picked up AIR injection in '76
Slant-6 heads with air injection ports were first released in '72. There were heads with and without the air injection ports starting in that year. Remember the California-emission cars got air injection (and a very primitive, non-valved EGR system) in '72.
and hydraulic lifters around '81-'82
1981. And while the '81-up head is different, it is interchangeable with earlier heads regardless of whether you're running solid or hydro lifters.
There wasn't enough difference in port shape or chamber size to say any one year is THE one to have.
True, though the '67-up heads have the better combustion chamber shape (revised that year for more complete combustion) and the pre-'75 heads w/spark plug tubes mean a much wider range of spark plug optionsincluding the NGK ZFR5N, which has a double-extended electrode set that moves the spark point closer to the middle of the combustion chamber and away from a quenchout zone. They are not gimmicky "magic" plugs, just a good design variant of a standard plug, originally designed for tough-to-light engines (desmogged AMC 232/258, Chrysler TBI 318s in '81-'83 Imperials), 'cause the mixture is much less variable in the middle of the chamber than at the edges, and these long-electrode plugs give more consistent light-off of the cylinder under borderline-combustibility conditions. The same extra-long electrode set is used in many late Mopar applications (3.5 V6, 4.0 I6, etc.), and they work very well in slant-6s.
Remember to remove the metal ring washer from the spark plug before installing it in a '63-'74 head.
I would fix the broken stud for now
Yup. If you take your time and think ahead, it shouldn't be much of an ordeal. If you get impatient and do something like break off an "Easy Out" (hah!), you're in for a much harder task. If you wind up having to drill the stud hole oversize, you can get a stud with bigger threads on one end and smaller on the other. Dorman #675-097. It has 3/8"-16 threads on the head side, and the stock 5/16"-24 threads on the manifold side. Overall length is a little shorter than the 675-092 standard replacement stud, but that's of no consequence. That's what I wound up successfully using at the end of a long comedy of ignorant errors and dumb mistakes* a long time ago on my '65. All you have to do is overdrill the hole straight and true. Head on engine: Not a problem. Manifold on head: Not a chance.
Use Loctite (not RTV or teflon tape) on the head-side threads, which means you need to clean the coolant and tapping oil out of the overdrilled head hole using something (alcohol or brake cleaner, e.g.) that won't leave a residue. The head threads are 7/16" deep on the 675-097, while the original-type 675-092 has 9/16" of head threads; if you're careful and mark your tap accurately with a loop of masking tape, you can make (leave) a ledge at the "bottom" of the overdrilled head hole to bolster stud seating and sealing.
*-involving a hammer drill, "EZ-out", jigsaw, tap extractor, JB-Weld, Plexiglas heater, and assorted other inappropriate tools and supplies
keep an eye out for a '72 or newer head
Meh. I wouldn't turn down a '67-'71 head. The factory induction hardening is not very deep; it's standard practice to install hard exhaust valve seat rings during a good head buildup, anyhow.
Handy chart listing slant-6 hard part variants (most, but not all) is
here.
And welcome back, Grumpus.
we broke the rear manifold bold off and took it to the machine shop and had it tanked and shaved a little just for piece of mind. he threw in a new stud for free. it has solid lifters and had to adjust the valves (i do it while its running) not sure about the seats tho.
