: Nice job on headbolt quality control



BIGGUN
06-15-04, 12:06 AM
Went to bolt up the heads on the 96 following 22/60/60/60 in sequence.
Noticed 2 bolts would spin EASILY in the 2nd round of 60 degrees. I got concerned and used the torque wrench set at 80 ft/lbs to do the last 60 degree tightening just to get an idea of what was going on. On the bolts that seemed normal the wrench clicked about 10-20 degrees into the last 60 degree tightening, I proceeded to go to 60 degrees. On the two that were suspect, and one other, the wrench NEVER clicked. I turned it down and checked those three, turning the wrench up a little each time it clicked without moving the bolt. The bolts would move at 65-68 ft/lbs. I thought the Timeserts were pulling out. That's all it could be right??? WRONG!!!

I removed one of the troubled ones, and one good one and switched them. The good one went in exactly as it should have and the wrench clicked at 80 ft/lbs right around 20 degrees into the last 60 degree turn. The suspect bolt, even fully tightened to spec still wouldn't set the torque wrench off set at 65 lbs............What kind of BULL&#!^ is that........ WHAT THE F*@% GM!!!

The second head was even worse only two bolts were good. AAAAHHHHHHHH!!!!!!!! Took the old bolts and cleaned them up, reloctited and sealed them, and used them in place of the new bolts. every one of them set the torque wrench off at between 15-30 degrees through the final 60 degree turn.

I feel like taking a sling-shot and returning them to the dealership through the showroom window!!

What the H@!! would you do?


Thanks for listening to my rant,
Kevin

zonie77
06-15-04, 11:06 AM
I would be concerned about getting more bolts from that batch! Let's see if Bbob knows anything about this. It sounds like bad bolts!

BIGGUN
06-15-04, 12:01 PM
Makes me wonder if knuckledragger's time-sert's were pulling out or not.
That's exactly what it felt like was happening here..........I don't know what made me think to try different bolts. I was ready to order the big-sert kit and do it again. That would have REALLY been annoying as I would have used the same bolts and had the same problem.

Have a good one,
Kevin

zonie77
06-16-04, 12:08 AM
One of the Caddy parts guys indicated there were some bad bolts back around 2000. I don't know if there is any truth to that.

Geno Castellano
06-16-04, 11:49 AM
There is usually some drag from the locktite patch that is applied to the head bolt threads. Possibly that is what is confusing the issue.

I am not aware of any "bad headbolts" anywhere. Given the number of head bolts installed daily at the plant I would suspect that they would have showed up there. "Bad" head bolts is a new one one me. Not sayind that it couldn't possibly happen. I have just never seen one, honestly.

BIGGUN
06-16-04, 03:07 PM
Geno, would that mean that the initial ft/lbs reading would have been off and I wouldn't have had the bolts in properly if I stopped at the last 60 degree turn?

Kevin

Geno Castellano
06-17-04, 02:07 PM
Geno, would that mean that the initial ft/lbs reading would have been off and I wouldn't have had the bolts in properly if I stopped at the last 60 degree turn?

Kevin


I think the answer is yes if I understand the situation correctly.

The basic premise of a torque angle installation is to take the joint to zero clearance with the initial torque and then to turn the bolt a specific number of degrees of angle to stretch it correctly. The angle is based on the bolt design, metallurgy and, specifically, the thread pitch. For example, if the thread pitch is 2 mm per revolution and the desired stretch to reacht the correct tension is 1 mm then the bolt would need to be turned 180 degrees. Same idea exactly that has been applied to rod bolts over the years. Most rod bolts require a bolt length measurement before tightening begins and then the spec is to tighten the bolt to a specific stretch not a torque. Just, in the case of head bolts and other blind holes, you cannot measure the bolt lenght with conventional means, so the stretch desired is expressed in the way of degrees of angle to turn the bolt ONCE IT IS AT ZERO CLEARANCE and the jount has no more freeplay in it.

So, a torque is initially specified that will seat the bolt and the joint and draw all the free play out of it. I always run the bolt down with a speed handle or something until I KNOW that it takes up all the slack and the torque required to turn it further starts to go way up. This is the "feel" when the joint gets "hard" as teh bolt is run down. Back off slightly and then torque to the initial torque and then procede to the angle specs for tensioning.

If the bolt is only run down looking at pure torque and the bolt binds a little on debris in the threads or excess loctite on the bolt threads or something (???) then you stop there the bolt will not be at the "zero clearance" point when you start turning it so it will not be stretched adequately and will not hold tension correctly.

I wouldn't say that this has been a severe problem at all since most mechanics know what is going on here and if they don't feel resistence on the "angle" steps they go back and run the bolt all the way down again and reset to the initial torque spec and start over.

From what I hear, in the assembly plant the head bolts are run down fully to a higher torque value, tensioned to a high angle, then backed off completely, retorqued to the specified torque and then "angled" to the correct angle for assembly to yield the correct bolt tension. This effectlively removes any excess locktite from the threads and pre-conditions the threads in the block for the final tightening steps. This preconditioning is necessary to make sure that there are no burrs or anything in the threads and it actually moves or slightly forges the threads in the block for extra strength. If there is any give to the threads in the block it is taken out with the preconditioning step before the final torque-angle spec is achieved.

If I do a head bolt or a Timesert repair I always pull the bolt down fairly hard to make positively sure it is engaging correctly and that the joint is pulling down to zero clearance, then back off, retorque to the initial torque spec and then go to the correct angle.

Geno Castellano
06-17-04, 02:10 PM
The blue patch that is on the threads of the head bolts is a micro-encapsulated loctite material that acts as a lubricant during pulldown and then a thread locking agent after installation. It is critical to the joint working correctly and must be there...that is the main reason that new headbolts are specifiec. The microencapsulated loctite might be dried out more on headbolts in service stock - especially since they might have been sitting in a warehouse or on the dealer shelves for years - so the prevailing torque to run the bolt down might be affected. That is why it is just common sense to run the bolt down by hand completely to make sure it is engaging, that the joint is pulled down to zero clearance and that the new threads are exercised prior to starting the torquq-angle sequence.

BIGGUN
06-17-04, 04:02 PM
Don't know if it's relavent or not but through the first sequence and then partly through the second everything felt the "good". In the middle of rotation in the second sequence the tension it took to turn the wrench dropped off significantly and never increased again even through the third on the trouble spots.

The same bolt tried in a different hole felt soft and a bolt that felt good in another spot, installed where the problem was, bolted up fine also.

I just figured I'd give some more info on the situation.

Thanks Geno,
Kevin