What are known original exhaust manifold bolt headmarks for '66

[Gary B.]

The '66 TIM&JG is silent on the headmarks on '66 exhaust manifold bolts. I've seen bolts being sold that have a circle within a circle and others have have a H within a C within a circle. Does anyone know if either of these designs matches known original headmarks for '66 exhaust manifold bolts?

Thanks,

Gary

[Michael M.]

Re: What are known original exhaust manifold bolt headmarks for '66

Gary, my original exhaust manifold bolts (327/350HP) have a circle within a circle. Production date April 20, 1966. Hope this helps.

[Joe L.]

Re: What are known original exhaust manifold bolt headmarks for '66

Gary, my original exhaust manifold bolts (327/350HP) have a circle within a circle. Production date April 20, 1966. Hope this helps.

Michael and Gary-------


I believe that the "2 circles" is, by far, the most common headmarking for exhaust manifold bolts for C2 and, at least, early C3 small blocks.

[Keith B.]

Re: What are known original exhaust manifold bolt headmarks for '66

Joe are these bolts or the ones for BB still available from GM?

[Rich P.]

Re: What are known original exhaust manifold bolt headmarks for '66

Small block or big block??? Small block, double circles, F, A, N, TR, RSC, P, M, FP, C, C with 6 radial lines, Ch. I know I'm forgetting some. An iteresting side not is the horizontal trans mount to frame bracket bolt is the same as the short bolt and the long shifter to bracket bolt are the same as the long manifold bolt.

[Joe L.]

Re: What are known original exhaust manifold bolt headmarks for '66

Joe are these bolts or the ones for BB still available from GM?

Keith-----


The only bolts currently available from GM are the locking-type bolts used for the end positions on 1967-74 big blocks, GM #3909821. However, the headmarking on these bolts is not the same as original.

[Joe L.]

Re: What are known original exhaust manifold bolt headmarks for '66

An iteresting side not is the horizontal trans mount to frame bracket bolt is the same as the short bolt and the long shifter to bracket bolt are the same as the long manifold bolt.

Rich------


Yup. And that long bolt on the shifter will sometimes fracture or crack after long service. Folks should check this bolt carefully whenever they have it removed.

[Gary B.]

Re: What are known original exhaust manifold bolt headmarks for '66

Thanks everyone.

GB

[Doug J.]

Re: What are known original exhaust manifold bolt headmarks for '66

When you say "locking type bolts", would you be refering to a shoulder bolt. You also mention "the end positions on 1967-74 big blocks". End positions being the very last bolt on each side, front and rear of manifold, which would mean 2 bolts per side? Or front and rear exhaust runner, which would mean 4 bolts on each side, 2 on front runner and 2 on rear runner? Reason I'm asking is because I lost 4 points on Originality, with a notation of "shoulder bolts front/rear". As of now all bolts are are just a bolt head against the exhaust manifold, Manual states that no washers or locks are required. Car is an early (Dec,71 built) 1971 with a 454. If it does require a shoulder bolt front and rear, what do I do in the case of the bolt requiring a stud on the bolt for the A/C and alternator bracket. All comments and particularly pictures would be greatly appreciated. Thanks in advance for any help.......Doug

[Joe L.]

Re: What are known original exhaust manifold bolt headmarks for '66

When you say "locking type bolts", would you be refering to a shoulder bolt. You also mention "the end positions on 1967-74 big blocks". End positions being the very last bolt on each side, front and rear of manifold, which would mean 2 bolts per side? Or front and rear exhaust runner, which would mean 4 bolts on each side, 2 on front runner and 2 on rear runner? Reason I'm asking is because I lost 4 points on Originality, with a notation of "shoulder bolts front/rear". As of now all bolts are are just a bolt head against the exhaust manifold, Manual states that no washers or locks are required. Car is an early (Dec,71 built) 1971 with a 454. If it does require a shoulder bolt front and rear, what do I do in the case of the bolt requiring a stud on the bolt for the A/C and alternator bracket. All comments and particularly pictures would be greatly appreciated. Thanks in advance for any help.......Doug

Doug-----

The locking-style bolts have a special thread which achieves the same effect as a distorted thread lock-nut. A wrench has to be used to "take them all the way down"; they cannot be threaded-in by hand.

The locking style bolts were used on the end runners, both sides. So, there are FOUR bolts per side.

The locking style bolts which were used had a FLANGED head (sometimes called a "washer head"). The bolts used for the other positions were standard hex head. No washers were used for any bolts.

For bolt positions using studs (for peripherals attachment), specific studs replaced the bolts.

[Doug J.]

Re: What are known original exhaust manifold bolt headmarks for '66

Joe, Your last sentence has me a little confused, "For bolt positions using studs (for peripherals attachment), specific studs replaced the bolts."

Would the stud nut have a flanged head (alt. and a/c brackets mount to the end bolt on the front runners on both sides) or would it be just a plain nut that would be against the manifold, than the bracket, than a lock washer and nut. According to the 1971 AIM, the a/c side (UPC C60 sheet 4 page 324) seems to show a plain nut stud with a flat washer against the manifold, and on the alt. side (UPC N40 sheet A7 page 402) seems to show a plain nut on the stud, no washer against the manifold. All of the above is in referance to a 1971 LS5. Thanks for any insight....Doug

[Joe L.]

Re: What are known original exhaust manifold bolt headmarks for '66

Joe, Your last sentence has me a little confused, "For bolt positions using studs (for peripherals attachment), specific studs replaced the bolts."

Would the stud nut have a flanged head (alt. and a/c brackets mount to the end bolt on the front runners on both sides) or would it be just a plain nut that would be against the manifold, than the bracket, than a lock washer and nut. According to the 1971 AIM, the a/c side (UPC C60 sheet 4 page 324) seems to show a plain nut stud with a flat washer against the manifold, and on the alt. side (UPC N40 sheet A7 page 402) seems to show a plain nut on the stud, no washer against the manifold. All of the above is in referance to a 1971 LS5. Thanks for any insight....Doug

Doug-----

Sometimes the stud has an integral nut which is flanged and sometimes not. The GM #3928905 stud used for big block with P/S alternator bracket did include an integral nut which was a flanged type. I believe the GM #3828906 stud, used for the big block with A/C compressor bracket used an integral nut which was not flanged.

A tip: whenever a flat washer is shown under the head of a bolt, under the integral nut of a stud, or under a hex nut, it is extremely rare that the bolt, integral nut of a stud, or nut is a flanged type piece.

[Doug J.]

Re: What are known original exhaust manifold bolt headmarks for '66

Joe.....Part numbers and applications..on the money. Thank you very much.