389/421 1964-66

Pontiac V8 389/421 1964-66

Early Castings, Early Problems — 389/421 1964-66 for Pontiac V8s

The 1964-66 389 and 421 heads are early Pontiac castings, and the thing that sets them apart is not the valve, it is the rocker stud. These heads used pressed-in studs, and pre-1964 pieces oiled the rockers through the stud, which changes what you can bolt on and what the machine shop has to do.

Butler lists Ferrea valves specifically for 1964-66 389-421 heads, adjustable 5/16" guide plates for 326-389-421 castings, and 7/16 rocker stud upgrade and conversion kits built for 1961-1966 389-421 heads, alongside the cast iron guides, seats, seals, springs and locks.

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More About 389/421 1964-66

1. The Rocker Stud Is The Story

More work goes into the studs on these heads than into anything else, and Butler's own product notes are direct about it.

Converting press-in to screw-in	the holes must be drilled and heli-coils inserted for 7/16 threaded studs, and on 1961-1966 389-421 heads the stud bosses will need to be milled. Butler says plainly that this should be done by a qualified machine shop.
Thinner hex studs	Butler's early-head kit ships with the ARP stud that has a thinner hex, specifically because the stud boss has to be milled.
Through-stud oiling	certain pre-1964 heads oiled through the stud, and replacement studs do not have oil-through holes. On those applications use rocker arms and pushrods with an oil hole. Butler also plugs the block with two 1/8 NPT pipe plugs at the deck to keep oil away from the heads, though that step may not be mandatory.
An alternative	a press-in conversion stud with a 1/2" coarse base thread is also available for 389 and 421 heads, tapped to 1/2" rather than heli-coiled, and sized so factory valve covers still fit. Have a shop pull and tap the heads.

2. Valves And The Rest Of The Head

Valve length	Butler lists a 1.66" by 4.980" 45 degree exhaust valve specifically for 1964-66 389-421 heads, noting they are slightly longer than stock, paired with intakes in the same 4.980" length.
Guide plates	adjustable 5/16" guide plates are listed for 326, 389 and 421 castings, which is what you need once the valvetrain is converted to studs and guide plates.
Pushrods	the 389 and 421 share the shorter pushrod length with the 326, not the longer 350 through 455 length.
Guides, seats and springs	cast iron head guides in 11/32", a valve job, and springs rated around a 1.600" installed height matched to your cam.

3. Before You Start Cutting

These are old castings with limited material around the stud bosses. There is no generic torque spec for the studs because every head is different, and pre-1964 heads in particular can crack once the studs are out.

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