The pipe flange is metric.

The head should be 3/8-NC, but it may have interference threads sometimes used in cast iron. Those are the ones where the root diameter is filled in to offer some resistance to loosening. I have not seen interference threads like that on the head - on the flange studs, yes.

 

Thanks for the reply.
Others have said both the head 3/8-16 & pipe flange 7/16-20(?).


I may see about picking up a metric tap & die set more so I have it when I need it but can check the threads before thy the SAE set.
Dave ----

 

I'll second this, that photo was worth 2.5 million words by my calculations.

 

Just to throw fuel on the fire, have seen studs recommended that are 3/8 x 20 coarse thread to go in the head, and 3/8 fine thread (think 3/8 x 28?) for the stud part that goes through the actual manifold tabs. Think that is what I have on order from Fastenal.

 

agreed. I have the same 2-ish inch studs with UNC thread pitch to go into the head, and UNF pitch to fasten the manifolds. Used quality crimp nuts, factory "donut" washers, and some custom hexagonal washers I cut out at work using a waterjet that go under the donuts. They get a good bite on the manifold mounting ears. Used them with the stock 1 bbl intake/ efi manifolds, edelbrock 1bbl (modded and ported for a mc 2150) / efi manifolds, and an offy C intake/ efi manifolds. making sure to get clean/shiny mating surfaces and swapping the gasket every time, torque values are consistent, and no leaks following proper torque sequence before/after initial heat cycle.

 

My search shows the proper torque value is 25'/# correct?

 

I have a ford truck shop manual that says 23-32 ft lbs. I suppose you may find a few different answers, depending on where you look, or who you ask. I'll torque the fasteners in the directed sequence in steps. I start at 15, torque everything, then 23, torque, all, and finally 30. Then I fire it up, let it run...let it get up to normal operating temp. Shut her down and take a long beer break. Once I'm sure its nice and cool, I come back and run thru all of them at 30 again, and then leave it be.
Every DIYer has their own preferences on specific torque values within the given ranges. This is not to say mine is best, or that their's it right or wrong. This has worked for me repeatedly...and since I'm a creature of habit, I stick with what works for my applications. There are plenty of folks out there that have a lot of success using different techniques though.

 

This is exactly what i needed. Thanks.

 

I found the 5/16 flat washers are too small for the 3/8 inch studs. I went to 3/8 washers.

 

ive got to order me one of those