69 L36 AIR Exhaust Manifolds

[Egil Askeland]

Need advice on safe removal of exhaust manifolds for sealing a small leak towards the block on one cylinder. Would prefer to temporarily plug AIR holes on one side. My concerns are :
Danger og breaking bolts in the middle of a good driving season.
Finding the correct plug / threads for blocking AIR holes.
Sealing manifold against block without gasket ?
I am a new member and have to appologize if all this has been discussed in detail earlier. Thanks, - Egil

[Joe L.]

Re: 69 L36 AIR Exhaust Manifolds

Egil-----

Generally speaking, the exhaust manifold retaining bolts do not present problems for removal. However, if your really concerned about breaking a bolt, just don't apply excessive force to remove them. Use a 3/8" drive ratchet which shouldn't allow you to apply enough force to break one of the bolts, even if the bolt has become brittle due to hardening. If you can't get them out with the 3/8" drive ratchet, then wait until the driving season is over to remove them. If the do break off, you will still be able to remove the manifold. The problem will be one of removing the bolt remnant from the cylinder head. This may require removal of the head to do properly.

The exhaust manifold should seal just fine against the cylinder head without the neat for any gaskets, at all, at the interface. The only thing that will cause a problem here is if the exhaust manifold is warped. Check these with a precision straight edge and, if necessary, have a machine shop surface the manifold mating flange.

The AIR fitings in the manifold are STRAIGHT thread for TUBING NUTS and NOT pipe thread as many folks assume. I believe that the thread size is 7/16-20.

[Joe L.]

Re: 69 L36 AIR Exhaust Manifolds

Egil-----

Generally speaking, the exhaust manifold retaining bolts do not present problems for removal. However, if your really concerned about breaking a bolt, just don't apply excessive force to remove them. Use a 3/8" drive ratchet which shouldn't allow you to apply enough force to break one of the bolts, even if the bolt has become brittle due to hardening. If you can't get them out with the 3/8" drive ratchet, then wait until the driving season is over to remove them. If the do break off, you will still be able to remove the manifold. The problem will be one of removing the bolt remnant from the cylinder head. This may require removal of the head to do properly.

The exhaust manifold should seal just fine against the cylinder head without the neat for any gaskets, at all, at the interface. The only thing that will cause a problem here is if the exhaust manifold is warped. Check these with a precision straight edge and, if necessary, have a machine shop surface the manifold mating flange.

The AIR fitings in the manifold are STRAIGHT thread for TUBING NUTS and NOT pipe thread as many folks assume. I believe that the thread size is 7/16-20.

[Egil Askeland]

Re: 69 L36 AIR Exhaust Manifolds

Joe,- Thank you very much for your valuable feedback !
I want to keep my car as original as possible,...would you suggest any form for external cleaning and coating of manifolds before machining sealing surface, ...if required, or is this a major job that is better done at a later stage ? Thanks again, - Egil

[Egil Askeland]

Re: 69 L36 AIR Exhaust Manifolds

Joe,- Thank you very much for your valuable feedback !
I want to keep my car as original as possible,...would you suggest any form for external cleaning and coating of manifolds before machining sealing surface, ...if required, or is this a major job that is better done at a later stage ? Thanks again, - Egil

[Joe L.]

Re: 69 L36 AIR Exhaust Manifolds

Egil------

The manifolds can be cleaned of all rust by bead blasting. However, they'll rust again rather quickly. Most of the commercial paints or coatings I've not found to be satisfactory for one reason or another, although some folks on this board have reported good results with a few. For permanent restoration I recommend sending them to Jerry MacNeish.

[Joe L.]

Re: 69 L36 AIR Exhaust Manifolds

Egil------

The manifolds can be cleaned of all rust by bead blasting. However, they'll rust again rather quickly. Most of the commercial paints or coatings I've not found to be satisfactory for one reason or another, although some folks on this board have reported good results with a few. For permanent restoration I recommend sending them to Jerry MacNeish.

[John H.]

Re: 69 L36 AIR Exhaust Manifolds

The air manifold tube nuts are what GM called "Straight Pipe Thread" (as opposed to NPT pipe threads, which are tapered); interestingly enough, that's exactly the same as 1/2"-20.

[John H.]

Re: 69 L36 AIR Exhaust Manifolds

The air manifold tube nuts are what GM called "Straight Pipe Thread" (as opposed to NPT pipe threads, which are tapered); interestingly enough, that's exactly the same as 1/2"-20.

[Egil Askeland]

Re: 69 L36 AIR Exhaust Manifolds

Thank you all for your good help. Removed manifold 3880828 safely as you described, but noted that 4 of the 8 bolts has a larger "washer area" integral with the bolthead.
- What is the correct bolt part #, and is it available from GM today ?
- Assume I should apply thread sealant GM part # ? when re-installing ?
- What is the correct torque for the 8 bolts ?
- I am looking for some good books covering the 427 engine, any proposals ?

[Egil Askeland]

Re: 69 L36 AIR Exhaust Manifolds

Thank you all for your good help. Removed manifold 3880828 safely as you described, but noted that 4 of the 8 bolts has a larger "washer area" integral with the bolthead.
- What is the correct bolt part #, and is it available from GM today ?
- Assume I should apply thread sealant GM part # ? when re-installing ?
- What is the correct torque for the 8 bolts ?
- I am looking for some good books covering the 427 engine, any proposals ?

[Joe L.]

Re: 69 L36 AIR Exhaust Manifolds

Egil-----

What you found is exactly how it should be. The bolts for the first and last runners are 1-3/16" in length. These bolts are a flanged head type bolt and are of GM #3909821. They're still available from GM and cost $1.77/each GM list.

The bolts for the 2 center runners are 1-1/4" long and used a standard, non-flanged head. They are GM #3736035 and they're still available from GM for $3.84/each.

Use no sealant on these bolts as none is required. However, you can use a little high temp anti-size compound. The torque on the bolts is 20 lb/ft. Don't overtighten!

[Joe L.]

Re: 69 L36 AIR Exhaust Manifolds

Egil-----

What you found is exactly how it should be. The bolts for the first and last runners are 1-3/16" in length. These bolts are a flanged head type bolt and are of GM #3909821. They're still available from GM and cost $1.77/each GM list.

The bolts for the 2 center runners are 1-1/4" long and used a standard, non-flanged head. They are GM #3736035 and they're still available from GM for $3.84/each.

Use no sealant on these bolts as none is required. However, you can use a little high temp anti-size compound. The torque on the bolts is 20 lb/ft. Don't overtighten!