Retorquing Head Stud/nuts - Why????

[PaulRV6]

Can someone explain the reasoning behind retorquing the head stud nuts a couple of times after initial tightening?
Ya go thru the process of torquing the nuts in sequence up to the required value (in small increments) and then ya loosen each one (one at a time mind ya) only to torque them back to the riginal value but in a single twist? I don't get it.
I am using ARP stus/nuts not for the first time (re-used) so is this still necessary?
I did perform this sequence (not sure why and not really wanting to) but did it anyway. Just seemed kinda crazy.
If someone could explain this for me and if it is really required. Thanks

 

[Joe 1320]

The gasket compresses when you torque the heads down and even if you release the torque, the gasket never comes all the way back to it's original uncompressed height. Retorquing ensures that the gasket is fully compressed and wont shift after heat cycling.

 

[S10xGN]

I know this isn't exactly what you're asking, BUT -

ARP recommends this for NEW fasteners - simply to "bed" in the washer and nut/bolt head faces. This reduces the torque wasted on friction between these surfaces. IE - the first torque cycle might have 30 - 40% of the value overcoming the friction between surfaces, leaving only 60% for clamping while each successive cycle may reduce this by 5%. So after 5 torque cycles, you may only be wasting 10% on friction and devoting 90% to actual clamping. NOTE: above numbers are *conjured up* only for explanation purposes!

HTH,

 

[Kid with a toy]

If it's one thing Russ is an expert on, it's head bolts. He's had to put on and take off more head bolts in the last year than most do in a life time.

Russ, when are we going to slap on that truck bed

E-mail me.

Erik

 

[Intercooler]

See if the links in this thread I posted makes sense:

http://www.turbobuick.com/forums/showthread.php?s=&threadid=48205&highlight=retorque

 

[Fred 86 GN]

Heat cycling.

The most important reason to re-torque the head bolts is to compress the head gasket just a little more AFTER the engine had been ran a couple times at least and brought up to temperature each time. This is more critical with aluminum heads than with cast iron, since the aluminum has much more thermal growth than cast iron.

If you do not push the car or detonate it, the retorque is not so critical IMO.

I did it last time. So far so good.

 

[bob86gn]

How about the bolts that are in the water jacket and are teflon sealed. Will the teflon still seal after being cycled a couple of times?

 

[Intercooler]

It should be fine. If you use composition gaskets I don't think it is needed to re-torque. If it makes you feel better though, go for it!

 

[bob86gn]

Thanks Jesse. It seems like getting heads to seal is close to vodoo!