Exhaust manifold french locks

[David K.]

Hi guys,
First time posting, but have lurked here a fair amount. My question regarding french locks is were they installed on all engines both small block and big block as well as whether it came from Flint or Tonawanda? I have a 65 coupe 327-365 that was restored by a prior owner and french locks are installed which I think is correct. The real reason for my question is non Corvette. I have a 68 Nova SS 350-295 4 speed car that is an original car that the engine has never been out of. It still has the smog system in place, but there are no french locks on manifolds and does not appear to have been messed with at all. I know the AIM will not help as the locks or lack thereof would already be in place once it left the engine plant. Any thoughts on this? Or did only certain engines get the locks?
Any feedback much appreciated.

Dave

[William C.]

Re: Exhaust manifold french locks

1975 Parts book indicates that french locks were used on the outer ports of ALL smallblocks in all Chevrolet vehicles...

[David K.]

Re: Exhaust manifold french locks

Bill,

Thanks for the reply. Much appreciated.

Dave

[Keith B.]

Re: Exhaust manifold french locks

In 68 or 69 they stopped using them. Not sure when or why.

[Terry M.]

Re: Exhaust manifold french locks

In 69 for big blocks they stopped using them. Not sure when or why.

Fixed it for you Keith. Beginning in 1969 Tonawanda began using a bolt with deformed threads (a tri-oval shape) that actually dug into the cylinder head threads and needed no lock to secure them. I am not sure how that worked on aluminum heads, but that is a different story than the OP asked about.

David, It is probably unwise to become involved in any discussion that uses the terms "always" or "never" as it relates to Corvettes, or many other things in life.

[Keith B.]

Re: Exhaust manifold french locks

Thanks Terry I remember reading about the no French locks on the Chevelle forum but they did not say why. Now it makes sense with the new bolt. What about small blocks.

[David K.]

Re: Exhaust manifold french locks

Terry,
I've learned that with all cars and in particular Corvettes. LOL

Dave

[Terry M.]

Re: Exhaust manifold french locks

Thanks Terry I remember reading about the no French locks on the Chevelle forum but they did not say why. Now it makes sense with the new bolt. What about small blocks.

Joe Lucia has posted here several times about those tri-oval bolts -- including photographs. They are most easily identified in judging by their use of a head with a built-in washer and an un-clipped bolt head -- that is sometimes referred to as "indented head." I believe they are dark brown or black colored as well. Of course a dedicated and cleaver restorer can mimic what we can see of those bolts when installed, and a car with its original fasteners is likely to be deteriorated enough that at leas tthe finish will not be discernible.

So far as I know (for sure through 1972) Corvette small blocks got french locks on the outer two sets of exhaust manifold bolts.

David, The AIM will not help you in answering questions about french locks. Whether Corvette, Nova or trucks -- the engine was delivered to the vehicle assembly plant as an assembly -- so the Corvette, Nova or truck AIM will not tell you a thing about the details of that engine assembly. One of the most common and fruitless moves is to rely on the details of the illustrations in the AIM, but that is another story. I have some engine assembly materials (in most cases I hesitate to call the AIMS because they are different in both format and detail from the Assembly Instruction Manuals we are used to, but they are not complete and almost all for 1970-72 Corvette and none are for Nova or trucks.

Just to throw some "stuff" in the game there are some minor discernible differences between original french locks and most, if not all (there I go, getting close to always), reproductions.