Atomic A4 Head Studs question

[pastorscott]

I pulled my head, and need to reinstall, is there a reason why the atomic A4 head studs are smooth bore going through the head and only threaded on both ends? The replacement studs are quite costly at Moyer marine. Is there a reason not to use studs that are threaded all the way through? something like this Tacoma Screw Products | 3/8\x22 x 2-3/4\x22 Automotive Studs, Fine & Coarse, 10/PKG or like this 3/8 Coarse/Fine Studs

thanks

 

[Indysailor]

I wouldn't do it, but I'm not confident enough in my own experience to stray away from spec in such a critical area on the engine. Have you asked on the Moyer A4 forum? There are more than a few folks there who can answer this question, some of whom may be here.

 

[Indysailor]

Thinking about this a little more, I wonder if the stud design is so that they will stop turning at the proper depth in the block rather than bottoming out against the block? Plus, no threads at the seam between the block and head, perhaps less risk of leaking?

 

[fred1diver]

No thread between them will allow the head and block to compress the cylinders equally, if there is thread it will be hard if not impossible to have an even compression everywhere.
So yes less chance of leaking

 

[TimFromLI]

I haven no experience with Atomic engines but plenty of experience with removing and reinstalling heads on engines. It's been my experience that the seal is made by the head gasket. And it seals the block to he head preventing oil and water passages as well as cylinder pressure to leak. I can't see how anything but the torque and grade of the stud would matter in sealing the passages and cylinders. Unless the head stud bores are threaded- not likely. That said, I'd still get the opinion of someone who rebuilds engine like a machine shop.

 

[fred1diver]

The 2 times I rebuilt motorcycle engines, the head to block studs weren’t threaded all the way, only at the block

 

[kloudie1]

Since this is a cast iron head and cast iron block, the grade 8 studs from Tacoma will be fine. If we were talking aluminum head to a cast iron block or aluminum block, the oem stuff would probably need more study before substitution.

 

[jssailem]

Is there a reason not to use studs that are threaded all the way through?

I am not a mechanic by education. I have learned what I know about engines by doing it and asking a lot of questions.
I found this image of 4 cylinder block with studs exposed.

Thinking about your question, I was taken down the rabbit hole of stud fasteners and why they are used.
My first thoughts were about strength. The threaded portion of a stud has material removed, making the fastener's core diameter smaller. My thinking: The process of creating the threads reduces the strength of the stud.

Then I came across this discussion.

In terms of function, the use of studs provides much more accurate and consistent torque loading. When a bolt is installed, the act of tightening results in both twisting (torsional load) and stretching (vertical, or axial load). This results in the bolt being exposed to two forces at the same time, as well as experiencing frictional loads at the thread engagement. When the nut is tightened on a stud, the stud stretches on its vertical axis only. The exposed end (top) of the stud features “fine” threads, which allow more precise and therefore accurate, torque readings when the nut is torqued (or torque/angle tightened) to spec. by Mike Mavrigian​

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If the purpose of the fastener is to accurately locate the engine head and provide consistent torque loading of the head to the engine block, then a stud with a smooth middle would be the preferred choice.