The shrinking inch (rocker assemblies onto new STD heads)

[DuoDave]

Have inches gotten smaller over the last forty years? I've been transferring my original rocker assemblies onto my new STD heads. I had a hell of a job screwing the mounting studs into the heads. They were a really tight fit. I bought a new 5/16s UNC tap and tried it in the old heads. It ran in no problem. Tried it in the STD heads, okay there too. Tried screwing in the studs again. Still way too tight. I ended up cutting down the threaded portion of the stud so they had less far to go in and eventually persuaded them into place. Now I am faced with the same situation with the top motor mount studs. It seems like the original studs and the threaded holes in the original heads are a tiny fraction larger diameter than the STD heads and the tap I bought. Am I missing something or has anybody else encountered this? ???

[dirtydistrict]

Duo, I had exactly the same trouble with the rockers stud: hard like hell even with teflon grease, i've been using a pile of nuts to screw them. I found that it was easier using studs from my old heads...rather than new ones. The top motor mount didn't showed any trouble and were easy to fit.
The studs were from Colony if I remember.

[VintageTwin]

One thing i learned about the construction industry is: GO BACK TO THE ORIGINAL CONTRACTOR, if you have a problem. Call STD and get this info straight from God. He has his own chair in the tech dept. Direct at..at.. gotta go find the number.

[Cotten]

If you check out SAE standards, there are different thread clearances for different applications.
Since rocker studs (and cylinder studs, etc.) are expected to NOT be removed, they have extra tight 'aircraft' tolerances.
This makes them a b-i-zitch to r & r, but it is proper and correct.

PS: My inch has shrunk quite a bit since I reached 40!

[DuoDave]

Thanks for the info, Cotten. You've restored my faith in STD's build quality. Knowing it doesn't make screwing the studs in any easier, though.
Talking of screwing and studs, I'm sorry to hear about your shrinking inch, but I have it on good authority that it's not how big it is, but what you do with it. ;D

[Cotten]

Yeah, they all used to tell me that, even before it shrunk.

(Thank gawd I'm married now, and don't miss it.)

Back to mechanical 'studs',.. It is a real good question to ask just how these gn*t's-*ss-tight fasteners are actually supposed to be assembled.
I don't have a decent answer, as they often give me fits.
Anyone on this forum know how the automotive or aircraft industry does it?
Anyone have a forum where they can ask?
Thanks in advance!!!

[PanPal]

Have you tried heating up the bare head before screwing the stud in? Could also freeze the stud.
They make .005" over 5/16 taps, but how loose will the stud get when the head heats up? Could be this is why the fit is so tight.
Machinist handbook???

The machinery handbook states that thread standards were changed in 1949 and again in 1959. What year is your pan???
This still does not explain new heads and new bolts not fitting well.
I did read that they would get the male part to a sub zero temp before installing parts.
And this is how you fit a square peg into a round hole

[panoply]

DuoDave,

Did you ever get your studs transferred? If so what worked for you?

[DuoDave]

Like I said, I cut down the threaded portion that screws down into the head and eventually got them screwed down far enough so that they would not foul the pan covers. I was seriously concerned that if I had tried to screw them in the full length that I would damage the threads in the heads or even crack the alloy around the screw holes. I am back at sea now so I have not installed the top motor mount studs yet. I think I will try gently heating the alloy around the hole first. The expansion should help things along.

[57stroker]

Heat transfers quickly! You may consider coating things with anti-sieze. When things stop moving when they are warm, they are usually there for life! Find some good nuts and lock them together and use an inpact gun. If you know a machinist, they could make you a blind nut to use w/ the air gun. Good luck!

[kell]

I assume a blind nut means the hole doesn't go all the way through. Maybe you could just weld something onto one end of a nut to accomplish the same thing easier than using a drill and a bottoming tap. If you can do it without warping the nut an awful lot.
A "long nut" might be your best bet. Like a regular nut but a lot longer! Maybe even an inch!

[57Kicker]

Is there a possibility that the threads are galling? If so anti-seize would work as 57Stroker suggests.
Maybe this is too little-too late...just a thought

[DuoDave]

Sometimes I can be pretty dense. The solution to a problem can be so obvious that I can't see it. :
I already know that a UNC tap fits perfectly in the threaded holes in the STD heads, so if I run a UNC die up the threads of the top motor mount studs they should screw in no problem. How simple is that?

[Cotten]

I suggest a sturdy grade of Loctite, and use your rocker blocks to align them while it sets up.