Head Bolt Size Question

[lucky7_1080]

Long time listener, first time caller.

I’ve been working to troubleshoot what I believed was an exhaust manifold leak on the passenger side of my ‘79 for the last couple months. Just wrapped up install of a new manifold with remflex gasket. Fired it up, still audible leaking at the front of the engine. Before the engine warmed up I quickly started poking around to see if I could “cover up” where the leak was coming from.

Turns out there’s a bolt hole or vacuum connection at the very front of the head (see picture). When I stuck my finger in, leaking exhaust sound immediately went away.

Does anyone know if this is an OEM mount point for the alternator, a vacuum connection, or some other smog connection? Ultimately, I just need to know the bolt size so that I can plug it up. Any thoughts?

Thanks all!

 

[miesk5]

Yo lucky7_1080,
Welcome to our site!
Sorry, can't see well enough now due to macular degeneration of my "good" eye. However, other 79 owners can help.

Here's the 1979 Bronco/F Series Electrical & Vacuum Troubleshooting Manual by Ford via member Ziggy⚠ @
1979 Ford Bronco Wiring Manual pictures, videos, and sounds | SuperMotors.net
It shows Electrical component location, operation, troubleshooting, with wiring and vacuum diagrams.
It may be slow to download if you're finding that one website from which you download files operates slower than another, it's likely either because the web server is slower, or another device along the transmission route in the chain linking you to the web server operates slower.

1979 Ford Bronco Wiring Schematics, Connector Pin-outs, etc by Ranger429 @ 79 wiring schematics

1979 Bronco Brochure @ https://www.xr793.com/wp-content/uploads/2020/07/1979-Ford-Bronco.pdf via Dezo's Garage

1979 Ford Bronco vs. Blazer Article by Ford via Indybronco @ 1978 Ford Bronco Bronco vs. Blazer (79) pictures, videos, and sounds | SuperMotors.net

Ford Shop Manual Diagrams: 1978-1979 Full Size Shop Manuals, partial @ Technical Diagrams Archives
My Tablet takes hours to download, so try the first in this list as long as you have Adobe Acrobat 9 or later installed.
Includes:
Wiring Manuals & Diagrams Download PDF
This complete manual for the 1972-1979 Ford Bronco Includes Rear Lights Diagram
Motor Manuals & Diagrams Download PDF
This complete manual for the 1972-1979 Ford Bronco Includes Air Cleaner Diagram
Chassis Manuals & Diagrams Download PDF
This complete manual for the 1972-1979 Ford Bronco Includes '78 Brakes Diagram, Gas Tank Setup Diagram
Body Manuals & Diagrams Download PDF This complete manual for the 1972-1979 Ford Bronco Includes; Upper Body Diagram, Front Clip Diagram, heater Ducts Diagram, Tailgate Diagram, Console Diagram, Front Clip Diagram, Grill Setup Diagram, Heater Controls Diagram, Interior Trip Diagram, Rear Sheetmetal Diagram, Tiltwheel Diagram, Tire Rack
Let me know if the downloads are worth the effort.

Partial Chilton Manual for 1978, 1979, 1980, 1981 Bronco. Scanned by broncocity.com @ Bronco City
K
See Bubba's M-Block Ford V8 Workshop by Dave Reschm

See my mostly recovered View attachment 202203
site by schwim @ Ford Bronco And F-150 Links - FORD BRONCO
Enjoy our site!
Al

 

[L\Bronco]

Hey Lucky 7, That hole is where the air injection crossover pipe bolts, (It bolts to the back, but both heads are the same casting so the holes are on both ends.) There is an insert threaded into the holes that is capped internally (it's a blind hole), directly behind it is a rifle drilled passage through the head that is connected to each exhaust port.
The insert is either missing or has corroded out and is leaking. If there are still viable threads in there you can simply thread a short bolt in the hole to plug the exh leak.
The threaded inserts are very difficult to remove, especially when corrosion is involved.
Hope that helps
Cheers

 

[Tiha]

The threaded inserts are very difficult to remove, especially when corrosion is involved.

Oh that would **** if something is broken off in there.

I suppose you could drill it and drive a freeze plug in there.

 

[L\Bronco]

Oh that would **** if something is broken off in there.

I suppose you could drill it and drive a freeze plug in there.

The insert should be 7\16"NC threads in the ID, (I'm not sure what the OD threads are)
Should be able to thread a short bolt in and plug the leak easily, If it corroded through, the threads should still be ok.
Hopefully
Cheers

 

[lucky7_1080]

Thanks @L\Bronco. I’ll give the 7/16-14 bolt a shot first. I pulled the bolt off of the driver side, mounting the AC pump and steering pump to the head, but was too long to insert even with the alternator slid down and out of the way.

Assuming the insert ID threads are corroded, is there another easy / safe method for plugging? Not familiar with a “freeze plug” as @Tiha suggested.

 

[L\Bronco]

Thanks @L\Bronco. I’ll give the 7/16-14 bolt a shot first. I pulled the bolt off of the driver side, mounting the AC pump and steering pump to the head, but was too long to insert even with the alternator slid down and out of the way.

Assuming the insert ID threads are corroded, is there another easy / safe method for plugging? Not familiar with a “freeze plug” as @Tiha suggested.

He is referring to a pound in soft iron plug like the frost\core plugs you find in the block and the ends of cyl heads sometimes.
There won't be any significant pressure there, so if you have even marginal threads, a short bolt with some high temp rtv (silicone) should do the trick.
Let it cure overnight to be sure.
As long as the bolt will hold itself in, you should be ok.
It's just exhaust behind there.
Cheers

 

[L\Bronco]

Thanks @L\Bronco. I’ll give the 7/16-14 bolt a shot first. I pulled the bolt off of the driver side, mounting the AC pump and steering pump to the head, but was too long to insert even with the alternator slid down and out of the way.

Assuming the insert ID threads are corroded, is there another easy / safe method for plugging? Not familiar with a “freeze plug” as @Tiha suggested.

worst case, if its too corroded, try a s c r e w extractor, (easy out) with a ton of penetrating fluid (deep creep is my choice), you might get lucky. They are still available
Cheers

 

[Tiha]

If you can get anything threaded in there it would be better than a freeze plug. So drilling and tapping would be great if you have to and have the ability.

I was just thinking of other possibilities.

Places like napa, or grainer online you can get Freeze plugs in most diameters and they would work, but installing them can be a treat and if it leaks you start over.

I have not worked on what you are attempting so I don't have good advice there.

 

[L\Bronco]

If you can get anything threaded in there it would be better than a freeze plug. So drilling and tapping would be great if you have to and have the ability.

I was just thinking of other possibilities.

Places like napa, or grainer online you can get Freeze plugs in most diameters and they would work, but installing them can be a treat and if it leaks you start over.

I have not worked on what you are attempting so I don't have good advice there.

I have never attempted to remove one, however I have installed several when removing the air injection systems. (less rules up here)
Gives a cleaner look than a bolt.
But sorry, never tried removing one, I feel that it would be a bit of a challenge.
Cheers

 

[lucky7_1080]

Thanks all. So as it turns out, there was a small freeze plug in this hole. Unclear whether it was threaded prior and freeze plug added post-factory or not. There was a 1/16" hole in the plug letting exhaust out. I filled it flush with JB and it took care of the issue!