Engine/Transmission (1994 - 1998) Stupid Studs...

[wildmanben]

So Josh and I are putting his head back on after the long wait of finding a new head and having it o-ringed. Anyways, tapped the holes, blew the crap out, prepped the surface, got the head on and torqued the ARP 12mm studs. 25, 45, 90, 125. And for the bad now. 6 studs pulled out of the block at about 110-115ft/lbs. We used a moly lube on the threads and washers. Nice steady pull then crack and its downhill from there. What the heck.



So what do we do? Pull the head and get another gasket obviously. Do we drill the holes out and helicoil them? Will that hold? Or do we drill and tap all the holes for 14mm studs? Who's to say that if we repair the bad ones that more may do it at a later time during a re-torque?



When we pulled the studs out originally, they were all rusty and the holes were full or crap and oil and such. Cummins did a great job the first time on this. Not... Would the rust weaken the threads that much? I just dont get it. Where did we go wrong? Did everything by the book. Did the same thing to my truck and its holding up just fine. What gives?

 

[Skydiver]

If this happened to me I would prove the findings to the manufacturer and go from there.

Did I understand correctly you stated the head was "Brand New".

If it was used it may have been previously stripped out.

It won't help much but you might want to use a micrometer to check the bolt size against the tap.

I know this is very tough to handle after spending so much money and time .
Good luck!

 

[pwerwagn]

It stripped the threads in the block, not the new head.

 

[MAleksandrowicz]

I would go to 14mm. Like you said if you fix the ones that stripped, what's to say that others won't strip out. I wouldn't heli coil them. Do it once and do it right.

 

[Reb.B]

This is why i never tap the holes before putting in studs, you are only removing more holding metal. Need to go 14 MM or find another block.

 

[Bandit1]

to insure straight holes for the 14's the block has got to come out and be drilled and retapped and the head reamed for the big studs. i have heard from a very good machine shop that do to the nature of the force from the studs a helicoil will work just fine, but i would call another machine shop just to make sure.

 

[WDixon27]

i've never really liked tapping good threads espcially if it's in a critical area, if you could find a chaser that long that would be one thing, i modified the studs i installed to fit my truck instead of the truck to fit the studs, with the usual exception of grinding the valve covers

This is why i never tap the holes before putting in studs, you are only removing more holding metal. Need to go 14 MM or find another block.

 

[Joseph Donnelly]

Re-tapping is OK if all you did was chase the holes, not really cut out more metal. Any time you pull the head, coolant will flow into a lot of the head bolt holes, and some will be filled with oil because of the proximity of such passages and the use of the long head bolt passages in the head to carry oil to the rockers. You do need to clean out the holes, using about 100 Q-tips—preferable to compressed air as that would send the stuff everywhere. If you used moly lube, I suspect that you overtorqued the nuts on the studs to the point that they pulled the threads out of the block, and probably overstressed the threads in the other holes. Torque specs vary widely with the type of thread lubricant, as you are not only stretching the stud or bolt, you are experiencing resistance to turning from friction of the threads and the shoulder under the head. This friction is greatly reduced when you use moly lube instead of engine oil. A bolt that would be tightened to 70-80 ft lb with engine oil as the lubricant may achieve its design clamp load with 50 ft lb with moly lube. 120 ft lb is fine with engine oil and stock bolts. 120 ft lb with moly might be OK with 14 mm studs because of the greater bearing surface of the larger diameter threads in the block—I don't know. It could also be that the threads in the holes that failed were damaged previously, but that would be a rare situation.

 

[wildmanben]

OK, moly lube may have not been the right term. This is what we used and have used in the past with no troubles ever. So why would it matter now.



http://www.permatex.com/products/automotive/b_lubricants/specialty_lubricants/Permatex_Ultra_Slick_Engine_Assembly_Lube.htm



And yes the torque wrench is accurate to those who will blame that.