Hardened Washers, BB Alum. Headbolts

[Wayne M.]

Looking at the P&A catalogs, I see that there are no special length headbolts (24 long and 8 short for both heads), in spite of the thick hardened washers [#3899396] required for each bolt, and the thicker head gasket. Pic shows one loose on a bolt and the other washer beside a bolt hole.

Unless the bolt-to-head interface is machined to compensate, I would think that there are at least 2 or 3 threads less bolt engagement in the cast iron block, as opposed to iron heads.

Any thoughts ?

[Clem Z.]

Re: Hardened Washers, BB Alum. Headbolts

Looking at the P&A catalogs, I see that there are no special length headbolts (24 long and 8 short for both heads), in spite of the thick hardened washers [#3899396] required for each bolt, and the thicker head gasket. Pic shows one loose on a bolt and the other washer beside a bolt hole.

Unless the bolt-to-head interface is machined to compensate, I would think that there are at least 2 or 3 threads less bolt engagement in the cast iron block, as opposed to iron heads.

Any thoughts ?

i have built a lot of BBC with aluminum heads and stock length head bolts with the hardened washers with no problem. i built one using longer than std head bolts and i had problems with certain head bolts on the lower side bottoming out in the block and causing a blown head gasket

[Joe L.]

Re: Hardened Washers, BB Alum. Headbolts

Looking at the P&A catalogs, I see that there are no special length headbolts (24 long and 8 short for both heads), in spite of the thick hardened washers [#3899396] required for each bolt, and the thicker head gasket. Pic shows one loose on a bolt and the other washer beside a bolt hole.

Unless the bolt-to-head interface is machined to compensate, I would think that there are at least 2 or 3 threads less bolt engagement in the cast iron block, as opposed to iron heads.

Any thoughts ?

Wayne------


I've wondered about this myself but GM never specified any different head bolts for big blocks with aluminum heads. They did, however, specify different head bolts for 1969 ZL-1.

I've also postulated the possibility that the bolt seats in the GM aluminum heads were machined a little deeper to compensate but I've never confirmed that.