Exhaust leak from head plug?
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Mountain Pass
Joined: Apr 2003
Posts: 248
Likes: 2
Exhaust leak from head plug?
On my '78 F-150 (351M, 4-sp, 4WD), I have been looking for a bad exhaust leak for a while. Yesterday, I finally found it. In the front, top left (closest to exhaust manifold) corner of the passenger side head, behind the altenator, then is a small plug in a hole (the hole does not look to be threaded). It looks like a very small freeze plug, and it is original. The plug is about 1/2-in in diameter. In the middle of the plug, about a 1/8-in hole has burnt/rusted through, and exhaust is coming out here. What is the plug for? There is no water behind it. Has anyone experienced the same problem?
Elder User
Joined: Feb 2008
Posts: 999
Likes: 1
From: Davison, Mi.
The plug is for the emissions port that runs through the heads, front to rear, that intersect the exhaust port. Not sure on 351M/400s, but on 460's the two ports are connected in the rear of the engine with a cross tube.
You can just remove and replace the plug. But expect the other components in that system to rust out as well. The cross tube, the other plugs, etc.
You can just remove and replace the plug. But expect the other components in that system to rust out as well. The cross tube, the other plugs, etc.
New User
Joined: Jul 2006
Posts: 19
Likes: 0
I had the same problem when I bought my truck. I've got a 460 with the old dove-c heads. On mine there is a threaded hole next to the hole your talking about. for a quick fix I cut a piece of flat steel big enough to cover both holes. Then I drilled a hole for the threaded one, put some silicone on it and bolted it to the head. Worked well enough that I forgot about it untill now. I'm sure it could be tapped and just screw in a bolt to plug it.
Elder User
Joined: Feb 2008
Posts: 999
Likes: 1
From: Davison, Mi.
Yeah I had to do a similar fix on my 460. But since I almost never take the easy route, I duplicated the fittings at the end of the tube using CRS round stock and used those little yoke clamps that held the original tube on.
The plugs are still in there 5-6 years later.
The plugs are still in there 5-6 years later.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 787
From: Simi Valley, CA
376301S .. Plug, Cup Type 1/2" O.D. / Used to plug Thermactor holes in the heads.
Fits: 351C/351M/400
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380393S .. Plug, Cup Type 49/64" O.D. / Used to plug Thermactor holes in the heads.
Fits: 460.
Fits: 351C/351M/400
---------------------
380393S .. Plug, Cup Type 49/64" O.D. / Used to plug Thermactor holes in the heads.
Fits: 460.
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Mountain Pass
Joined: Apr 2003
Posts: 248
Likes: 2
Thanks for all of the replies. It was listed as the oil galley plug from CarQuest. I put it in and changed the belts, but the bottom hole on the altenator is stripped. When I get it all back together today, I'll start it and see if the other head has the same problem. I hope not, because the plug faces the firewall.
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