Engine noise issue

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Jayro

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73 mustang baby blue with clevo 351
Hey all, posted a few weeks back about a noise from my engine when i get over 50mph. Had it checked over as I couldn’t pin point the issue. So while the exhaust was getting done today they checked out the manifolds for me as I thought it was the exhaust leak causing noise.

They went over it and said exhaust manifolds not leaking BUT there is a small welsh plug (type plug) at the back of the head
facing the firewall. It’s maybe 1/2” diameter and set inserted into the head maybe 1/2” as well. They are saying it’s leaking out from cylinder out through this plug.

I’ve got no idea what it is? Any ideas or suggestions please 🙏

Thanks all.

On a seperate note, very happy with new exhaust and loving the tail pipes we opted for 👍
 

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Wisconsin
My Car
1972 Mustang convertible, 351C 2V with FMX (#'s matching)
Currently equipped with 351C 4V 4BM, .060 over, roller cam, Sanderson block huggers, -AC
Hey all, posted a few weeks back about a noise from my engine when i get over 50mph. Had it checked over as I couldn’t pin point the issue. So while the exhaust was getting done today they checked out the manifolds for me as I thought it was the exhaust leak causing noise.

They went over it and said exhaust manifolds not leaking BUT there is a small welsh plug (type plug) at the back of the head
facing the firewall. It’s maybe 1/2” diameter and set inserted into the head maybe 1/2” as well. They are saying it’s leaking out from cylinder out through this plug.

I’ve got no idea what it is? Any ideas or suggestions please 🙏

Thanks all.

On a seperate note, very happy with new exhaust and loving the tail pipes we opted for 👍
I like the turn downs! (of course) 👌🏻
 

Hemikiller

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65 coupe
You may have later model heads with the air injection ports. These had a manifold that bolted to the back of the head, which connected to an air pump. The PO probably used cup or welch plugs to seal the holes. This doesn't seal them completely as they holes are threaded. You can knock the plugs out and use a 5/8 thread bolt or socket set screw. You could also buy the special plugs that are offered by many supply houses.

Video below explains it pretty well.

 

Jayro

Well-known member
Joined
Mar 30, 2022
Messages
98
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My Car
73 mustang baby blue with clevo 351
You may have later model heads with the air injection ports. These had a manifold that bolted to the back of the head, which connected to an air pump. The PO probably used cup or welch plugs to seal the holes. This doesn't seal them completely as they holes are threaded. You can knock the plugs out and use a 5/8 thread bolt or socket set screw. You could also buy the special plugs that are offered by many supply houses.

Video below explains it pretty well.


ah that’s it. Thanks for that. Not going to be fun sorting it while the engine is in. Will play around today and see what I can sort 👍
 

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