Head plug?

[GaryOR]

Trying to get our newly purchased '78 Scout II with newly rebuilt 345 running. Have quickly learned that po doesn't stand for previous owner; it represents how angry I am with the idiot that attempted to rebuild (and gave up on) it before I bought it.

I discovered one more stupid mistake he made: forgot to put in the last "cylinder head plug" which accounts for the blowing sound we get when turning over the engine.

Problem is, I don't know exactly what it is (for my understanding) as well as to purchase another.

I'll attach a photo later if I can't get an answer from my description: each cylinder has one, forward of the plugs, tapped hole approximately 3/8 inch in diameter, plugged with a short square-headed (steel, not brass) plug. What are these?

 

[Robert Kenney]

No threaded plug other than the spark plugs should enter the combustion chamber.

I believe you are referring to a intake manifold plug. A picture will definitely help.

 

[Eric VanBuren]

It sounds like you are talking about the air injection ports. The are in the head in top of the exhaust port. The thread is standard tube nut 5/16" iirc.

 

[Dealbreaker74]

I'm not sure either. Forward of the plugs doesn't ring any bells. But there are air tubes (smog stuff) that normally penetrate the exhaust ports and allow the injection manifold to pump air into the spent exhaust for cleaner emissions. Often, people yard out all of the smog stuff and use pipe plugs in the heads where the smog tubes went. If one of those is missing, it will be very apparent when the engine finally starts. If that's what is is, you'll want to get one.

Throw up some pics when you can. There are a lot of folks here who have seen it all. And by the sound of it, you've got a few problems to uncock. Pics will really help out.

 

[Michael Mayben]

trying to get our newly purchased '78 Scout II with newly rebuilt 345 running. Have quickly learned that po doesn't stand for previous owner; it represents how angry I am with the idiot that attempted to rebuild (and gave up on) it before I bought it.

I discovered one more stupid mistake he made: forgot to put in the last "cylinder head plug" which accounts for the blowing sound we get when turning over the engine.

Problem is, I don't know exactly what it is (for my understanding) as well as to purchase another.

I'll attach a photo later if I can't get an answer from my description: each cylinder has one, forward of the plugs, tapped hole approximately 3/8 inch in diameter, plugged with a short square-headed (steel, not brass) plug. What are these?

Someone has removed the a.I.r. Runners (air injection system) and plugged the ports. Very common operation, I do that quite often. In fact I'm trying to get some time to do the same on my own rig today.

Those ports are normally sealed with the air injection tubes, those are a simple tube/flare fitting with a flare nut. We use 1/2"x20tpi cup point set screws for that, 1/2>5/8" in length. That is not an npt (pipe thread) thread form, but 1/2" 20 (fine) thread. A "square head" fastener indicates a pipe plug (1/8" npt) was used which is not correct and will not seal that port.

If the a.I.r. Port is not currently plugged, then all that results in is an exhaust leak at that point and does not affect engine operation at all other than "noise" and expelling exhaust gas where it's not supposed to be.

I install those plugs with anti-seize so that if I ever want to remove one (or all) I can do so easily.

 

[GaryOR]

That's the beast we're working on.



The steel plug is on the right with the hole on the left.

I think mm has identified what I am referring to. Assuming so, mm, do you know where I can find a full set of those plugs?

 

[Michael Mayben]

Any fastener company (fastenal, etc.) will have those, a very common shop item.

I buy 'em locally at eugene fastener, wilco farm store, jerry's (similar to home depot), home depot, lowe's, etc. Whoever has 'em in the bins, about $.85 each.

In this pic, you can see the four plugs in one of my 392 cylinder heads. Those have been in there about 11 years.

 

[Tiny Yokum]

someone has removed the a.I.r. Runners (air injection system) and plugged the ports. Very common operation, I do that quite often. In fact I'm trying to get some time to do the same on my own rig today.

Those ports are normally sealed with the air injection tubes, those are a simple tube/flare fitting with a flare nut. We use 1/2"x20tpi cup point set screws for that, 1/2>5/8" in length. That is not an npt (pipe thread) thread form, but 1/2" 20 (fine) thread. A "square head" fastener indicates a pipe plug (1/8" npt) was used which is not correct and will not seal that port.

If the a.I.r. Port is not currently plugged, then all that results in is an exhaust leak at that point and does not affect engine operation at all other than "noise" and expelling exhaust gas where it's not supposed to be.

I install those plugs with anti-seize so that if I ever want to remove one (or all) I can do so easily.

although I'm sure those will work, the proper part is an 3/8 inverted flare plug. Seals metal to metal against the flare face. Available at hillco fastener.com​

http://www.hillcofasteners.com/products/display_products_overviews.sd?iid=112&catid=&loc=show&headtitle=%20-%20inverted%20flare%20steel%20plugs%20chrome

 

[Michael Mayben]

The "engineered" plugs were available through navistar parts until a few years ago. In actuality, they were not engineered parts at all...simply "dog point" set screws!

Dog point means, a set screw with a projection on it about 1/4" long that serves as a "key" for a slotted shaft. That projection fit inside the air tube in the cylinder to reduce/eliminate a "whistling" sound made on some of the heads when the air tubes were removed. I've never encountered that issue and have never used dog point screws myself since they can be difficult to locate locally for me.

Some heads actually have tubing "insert" in the air port that is most likely rotted out and/or frozen in place. Some heads have the machined hole only with not tubular insert. No matter, all we are doing is simply plugging the hole to eliminate the exhaust gas leak.