67 BB Head Bolts

[Joe L.]

Re: 67 BB Head Bolts

Doug,

Thanks for those details. I was looking at the ARP bolt kits and noticed the washers. Had me wondering if they were necessary on cast iron head or only aluminum heads.

Daniel.

Daniel-----

The ARP head bolts (their kit number 135-3601) are flanged head bolts, just like originals. Therefore, the flat washers should not be required. However, I would check to be sure the bolts which thread into the blind tapped holes are the same length as stock GM. If not, they may need to be shortened by the thickness of the flat washers.

[Joe L.]

Re: 67 BB Head Bolts

All------

Later GM SERVICE big block head bolts OF THE ORIGINAL PART NUMBERS had a very different head design. Attached are photos of later SERVICE GM #3877668 big block LONG head bolts. This is the same part number used for all 1965-74 big blocks except ZL-1. These SERVICE bolts are quite old but do not date back to the 1965-74 period. The original bolts had a 5/8" across-the flats head size, a thin flange, a raised head periphery ("indented head") and a "cross" which extended nearly all the way to the raised periphery. The SERVICE bolts had a 9/16" across-the-flats head which was taller than the original bolts. Also, a slightly thicker flange, no raised periphery, no "cross" and a totally different head embossment.

The other bolt in the photos is a GM #3952331. This is the short bolt used for ZL-1 engines. It is 2-1/2" OL as opposed to the GM #3877669 short bolt used for all other big block engines which was 2-1/8" OL. This is an "ancient" NOS piece probably dating back to the original manufacturing run. It has a head design very similar to the other original big block head bolts except that it does not have a raised periphery.

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