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Old 03-28-2015, 12:08 AM   #13
Titomars
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Join Date: Feb 2015
Location: Santa Rosa, Ca.
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Re: air injection manifold plugs

Quote:
Originally Posted by Pampas56 View Post
When I had to replace the air injection tubes on my 350, we drilled the old flare nuts out and cleaned the threads up with a pipe tap. We discovered that they were a standard 1/4 inch NPS thread and dug up a straight plug tap to do the job.

A 1/2 by 20 plug would work worse than a 1/2 by 13 plug as the normal pitch of a 1/4. inch pipe thread is 14 TPI
Ahhh but 5/16 inverted flare nut threads are 1/2 X 20. Anyway that's what I do on my pre 81 vehicles. Now I can't really speak for newer engines. They might be metric for all I know.
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1977 Chevrolet C/10 Silverado. Step-Side, Factory 454, TH400, 3.73 Posi 12 Bolt.
1975 Chevrolet El Camino. 350, TH400, 3.08 Posi 10 Bolt.
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