Head Studs Breaking on L134

[Misdemeanor]

I ordered some new head studs about 2 years ago and when I started assembling the other day I broke some of the studs at 70ft lbs. Since I couldn't remember who I order them from I reorder from 2 different vendors since one had the long studs in stock and the other the regular or short studs. I have the same issue. They stretch or break. I am either doing something wrong or there a lot of other out there having the same issues. I have to assume the suppliers are all using the same manufacture and are all getting the defective parts. Does anyone know if NOS is available?

The center one is new unused. The left shows the stretch and the right shows it broke. This is the long stud



This is the short stud. Center is new unused and the right is stretched at 50ft lbs. the right has a nut welded on so I could remove

 

[NDT]

Buy some NOS parts from a reputable vendor. I suggest Mullins Jeep Parts. ArmyJeepGuy on ebay.

 

[just me]

70? That seems high to me. I just took a used set up to 60 without issue, but that is as far as I would want to go.
If you are damaging them at 50, I would first check that your torque wrench is calibrated.

 

[cwc]

Looks like a lubricant paste on the threads, what are you using?


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[Misdemeanor]

I put liquid teflon thread sealer on the block side and anti seize on the nut side. The studs are like butter. I can feel them start to stretch at 50lbs. The TM9-1804a in section 90 - "Tighten the cylinder-head bolds with a torque wrench from 65-75lbs...." It does say bolts not nuts. I see that some online say nuts to 60-65. There is no way I could go past 50 anyway. I think these are Crown studs. I wonder if the Omix-ADA are better. I'm trying to locate some NOS and have contacted Mullins. They have always sent me good stuff.

I have read that the threads should be dry and clean. I doubt the anti seize has anything to do with my problem but I think I will use the thread sealant on the next set and skip the anti seize for the nuts.

I will follow up as this progresses and try to determine who manufactures the studs since I believe this is my second set of defective parts.

 

[SCSG-G4]

I put liquid teflon thread sealer on the block side and anti seize on the nut side.

I have read that the threads should be dry and clean. I doubt the anti seize has anything to do with my problem but I think I will use the thread sealant on the next set and skip the anti seize for the nuts.

Sorry, the anti-seize is your problem! The actual torque at the threads is 15-50 percent higher than a dry reading. Pick up a copy of the Pocket Ref - ISBN 978-1-885071-62-0, go to the Fasteners section (about page 213), and check out the section 5 - Effect of Anti-Sieze Compounds, Lubricants, Platings, Coatings, Torque Coefficients, and Stress Levels on Torque for Carbon Steel Bolts. Read and weep!

 

[cwc]

Misdemeanor, you are fortunate that you did not pull the threads out of the block. I looked around on the internet a bit, and found a case where someone did that to one of these engines by using anti-seize on the nuts. If you don't have the pocket guide mentioned by SCSG-G4 handy, there lots of info on the internet about lubricants and their effect on the conversion of torque to bolt load (see "nut factor"). Search "anti-seize and over torquing bolts" for one person's experience with this issue.

You might want to take a close look at your block, focusing on the head bolt holes, looking for cracks or the head surface being pulled up somewhat. Some older engines do not have much of a counterbore in the threads...a counterbore helps prevent these effects by locating the "pull" of the fastener below the surface.

It is still possible that you got some bad studs, however. The fact that they broke rather than stripping the nuts suggests that could be the case. Normally nuts are supplied slightly softer than the matching studs/bolts, and if the fastener is overtightened the nut deforms; the "nut factor" increases dramatically, limiting the force developed in the fastener. Do you happen to know what the thread size/pitch is? Same both ends?

 

[cwc]

looking for cracks or the head surface being pulled up somewhat.

Sorry, I meant the block surface, not head surface...