This thread is giving me anxiety just reading it, remembering one such attempt of mine repairing my (long gone) 1988 F350 460cu. in. gas powered truck.
The truck developed a tick, then turnined into bad exhaust leak (smell it in the cab bad), due to two broken and missing exhaust manifold bolts.
It turns out that many V8's of that era are so inefficient and unburned hydrocarbons dirty, that they inject air into the exhaust manifold to form a secondary burn chamber, before the gasses move to the catalytic converter. That extra heat cracks exhaust manifolds and breaks bolts, so Ford upgraded the ones on this truck from cast iron, to cast steel. There was also a bolt upgrade (maybe a Ford service bulletin) to
titanium bolts, a dealer-only item.
The steel bolts were broken off about flush with the head casting, but the irregular surface of the bolt, at the break, had the drill bit wandering and me really making a mess of things, elongating the hole, and FUBARed the threads in the head. Despite days of soaking w/PB Blaster, I had to remove the manifold, breaking off more bolts in the process. I found with the manifold in place, and gravity working against me, the penetrating oil doesn't make it to the threads in the head, the path is too long. The same with a torch, the path too long, the mass too large, to get heat where I needed it, on the threads.
What (in my mind) should have been an easy fix, California truck, never seen salt, turned into me removing both heads. Then me removing some of the broken bolts myself, on the bench. In the interest of time, I had my local automotive machine shop repair the remaining 7-8 broken off bolts, in a fixture on their milling machine. The holes I FUBAR'd needed Timecerts thread repair inserts installed.
Then while the heads were off, I had the machine shop do a valve job. Because why wouldn't you? $600 machine shop bill, $200 worth of titanium bolts, $200 to have the steel exhaust manifolds ground flat (new ones were $1200), and tracking down special inconel-based, ultra high temp anti-sieze. New head gaskets, new air injection tube assemblies (the old corroded ones broke while removing them). busted knuckles and a wrenched back, $1500 later, I was on the road minus the ticking stinky exhuast leak, good times!
oh sure, it's funny NOW