELCITYFIREBIRD]

Mag both heads entirely, pressure test and check deck surface.... both heads, with valves out preferably. Check springs. Valve seats touch up?
Basically quote a valve job...if castings are good.
Sucks on fresh engine.

Head Gasket materiel coating remind me of DG gaskets, from a long time ago, materials have advanced greatly.