Procedure for re-torque of head (searched...)

[SleeperZ]

I've heard mention that after a new install of a head gasket, the head should be re-torqued after getting it running and hot.

 

I've just installed ARP studs, torqued to the ARP recommendation of 60 ft-lbs with ARP moly lube. How do I retorque this beast? Do I loosen all the nuts, regrease them and retorque in the proper sequence? Or just apply the torque wrench again (in the proper sequence)? I'm concerned the lube on the threads is gone now, and I could over-torque the nuts if they aren't re-lubed...

 

TIA,

Nathan

[BayAreaZT]

I got this from another forum a while back supposedly from ARP

 

 

"The lubricant used is the main factor in determining friction, and therefore, the torque for a particular installation. Motor oil is a commonly used lubricant because of it’s ready availability. If less friction is desired in order to install the fasteners with less torque, special low friction lubricants are available. With special lubes, the required torque can be reduced as much as 20 to 30 percent. It is important to keep in mind that the reverse is also true. If the torque value has been specified for a particular fastener on the basis of low friction lube, installing the fastener with motor oil will result in insufficient preload; the torque has to be increased to compensate for the extra friction caused by the motor oil."

 

also...

"The friction factor changes from one application to the next. That is, the friction is at its highest value when the fastener is first tightened. Each additional time the fastener is torqued and loosened, this value gets smaller. Eventually the friction levels out and becomes constant for all following repetitions. Therefore, new fasteners should be tightened and loosened through several cycles before applying final torque. The number of times depends on the lubricant. For all situations where ARP® lubricants are used, five cycles are required before final torquing."

 

I don't think you have to re-lube. Just back them out and re-torque.

[Here comes trouble]

do not loosen the head bolts....with a "click it" tourque wrench start out in the tightening.sequence with 33 foot pounds and progress to 47 pounds and then to 61....This way you will discover which bolt(s) if any lost it's total tourqe....How are you going to discover if any bolt lost it's tourqe by loosening them all up and possibly damaging your gasket which in most cases usually can be compressed only once.?????????????

[1 fast z]

Loosen them up a quater turn, then retorque to the desired spec.

[Tony D]

If anything, the torque required the second time will be LESS if the lubricant is gone. The lube makes it easier to torque, and if it's gone, you undertorque the fastener.

 

The most common cause of failure on engineered fasteners or yield-type fasteners is using the wrong lubricant, resulting in less turning friction than designed, and overtorquing causing failure.

 

Atlas Copco used standard bolts in 3 of 6 designs. Those three had Loctite on the threads. On the other 3 designs, they had a "stretch bolt", and it was engineeered to go in DRY. When field personnel applied the "two drops of Loctite 242, just like everything else" the bolts were overtorqued, and would fail in service within 4000 hours. I can't remember HOW many warranties I declined over that decision to not read and follow manufacturers' instructions...

 

That segeues into reading the instructions. The Nissan Retorque criteria is to loosen and retighten them. I would e-mail ARP for a specific recomendation on their procedure if it is not spelled out explicitly in thier literature.

 

Normally retorque is a gasket manufacturer's requirement. If the gasket has compressed under a fastener, and it turns when you go to check it with a click-type wrench THAT is how you know what one is loose. Otherwise the bolt will just stay there and "click". The degree of rotation before clicking on the retorque will tell you compression! For most gaskets, I just go back and check torque at the setting required.

 

The point Bay Area posted makes a good thing to consider, also! Normally you will run the bolts down several times and back off several times during mockup of the engine so the fastener is settled down to it's "real" turning torque by the time of final assembly. Technically you are to take turning torque, and ADD it to total torque required to make sure you don't undertorque a fastener. Not usually a problem, but on larger things where you have coarse threads, the turning torque can be considerable.

 

On stock stuff, it gets broken free, and retightened simply because of the bolt breakage issue on stock bolts.

 

Hope this helped somewhat. Good Luck.