marshal135

Hello everyone,
I purchased an original '69 828 RH exhaust manifold.
I has been painted or treated w/ unknown coating.
I'd like to clean out the threads in the air tube mounting holes before
installing plugs. I'd also like to clean the three threaded holes with a tap first in flange area where the heat riser and down pipe are attached.
Does any one know the thread pitch or tap size I need to use for the air hole threads and the flange hole threads?
Thanks in advance.
Marshal

jnb5101

flange bolts are 3/8 X16, i think the air holes are 1/4" npt.

marshal135

Jnb5101,
Thanks for the thread pitches.
You were spot on!
I ran a tap through all holes last night and all the threads were good.
Lucky I had the right size taps on hand.
A little rust caused some initial resistance.
I shot some kroil in there and went at it.
They cleaned up nicely.
You never know how these old manifolds were treated but this one held up well.
Marshal