Vintage Mustang Forums banner
1 - 18 of 18 Posts

·
Registered
Joined
·
956 Posts
Discussion Starter · #1 ·
Hi Friends

I have been searching for months on my garage queen for a bad lifter sound or exhaust leak. SHop vacs tests, soapy water sprays and finally the only thing that worked was a good old Oven MITT on a cold start engine. I was throttling header pipe surfaces with the mitt when ........

I can believe what i found, So help me understand !

I have a hole that was used to mount my Transmission tube. Its was plugged which never amounts teh tube flange because its too big for the tube flange hole. So I could never find the right adapter, So i got lazy and left this off ..It just a mounting point. right ! WRONG ! I cant get my eyes back there and when probing I find the large hole is pumping out air on a idling engine. WTF! these are not smog heads so why is this hole open?

I have been struggling with 10 MPG prb;ems, Ive changed carbs, just finished a valve lash adjust and ..........can this really cause 10 MPG..loss, The push is gentile garden hose strong but i can seal it with my finger no problem.

the smaller threaded hole below the freeze plug is burned but not pumping air.

What is this !
Automotive tire Motor vehicle Water Automotive lighting Orange

Motor vehicle Automotive tire Automotive design Automotive exterior Wood

Tire Automotive tire Wheel Automotive lighting Motor vehicle

Automotive tire Hood Automotive exterior Vehicle Automotive lighting

Black Gas Bumper Automotive tire Motor vehicle
 

·
I won a special award
Joined
·
8,784 Posts
You have heads that used thermactor air injection in their original configuration. Use plugs from Silver Seal # 6556. You'll need a quantity of 2.
Yup. The transmission dipstick tube does not mount to that. It goes on one of the transmission bellhousing bolts.

Automotive design Auto part Font Automotive wheel system Toy
 

·
Registered
1967 Mustang Convertible
Joined
·
1,244 Posts
  • Like
Reactions: LSG

·
Registered
Joined
·
956 Posts
Discussion Starter · #6 ·
You have heads that used thermactor air injection in their original configuration. Use plugs from Silver Seal # 6556. You'll need a quantity of 2.
Thanks Emberglo SOOOO much ! I am still a bit perplexed. I has a pressure coming out the hole .. why is that... Im fearing my heads are cracked?
 

·
Premium Member
Joined
·
1,066 Posts
Thanks Emberglo SOOOO much ! I am still a bit perplexed. I has a pressure coming out the hole .. why is that... Im fearing my heads are cracked?
Those are open to the exhaust ports on an emission control engine. Get those plugs and you will fix the issue.
 

·
Registered
Joined
·
956 Posts
Discussion Starter · #10 ·
Those are open to the exhaust ports on an emission control engine. Get those plugs and you will fix the issue.
Thanks Rusty ........okay So I thought I had 65 heads on my 66. The engine stamp on the block is '5'. So okay 66 heads on the engine. But they are not smog heads. I have a set of those with hole inputs each cylinder. Still confused.
 

·
Registered
Joined
·
956 Posts
Discussion Starter · #11 ·

·
Registered
Joined
·
593 Posts
Mr Angry
you also have holes below the freeze plugs . Are yours producing air Cuz I cant get back there to know. I dont feel air out of them. And wonder why mine are burned.
I connected the engine ground to the passenger side below the freeze plug. Nothing on the drivers side. I had no exhaust leaks.
 

·
Registered
Joined
·
40,959 Posts
Thanks Rusty ........okay So I thought I had 65 heads on my 66. The engine stamp on the block is '5'. So okay 66 heads on the engine. But they are not smog heads. I have a set of those with hole inputs each cylinder. Still confused.
There were 2 different styles of Thermactor used. The more common ones are "internal" with the holes on the ends of the heads. The "external" version used a "spider-like" manifold, like GM used on its engines with individual holes next to the exhaust ports. IIRC, the "internal" versions were cast at Windsor foundry and the "external" ones at Cleveland, or vice-versa. BOTH types are "smog" heads.
 

·
Registered
Joined
·
956 Posts
Discussion Starter · #14 ·
There were 2 different styles of Thermactor used. The more common ones are "internal" with the holes on the ends of the heads. The "external" version used a "spider-like" manifold, like GM used on its engines with individual holes next to the exhaust ports. IIRC, the "internal" versions were cast at Windsor foundry and the "external" ones at Cleveland, or vice-versa. BOTH types are "smog" heads.
Thanks Bart

I ve only known the External type .............So I guess the thermactor holes exit air into a tube for a smog system to re burn gases?
 

·
Registered
1965 289 Hype 4-speed coupe
Joined
·
16 Posts
I ve only known the External type .............So I guess the thermactor holes exit air into a tube for a smog system to re burn gases?
No, "re burning" would describe a later type of emission system, aka the EGR.
Thermactor was a short-lived (1966 - approx '69) pumped air injection system called an AIR (air injection reactor) that just provided extra air directly into the exhaust port downstream from the exhaust valve:

Automotive design Automotive exterior Bumper Bicycle part Automotive wheel system


:
 

·
Registered
Joined
·
7,323 Posts
No, "re burning" would describe a later type of emission system, aka the EGR.
Thermactor was a short-lived (1966 - approx '69) pumped air injection system called an AIR (air injection reactor) that just provided extra air directly into the exhaust port downstream from the exhaust valve:

View attachment 826881

:
That’s the External style head.
 

·
Registered
Joined
·
739 Posts
I used these to block the holes in the GT40 heads I had, wish I would have known about the ones Emberglo pointed out:
.
.
But looks like its a just 5/8-11in bolt. See if you can find a bolt and plug it up be alot cheaper.
Should be a standard pipe-thread hole.
Any local hardware store should have something U can thread in there, using some sealer compound.
Just don't drive some long threaded shaft in there and puncture something. Use something that is just deep enough to fill the hole depth.
 

·
Registered
Joined
·
40,959 Posts
Should be a standard pipe-thread hole.
Any local hardware store should have something U can thread in there, using some sealer compound.
Just don't drive some long threaded shaft in there and puncture something. Use something that is just deep enough to fill the hole depth.
No, the Thermactor holes on the ends of the heads are 5/8-11.
 
1 - 18 of 18 Posts
Top