Intake Stud Failure Question

[Mark P.]

I installed this new intake manifold stud in my 1965 327 and tried to torque it to 30 lbs. The shop manual has 25-35lbs as the spec for intake manifold bolts.

The torque wrench was starting to have resistance then it let go. I backed it out and found cracks on both sides. I was lucky I stopped or it would have been a pain to remove.

I used an almost new snap-on 3/8 torque wrench that I recently checked against my other torque wrench and found them consistent.

I had ARP thread sealer on this stud like all the intake bolts. All the bolts torqued up uneventfully. I have installed my original stud and it torqued to 30 without issue.

Anyone else have this kind of issue with repro bolts or any advice on what I may have done wrong ?

[Jack H.]

Re: Intake Stud Failure Question

I doubt you did anything wrong. The way that stud fails looks pretty catastrophic and I would guess due to crappy material, bad porosity, etc...basically defective IMHO. I'd try to source another stud.

[Joe L.]

Re: Intake Stud Failure Question

I doubt you did anything wrong. The way that stud fails looks pretty catastrophic and I would guess due to crappy material, bad porosity, etc...basically defective IMHO. I'd try to source another stud.

Jack and Mark------


Absolutely yes. This is my greatest fear with "reproduction" fasteners. Effort is made to make them APPEAR original but is that "only skin deep"? I would NEVER use a reproduction fastener for a critical application.

[Mark P.]

Re: Intake Stud Failure Question

Thanks Joe and Jack. This rattled me. I just decided to order Spicer U bolts to hold my driveshaft rather than go with reproductions that I know nothing about. I have never had an issue with brands like GM, Moog, Spicer, ARP, Federal Mogul, Raybestos, Delco or Sealed Power stuff.

[Dan D.]

Re: Intake Stud Failure Question

Mark, your photo shows the stud to be Zinc plated. So the failure could be from Hydrogen enbrittlement if the stud was not heat treated after plating. That is the exact type of failure you get from Hydrogen enbrittlement, and unfortunately is quite common with Asian manufactured parts. I have been victimized by this before.

-Dan-

[Mark P.]

Re: Intake Stud Failure Question

Dan, that makes a lot of sense. It has very nice plating and didn't act like steel when I torqued it up. More aluminum like qualities.

Mark

[Gary B.]

Re: Intake Stud Failure Question

Mark,

If that stud is from LIC, like the paper under the stud in your photo suggests, then I seriously doubt that it can be blamed on a lack of understanding of or the lack of a process to deal with hydrogen embrittlement on the part of LIC or its suppliers. Companies like LIC that sell repro zinc plated bolts must have a manufacturing spec that addresses that issue for zinc plated bolts and studs. I suspect it is just a case of an uncommon failure that is bound to happen to some small percentage of fasteners. Some things just have defects.

Gary

[Mark P.]

Re: Intake Stud Failure Question

Hi Gary - it is from LIC. I sent the photo and a description of what happened. I think I'll reach out to a buddy of mine who has been a metallurgic engineer for Boeing for 30 years. Thanks,

Mark

[Richard G.]

Re: Intake Stud Failure Question

A metallurgic engineer is exactly where it should go for analysis. Anything less is speculation.
Engineering may have access to some cool new tools that can analyze the steel content using Xrays and only takes seconds to do.
One needs to know the composition before anything else. Composition will determine other factors like heat treating or hardness.
A couple of things I noted;
1) The thread root is very flat. Not the type of machining I ordinarily see.
2) The major diameter seems to be undersized from elongation. Likely the bolt has been over-torqued not over-tightened because of the poor bolt design. Not that you used an incorrect value, it was just too high a torque for this bolt design. Without more information it is impossible to identify the exact cause.

However, I am willing speculate that the material and heat treatment is likely substandard for the application.
The fact the other bolts survived is evidence of this.
All used the exact same lubrication and torque application. I would be surprised if anything but the size was specified by the vendor. They sell Corvette parts and are not an engineering firm. Sure they should have a specification. If they did it was ignored by the supplier. I have seen counterfeit A325 bolts that broke when torqued. They were used in assembling a overhead crane. This a critical application that only domestic bolts were specified. The vendor supplied what turned out to be fasteners from China. It happens.

Possibly they steel is 12L14 designed for easy machining and isn't even a hardenable alloy? Would be interested in the results of any testing or root cause analysis.

I have over torqued intake bolts in the past to mitigate a leak. Way over torqued, to like stupid values, and never broken a GM intake bolt.
Best of luck
Rick

[Mark P.]

[Richard G.]

Re: Intake Stud Failure Question

Hope my post wasn't confusing. GM designed the fastener in this position to be torqued to the same torque as all the rest of the intake bolts. Just like you properly did. The replacement fastener, you purchased, may not have been designed for this torque, which would have been a mistake by the vendor. However, knowing how many companies work, my guess it it didn't have a design/specification at all. The thought may have been; it's not critical so why spend the money for a proper design. Would have been better to guess at the specifications than just take the lowest bid.
Rick

[Kim C.]

Re: Intake Stud Failure Question

mark - et al, we are looking into this matter. I have no info yet. LIC

[Gary B.]

Re: Intake Stud Failure Question

Kim,

Can you tell us if LIC's manufacturing requirement for its zinc-plated nuts, bolts, studs, etc., includes a post-plating treatment to address hydrogen embrittlement?

Gary

[Kim C.]

Re: Intake Stud Failure Question

Kim,

Can you tell us if LIC's manufacturing requirement for its zinc-plated nuts, bolts, studs, etc., includes a post-plating treatment to address hydrogen embrittlement?

Gary

Gary , I don't have that information.

[Gary B.]

Re: Intake Stud Failure Question

Kim,

Thanks for taking the time to answer. If you find out, please let us know.

Gary