1967 427 Exhaust Manifold Bolts

[Joe L.]

I'm curious as to what folks have found on original 1967 427's as far as the exhaust manifold bolts are concerned. I believe the use of the "locking thread" bolts, GM #3909821, began sometime during the 1967 model year, if not from the outset of the model year. French locks were not used with these "locking bolts". It's going to take known original cars to determine this with any hope of accuracy because I believe that many cars have been retrofitted with french locks and, possibly, standard bolts in order to make them "correct". Even if the french locks have been added, the original "locking bolts" might remain.

One way to check for the bolts without removing them is to just check for their flanged head configuration. Most of the exhaust manifold bolts are trimmed (non-indented) non-flanged hex head. The "locking thread" bolts were used only at the end positions on either side.

Why do I think the "locking thread" bolts were used for 1967?

1) GM says they were;

2) The part number is consistent with a part number that would have been released for the 1967 model year.

So, why so many 1967 cars with french locks? Well, french locks are "one of these things that everyone wants to think their car came with". So, after all these years of Corvette restoration, they may have created their own reality.

[Rick G.]

Re: 1967 427 Exhaust Manifold Bolts

Joe,

I am the second owner of a May 1967 built 427/435 hp car. The car still retains it's original Oct 1966 cast and built JA (California smog) engine. It has the original french locks.

I am still waiting to hear the rumble of your ZL1.

Best regards,
Rick

[Douglas L.]

Re: 1967 427 Exhaust Manifold Bolts

Joe,

I have a 1967-390hp Northern Californina car of which I am second owner. The block is stamped T0216IM. The motor has never been out of the car. All of the exhaust manifold bolts are non-flanged. The original french locks and spacer washers are still present on the ends of both exhaust manifolds.

I have a question on the use of flanged bolts. If they were used on the manifold ends, how would they work with the space washers? Would the bolts would have to be shorter in length than the non-shoulder bolts?

[Joe L.]

Re: 1967 427 Exhaust Manifold Bolts

Joe,

I have a 1967-390hp Northern Californina car of which I am second owner. The block is stamped T0216IM. The motor has never been out of the car. All of the exhaust manifold bolts are non-flanged. The original french locks and spacer washers are still present on the ends of both exhaust manifolds.

I have a question on the use of flanged bolts. If they were used on the manifold ends, how would they work with the space washers? Would the bolts would have to be shorter in length than the non-shoulder bolts?

Douglas------


I have no doubt that these french locks and bolts are original to the car.

No washers were used with the flanged head locking bolts. In fact, washers are rarely used with flanged head bolts of any kind.

The locking bolts used for the exhaust manifolds were shorter than the other bolts. The locking bolts were 1-3/16" whereas the other bolts were 1-1/4".

[Mark E.]

Re: 1967 427 Exhaust Manifold Bolts

Douglas,

Nice engine. I strongly urge you to replace the rubber fuel line and filter that's between the pump and carb and replace it with an original style all-steel line. The current set up is a fire hazard. I personally know of three cars which caught fire because of this modification (one was my high school Impala).

[Gene M.]

Re: 1967 427 Exhaust Manifold Bolts

Douglas,

Nice engine. I strongly urge you to replace the rubber fuel line and filter that's between the pump and carb and replace it with an original style all-steel line. The current set up is a fire hazard. I personally know of three cars which caught fire because of this modification (one was my high school Impala).

Mark makes a good point for anybody reading this. Let it be known a rubber hose on the pressure side of the pump is asking for problems. Also a clamp with a cut off tube and not bubble flared is not safe neither. Don’t do it, there is nothing for the clamp to lock against.