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I own 1969 L89 19437S721089. I recently purchased NOS cylinder heads dated 10/67. I noticed that 2 intake runners on each head have 1/2" threaded holes leading to a cooling jacket hole underneath. My original heads dated 12/68 do not have these threaded holes or cooling jacket holes. Same part number on the heads 3919842.... Any ideas from the people who might know????
Thanks, Larry Myers
Based upon your description, it's not completely clear to me what the holes are that you're referring to. The only holes that go through to the cooling jacket on these cylinder heads that I am aware of are the holes on the ENDS of the heads. Early versions of these heads (like yours) should have holes on both ends of the heads. Later versions have a hole on only one end. However, these holes don't sound like the ones that you're talking about.
The only drilled AND TAPPED holes found on the bottom surface of the heads were those usually installed on the 3946074 cylinder heads. These were 7/16-14 holes drilled into bosses on the first and third intake runners. These holes did not go through to the cooling pasages, though. These holes were installed to be used with ZL-1 engines which used 2 extra cylinder head studs on each side. I was not aware that these holes were ever installed on the 3919842 cylinder heads since these heads were never destined for use on ZL-1s. Someone could have added them later, even though the heads you have are NOS. Unless you purchased them is sealed GM boxes, there's no telling what may have been done to them over the years for who-knows-what reasons.
Lawrence -- Like Joe L.,not sure which holes you're refering to. I have an early set of 842's (6-19-67 and 8-24-67), so I can examine in more detail if you give exact coordinates. The only "holes" I see are on the ends of each head; the big 1" plug with a square center, and the 2 threaded holes for alternator brackets.
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