�66 small block head bolts; ones visible to a judge

[Gary B.]

Thanks,


Gary

[Joe L.]

I know there are a total of 34 head bolts on a ‘66 small block, and only 16 of those, the ones on either side of each spark plug, are visible with the valve covers installed. Am I correct that the visible head bolts are all GM 3704796, which are the ones that are 1 3/4” long?


Thanks,


Gary

Gary------


Yes, GM #3704796 is the original part number for the bolts you refer to and they were 1-3/4" in length.

By the way, this is a very old part number which dates back to 1955 and was used through 1982 and beyond. These bolts have a trimmed (i.e. "non-indented"), non-flanged head with a raised circular headmarking. They are black-phosphate finished. There are often various manufacturer's ID marks in the center.

3704796 was discontinued in March, 1986 and replaced by GM #14082315. The latter was discontinued in November, 1996 and replaced by GM #10168527 which remains available to this day. The 14082315 were very similar to the 3704796 except that the threads were pre-applied with sealer and there was a very slight difference in the circular headmarking design. The 10168527 are substantially different. These bolts have an un-trimmed ("indented"), FLANGED head and are zinc plated. They also have the pre-applied sealer. It took 41 years but GM finally got it right; these head bolts should ALWAYS have had a flanged head. However, the change to a flanged head was probably most influenced by the shift to aluminum heads.

[Gary B.]

3704796 head bolts for the rebuild of my motor. I’ll have the engine builder use the NOS ones since they are visible when judged, and use ARP head bolts for the non-visible ones.

While I have you, I found two different part numbers for the ARP head bolt sets, and I can’t figure out how they differ. The descriptions on Summit and Jegs of the two sets sound identical to me; the ARP part numbers are 134-3601 and 134-3602. The latter cost about 5% more; $92 vs $97. Does anyone know how those two ARP sets differ?

Finally, here’s an example of the superseded, GM-discontinued 14082315 head bolts. You can see the thread sealer and you can see that the headmark is not typical for C2, at least based on the C2 bolts I’ve seen.

8229762D-35F8-4A84-BAFA-C2BDD4B8BE17.jpg

Gary

[Joe L.]

Thanks Joe. I’ve managed to collect enough NOS examples of the 3704796 head bolts for the rebuild of my motor. I’ll have the engine builder use the NOS ones since they are visible when judged, and use ARP head bolts for the non-visible ones.

While I have you, I found two different part numbers for the ARP head bolt sets, and I can’t figure out how they differ. The descriptions on Summit and Jegs of the two sets sound identical to me; the ARP part numbers are 134-3601 and 134-3602. The latter cost about 5% more; $92 vs $97. Does anyone know how those two ARP sets differ?

Finally, here’s an example of the superseded, GM-discontinued 14082315 head bolts. You can see the thread sealer and you can see that the headmark is not typical for C2, at least based on the C2 bolts I’ve seen.

[ATTACH=CONFIG]110186[/ATTACH]

Gary

Gary------


The ARP 134-3601 is the set you want. The 134-3602 is for 18 degree Brodix heads.

[Gary B.]

[Gary B.]

[Joe L.]

Joe,

One more question. I know my original GM head bolts don’t use a washer, but the ARP set comes with washers. Is there something about the ARP bolt technology that requires the use of a washer?

Gary

Gary------

No, I believe it's just that ARP recognizes that non-flanged head bolts should be used with hardened washers. GM finally recognized that in 1996 with the release of the flanged head bolts (the equivalent of using non flanged head bolts with a washer).

When I use GM head bolts I use them with hardened washers although I recognize that I'm losing about 1/8" of thread engagement.

The washer (or flanged head) spreads the clamping force over the entire machined head bolt seat on the head and not just the very small seating ring of a non-flanged head bolt.

By the way, big block head bolts were always flanged head design. So, for big blocks, GM got it right from the get-go.

[Gary B.]

[Gary B.]

GM 14082315 head bolt.

328B7722-474E-4169-AAFC-1CD424100FA9.jpg

It could be Highland Bolt & Nut Division of MNP Corp.

3F2103F4-D69A-4D96-BFD5-1C3A1AAD682B.jpeg

Not exactly the same, but close.

Gary

[Joe L.]

Joe,

I guess I’m missing something. Since the ARP 3601 head bolts have a flagged head, why does ARP include the washers? The washers seem redundant if the bolts have flanged heads.

Gary

PS Maybe I answered my own question. The ARP washers are described as hardened, parallel ground, so maybe the washers add something extra that the flanged bolts don’t have by themselves.

Gary------


The ARP head bolts have a reduced wrenching size compared to the GM bolts. The flange essentially makes up for the difference making the ARP bolts about the same as the GM as far as far as the contact surface goes. The GM flanged head bolts have a greater flange OD and are used without washers. The ARP system is much better, though; the use of their bolts with the hardened and ground washers is superior to the GM flanged head bolts.

[Gary B.]