Davpmars

Hey guys,

I have a 68 corvette with a 1973 454 engine. I recently acquired some original 1968 exhaust manifolds but many of the plugs that fill the holes on each cylinder port are missing. (I assume these have something to do with California emissions)

I'd like to simply plug these holes. I've read that I should use a 1/4 - 18 brass pipe plug. (I'd rather use something black) What do you think? What is the best way to do this?

croaker

Headers

Faster Rat

Early C3s had smog pump systems.

69Vett

if you want something flush mounted you can use pipe plugs with allen head rececessed.
a little more difficult to locate than standard pipe plugs.

Davpmars

Is this stuff a standard thread? Could I pick up some standard pipe plugs at Lowe's or Home Depot?

7T1vette

Use standard Allen head pipe plugs. Then you can use a grinder to smooth them flush or just leave them as-is. Since you have the manifolds off the car, have them shot blasted, blow the dust off, wipe them down with lacquer thinner and give them two good coats of Seymour Cast Blast [super] hi temp paint (1600*F for exhaust manifolds). The paint will dry but will not be 'cured' until you drive the car and the engine runs at temp for a few hours. When curing, the paint will smoke some and will stink to high heaven! But, the paint will cure into a ceramic coating that will look just like fresh cast iron....AND NEVER RUST!!!

Great stuff. And you have the perfect opportunity to properly prep those manifolds so they will ALWAYS look GREAT !!

Easy Mike

Almost all 68s had AIR regardless of state of destination.

Davpmars

Sounds good to me! Is 1/4 - 18 NPT the right size plug? (I don't know what NPT stands for)

Big2Bird

National Pipe Thread Taper.

You can use pipe plugs, but the original ones, if I recall correctly, are more like a solid inverted flare nut. GM sold them forever, but no more.

68notray

A.I.R. holes are NOT pipe threads. Not not not not not pipe threads. In fact no fuel line brake line AIR line has ever been pipe threads. Doesn't work that way. The flare in the tubing is what seals, not the threads. If you want to correctly seal manifold AIR holes use a socket head set screw. I buy them at a big local hardware store. The tpi, or threads per inch is wrong also on a 1/4" npt. That's why they screw in about 1 full turn then bind up. If you force it, now you'll never get the correct one in. The correct "plug" will thread in smoothly all the way down then seal against the seat.

Duane4238

Listen to 68notray. He's right. The flare seals against a seat in the bottom of the hole. You can fill the holes with a set screw and some Loctite.
Duane

7T1vette

Don't know of any Loctite that will hold up to 1500*F+. Just put in the 'plug' (whatever type is needed). Snug it down tight and it should seal fine. I might have suggested using some JB Weld stick epoxy...but I don't know if that will hold up to the heat, either.

Big2Bird

GM and Dorman made them. They looked like this:

https://www.summitracing.com/parts/aaf-all50183

Bikespace

I found these on Eckler's sister site, $12- for a set.

http://www.rickscamaros.com/camaro-e...1967-1981.html

I'd seen individual "correct" inserts for sale for $18- each, at which point you may as well replace the entire manifold.


Update: I've installed them, and they work. They are likely 1/4"-18 Straight Pipe Thread, as mentioned below.

riverracer au

my 1972 A.I.R. system was plugged with 1/4"-18 NPS (National Pipe Straight)
any hydraulics parts store will have them.

web info,
Both NPT and NPS have the same thread angle, shape, and pitch (threads per inch).
However, NPT threads are tapered and NPS threads are straight (parallel).
Both threads have a 60° included angle and have flat peaks and valleys.