Need to plug a hole...

Well, 6 holes actually.
On my 74 rig with the 258 motor I removed the air pump and air injection assembly. I don't want to get a different exhaust manifold yet so I need to plug up these holes. I don't want to cut the tubes on the assembly and crimp them shut either. The threads are 1/2" by 18 threads per inch. Having a rough time finding just a plain short bolt to plug the holes? Oddball bolt size/thread pitch combo.
What have you guys done to remedy this situation? Worse case I guess is to get some short pieces of tube to use in place of the little air manifold collars.

Edit: 1/2" x 18 threads per inch not 16tpi

 

There are plugs available, but I have not found a source for them. I don't think they are 1/2"-16. 1/8" black iron pipe plugs will work, but they don't go in very far and look cheesy. Supposedly a 9/16" NF bolt fits the threads - buy some and cut them very short. You may have to get them from McMaster-Carr or such, since your local hardware probably won't carry them. Supposedly some oil pan drain plugs fit too.

 

On the Chevy I welded the fittings shut and ground em flat....

 

I made an error, eyesight getting worse I guess. It's 1/2" by 18 threads per inch.



Standard fine thread bolts at the local hardware are 20 TPI.

 

Depending on how ambitious you are, and how nice of a job you want, you could remove the intake manifold. That would allow you to drill out the holes to 33/64" and tap 9/16"-18 threads in there. Then, buy some short 9/16"-18 bolts.

I use real a strong magnet, and stick it to the piece I'm drilling, to keep the chips from falling in, where you don't want them to go.

Or...you could always fill the holes with JB Weld, or Lab Metal, and sand the face of the filled hole smooth.

Rich

 

I made sure of the thread/pitch and depth, then did a search online and found some with a hex-key head that fit flush to the manifold, kind of like a set screw. They were a bit expensive since I had to order them. Unfortunately, I do not remember where I ordered them.

 

Although I could be wrong, it appears you need 1/4" NPT pipe plugs. For that diameter hole, the 18 tpi is a typical pipe thread pitch. Check with your local hardware store and buy brass pipe plugs. They will be much easier to remove as compaired to iron pipe plugs if you ever have to re-install the exhaust air injection system.

Ed

 

I had the same Issue when I used later v8 manifolds on my Gremlin. They had air injection tubes like yours had same size everything. I kept the bolts from my manifolds and bought thick steel spacers. They where 1/2" inner diameter, 1/2" thick and 1" outer diam.

Worked like a charm......

Essentially they just mimicked the banjo washers on the air tubes...

 

www.Fastenal.com will have what you need.

 

You could try to tap those holes to a new thread while the engine is running. Exhaust will blow most of the shavings out, and the rest will go harmlessly towards the muffler.

 

That is the route that I took. The thread per inch is the same but the plugs are tapered national pipe thread instead of of machine thread. The pitch is a little different on the threads as well. I was just trying not to damage the manifold and air tube system just in case there was some unfortunate soul looking for these parts in order to satisfy the kalifornia smog monster. You never know

Here's a link to the part: http://www.drillspot.com/products/350345/Parker_4_PHH-S_Hollow_Hex_Plug
I got them locally at McFadden Dale for $0.80 each.

I just put some of my favorite anti-sieze on there and cranked em in. Looks clean. Hope they don't leak, threads aren't a perfect match but I don't think I damaged them either.

 

When I had to put a new head on my 151 byears ago the only ones available were the ones with the smog/air pump fittings (off of a Fiero). At first I used 1/2 inch steel freeze plugs to plkug up the holes, but they ocassionally came out (very loud) so I later got some of the fittings in a junkyard, ground & drilled the tubing out and welded up the holes then threaded them right in,,never had another problem.

When I did my engine swap to the Ford 5.0, there was a large 5/8 or so) hole in the rear of each head, same purpose, just one inlet for the entire side of the engine, pipe plugs sealed them up great.