ARP STUD INSTALL BLOCK THREAD FAILURE

[PwrSmoke]

Bizarro World!

I have heard of this happening in cast iron but never seen it. I have done it on aluminum blocks by overtorqueing, sometimes by not paying attention, or a mis-adjusted torque wrench (several VW air cooled, a Jensen-Healy and a Rover V8) My first guess was torque wrench calibration too but if it's Ok, my next suspect is the tap or the tapping process having damaged the threads. Or corrosion in the threaded holes, weaking them after the bottoming tap was run thru. You may never know what the chicken is in this case but I'll bet you will be EXTRA careful the next go-round. I don't have any engine work to do in the near future but I'm gonna be extra careful too in case it's contagious! Good luck!

 

[typ4]

Well here is a tidbit FWIW, I torqued my studs to 110 100k miles ago and all has been well. 125 on a fine thread is pulling a llot of stress on the block. Fine threads provide much greater "leverage" on the fastener. Good luck with your repair, it sucks no matter why or how.

 

[IDIoit]

FWIW,
and i hope others chime in,
i would be researching the thickness of the blocks, and head bolt bosses, i think a redrill and retap to 9/16 would be stronger than a helicoil.
may as well do em all
bolts are bolts, and studs are studs.
im sure you can find something with the same tinsel strength.

 

[FORDF250HDXLT]

FWIW,
and i hope others chime in,
i would be researching the thickness of the blocks, and head bolt bosses, i think a redrill and retap to 9/16 would be stronger than a helicoil.
may as well do em all
bolts are bolts, and studs are studs.
im sure you can find something with the same tinsel strength.

yeah if that's possible it would be good,however you would need to have it done at the machine shop.that's not something to attempt at home.for the cost of the labor and then the hardware it's probably just cheaper to find another block.

 

[kcwright1979]

I was just following ARP's instructions and its a big lesson learned for sure.

 

[PwrSmoke]

Well here is a tidbit FWIW, I torqued my studs to 110 100k miles ago and all has been well. 125 on a fine thread is pulling a llot of stress on the block. Fine threads provide much greater "leverage" on the fastener. Good luck with your repair, it sucks no matter why or how.

So you think ARP's 125 lbs-ft is a bit high for the block? Considering the factory head bolt spec is 100 lbs-ft, you may be right. I wonder why ARP went so far above?

The 6.9L factory spec is 75 lbs-ft. and the ARP spec is only 80 lbs-ft., a 7% increase. A reasonable increase. A 7% increase to 100 lbs-ft is 107 lbs-ft, real near the 110 Typ4 used. 125 lbs-ft. is a whopping 20 percent higher. Something is very fishy here IMO and I wonder if they have thought this thru clearly. In a perfect world, with a perfect block, maybe 20 percent more is fine but with 30 year old trucks, perfection is hard to find.

Have we verified the instructions say 125 lbs-ft? That's step one, obviously. If so, I think it might be well worth the OP's time to point these things out to ARP. I've always found them to be a stand up outfit. Maybe they can review or revise their instructions. If they do, and find them in error, it wouldn't be inappropriate for them to make some kind of a peace offering.

 

[typ4]

My reasoning was that at 100 on a fine thread is a lot more pressure than 100 on a course thread bolt.
In Detroit Diesel manuals they have one torque spec for the head bolts and another for the Locating studs which have fine on one end, soooo, this is how I made my decision to go to 110 on my engine.
It has survived 15 lbs boost and over 240* too many times.

 

[OLDBULL8]

A 100 ft lbs is a 100 ft lbs, no matter if it's a course or fine thread, the tension is still on the course thread. Since the course end of the stud is already "seated", the fine threads will "seat" the washers and "form" the nut threads more accurate pertaining to fine threads.

The mechanical advantage of a screw thread depends on its lead, which is the linear distance the screw travels in one revolution.[2] In most applications, the lead of a screw thread is chosen so that friction is sufficient to prevent linear motion being converted to rotary, that is so the screw does not slip even when linear force is applied so long as no external rotational force is present. This characteristic is essential to the vast majority of its uses. The tightening of a fastener's screw thread is comparable to driving a wedge into a gap until it sticks fast through friction and slight plastic deformation.

 

[Agnem]

Fixed the title. We wouldn't want anybody doing a search to get too excited. Sorry about the bad luck. Let's put that down as a recommended torque to avoid.

 

[icanfixall]

Thanks for changing the thread title. It was misleading the way it was worded.

 

[Greg5OH]

FYI i went to 132 ft lbs on my ARP stud sin the 7.3 too much? maybe, but it feelt good and fine. Those heads aint never lifting. Might collapse a piston before that.

 

[FordGuy100]

If the OP found rust in the holes that stripped, we dont need to look further into the torque specs. That would be the reason why they stripped out...fatigued threads/base metal. As for helicoiling, did ARP tell you to do that, or was that something you were thinking? I have never heard of doing that to the block for headbolt/studs...hopefully it works.

Otherwise, its time to find yourself a short block.

 

[mblaney]

Here is a nice table of clamp force vs torque. I am sure the ARP studs are a higher grade than what's included on this table but what's more relevant is what you are trying to achieve. It's great to have a fastener that is grade "11" and think you can torque the crap out of it but in a properly designed assembly the fastener should be the fail point. Your stud clamping force only has to be something more than the expected 'lifting force' from compression. Drastically increasing assembly torque is not achieving anything. At 132 ft lbs the stud is most likely near its yield strength!

Just trying to be helpful... the OP thread most likely failed for one of two reasons:

1. the stud stretched which causes the top block (hole) thread to fail, then the next thread, and the next... until the whole thing comes out. It is unlikely that the ARB has much stretch to it (within the threaded portion).

2. The contact area was insufficient for the stress (shear) due to poorly fitted thread forms.


In this case I would check two things:

1. The ARB stud thread - verify the major diameter with a caliper. You probably can't measure the pitch diameter (need thread wires and a really good micrometer for that) but I would inspect the thread form to see that it appears to be ok.

2. Check your block (clean holes) with your original studs and the ARB's for fit. You ran a tap through them - was it the correct one? If the original stud (or the ARB) is loose fitting you have found your problem. Check the stripped threads; are there any left? Use your tap to check again to see if any part of the thread is left. If there are threads left then your tap was oversize, or the stud was undersize.

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[Greg5OH]

Blaney, justin from r&d testef stock 6.9 bolts, 7.3 bolts n 7.3 studs, if i remember correctly the stud yield was north of 150ft lbs

 

[Greg5OH]

Here is the thread link.
http://www.ford-trucks.com/forums/1306098-head-bolt-stud-tech-thread.html

1-2" arp head stud yield point was betwwen 180-190 ft lbs. crank er to 150 boys. Im at least 130 and it felt fine. I do think using the tap might have conpromised your threads OP. but you would have felt it cutting decently fir tjis to happen. Or.. Just a lemon block?
Sorry i digressed