Head studs trouble

[Scott H]

Myself and a couple club members are rebuilding a motor for my dads ‘62 convertible.
Last night while torquing the heads this happened. I didn’t make it to the 30ft lbs before it stretched and snapped off.
All of the Clark’s replacement studs have this line as shown in the second pic and that’s where it snapped. Anyone else have any issues with replacement studs?

[davemotohead]

I have never used them but funny it broke right at that line and looks to have stretched first? I would certainly let Clarks know about this and send them pictures! You don't want to be drag racing the guy in the VW next to you and stomp on the gas and have your head fly off!

[Phil Dally]

That has to be a defect.

[Dennis66]

Either a defective batch (with at least two), or maybe some kind of intentional shear point to protect the block? I just glad I didn't have any issues putting mine together.
I did have a '66 110 block that I junked and I was going to save some, or all of the studs, but they wouldn't budge and I even used a little heat on one. At that point I tossed the whole block. Dennis

[66vairguy]

Either a defective batch (with at least two), or maybe some kind of intentional shear point to protect the block? I just glad I didn't have any issues putting mine together.
I did have a '66 110 block that I junked and I was going to save some, or all of the studs, but they wouldn't budge and I even used a little heat on one. At that point I tossed the whole block. Dennis

Interesting about the Clark's studs. I have seen folks break off a factory stud trying to remove it, but they went WAY PAST 30ft lbs. when it broke.

I've repaired pulled stock studs and I can tell you those original studs are TOUGH. The stud threads that go into the block are NOT a unique pitch. The last three to four threads (screwing the stud into the block) have a shallow thread valley, peak dimension is the same as rest of threads. This shallow part of the 3-4 threads bind the stud into the aluminum.

When repairing a pulled stud with a Time Sert (they don't give) you have to recut the stud factory threads so the stud does not bind in the Time Sert before it is fully screwed in. WOW -- I ruined a basic die on those threads. I had to get a high quality die and had to use STP for a cutting lubricant AND IT WAS SLOW GOING. It worked, nice smooth threads.

[davemotohead]

I agree, the factory studs are hard as hard can be, when trying to chase the end to fit into a time cert takes a good quality die, good lube and patience. I did a entire Case once with time serts and the studs were the worst part!

[toms73novass]

That stud looks like a "dogbone" test sample that is used to test the tensile properties of materials.

There is NO WAY that at 30ftlbs they should be doing that. My bet is that Clarks has them sourced from overseas and the supplier substituted a substandard alloy.

[davemotohead]

Hey Scott, on my way to the ranch and will look for a NOS GM replacement for you, I believe I have .001 and .003 oversize. I am pretty sure I do and if so will toss one in the mail for you on Thursday

[Scott H]

Clark's saw my post and contacted me. They immediately sent a replacement stud and said they would test their current stock to make sure there wasn't any bad ones. This is the only one that broke on us and the rest have been fine.
Thanks Clark's for looking out.

[caraholic4life]

It is nice to know that Clark's takes the time to peruse the forums and see what is going on.

Taking positive action when they realized there may be an issue with one of their products is commendable and says a lot about them as a business.

[Brizo]

Scott H., I would be very afraid of all the those replacement studs you put in. As was said, the originals were very hard and they acted as "tensile springs" to expand an contract with the engine. That broken stud looks like its just common steel. Try clamping a Vise Grip on one of the new studs. If the stud is as hard as it should be, the teeth will leave no indentations.