Exhaust manifold stud size 1979

[temason]

I've read on this forum that the studs are 8mm x 1.25 pitch. When I looked at this size today at Ace Hardware, they didn't seem to match my parts. New nuts would bind after a few turns, same when I tried old nuts on new studs. My shop manual strangely does not mention thread pitch for manifold bolts- just 8mm, (yet specifies pitch for all other bolts!)
Is it possible these are 1.5 pitch?

[vandor]

The original studs are 8x1.25 for sure. I don't think there is 8x1.5 even made. I've seen 8x1.00, it's fine thread, but it's not common.
Maybe someone put the wrong parts in the bin at the hardware store?

[temason]

Thanks Casaba, that's a relief
Must just be corrosion/distortion on the old threads causing the binding. I was reluctant to use any more effort for fear of damaging what I have. I had found one post on the forum claiming 1.5 thread size but I will disregard.

I'm looking forward to buttoning the engine up this week!

[RRoller123]

Reviving this thread for my 80 FI:

Anyone know the answers to the questions below?

Want to verify this info, before I replicate what is probably a Franken-Fiat PO assembly....

The Exhaust Manifold stud threads are definitely #M8x1.25. And there are 5 of them. But I have a variety of overall length sizes installed in the existing head that is being pulled off, and I assume that by original design, they should all be the same. (?)

It appears that the stud intrusion INTO the head is ~16mm, consistent across all 5 studs.

BUT I have:

2 studs that measure ~54mm OAL, ~16mm un-threaded center section.

1 stud that measures ~51mm OAL, ~12mm unthreaded center section.

2 studs that measure ~42mm OAL, ~6mm unthreaded center section.

I am assuming that the correct INSERTION depth is ~16mm, yes?

The Exhaust Manifold casting seems about ~14mm thick, and the washers appear about ~2mm thick.

So we need slightly less than ~16mm as a center unthreaded section on the studs?

I also will assume that the overall length is not really that important and that the PO used what was available?

So, the 51mm OAL, 16mm insertion end, 12mm center unthreaded and 23mm nut side threaded section is the best way to go? (or as close as I can get to this)


Nothing is simple on these things when you go about undoing 37 years of "stuff" being done...

Comments welcome, as always!

Pete