Weird threads on a cylinder head

[Kidasters]

Found something weird this morning, just by chance.  I was messing with my box full of stuff for the cylinder head I am planning to put on my car.  I was just going to set the carbs on the head, so both were somewhat out of the way.  I figured I'd thread some of the intake studs into the head, and then just slide the intake onto the head, and it could sit there like that.

 

And the studs wouldn't thread into the head.  I checked the studs - and they are  M8-1.25, which is what they are on my stock head.  But, they won't thread up.  I'm wondering if for some reason, the threads on the head ar M8-1.0, which is weird.   The head is from an 83-320 I believe (casting mark 83), and it is ported for a mechanical fuel pump.

 

Any thoughts while I wait for my McMaster-Carr order of 25 M8-1.0 studs?  I checked both sides, and both Intake and Exhaust appear to have this issue.  Dang.

 

 

[Kidasters]

Never mind.  I was wrong.  The M8-1.25 thread in, but they are tight.  It's definitely not the fine thread though.

[ray_]

That 2 hours of research I'll never get back again!*

 

 

*well, 5 minutes on Realoem with was not conclusive...

[Kidasters]

Ha.  The Lies!

 

What am I going to do with the 25 M8-1.0 studs that show up from McMaster?  I should mail them to you.....

[jgerock]

That's the main issue ordering from McMaster Carr- they ship too quickly.

[Kidasters]

Ha.  Yeah, but it's not a problem.  Can't have too many fittings.  I just found a bag of 100 M8-1.0 nuts I didn't know I had!

 

 

[Simeon]

Studs are *supposed* to have a different thread form to the same thread bolt. 

[Kidasters]

Why?

[TobyB]

So they fit tighter into the casting...

 

t

[jimk]

14 hours ago, Simeon said:

Studs are *supposed* to have a different thread form to the same thread bolt. 

A different fit Class but not a different thread pitch which was the case here.