C1, C2, and C3 Small Block Oil Pump Bolts

[Christopher R.]

I'm installing an oil pump on a '62 327 Corvette engine.

The 1973 Chevy Parts catalog lists (Group 1.652) oil pump bolts as follows:

55-62, 3754998, 7/16-14 x 2 3/16 - hex lock
67-73, 3892678, 7/16-14 x 2

Why the difference? I don't believe there's any differences in these engines.

The bolt I thought was correct has a "castle" type head. Is that the "hex lock" to which the catalog refers? I don't see how this unusual head shape would provide any locking.

In all the pictures and engines I've seen, I've never seen a lock washer under the head of this bolt. That strikes me as odd.

What's so special about this bolt that it gets a part number and a listing in the Parts catalog as opposed to being banished to the fastener section? ARP considers it so special that they carry a stud and nut for this application. The Paragon catalog chides you to always replace this bolt.

[Joe C.]

Re: C1, C2, and C3 Small Block Oil Pump Bolts

Chris,

The shorter bolt is for the main bearing cap with relief cut into it in the area of the pump bolt. The longer bolt is for the caps with no relief. Not certain, but I believe the relief was cut in on later caps. Your '62 probably does not have the relief, and therefore needs the longer bolt.
Visual inspection of the cap will verify configuration.

Joe

BTW: the shorter bolt, used in applications requiring the longer bolt will work, but strength will be compromised. Bolt more likely to fail.
Long bolt, used in short bolt application will bottom about 1/2 turn too soon, and MAY NOT be easily discernable.

[Joe L.]

Re: C1, C2, and C3 Small Block Oil Pump Bolts

chris-----

My recommendation is to use the ARP stud for all applications. It will provide an extremely high quality fastening and allow full engagement of threads.

Also, no small block or big block Chevrolet ever used a lock washer on the oil pump bolt.