What tightening torque do you apply when using anti-seize? Torques given in workshop manual apply to dry bolts unless otherwise stated ('bolt lightly oiled') but I read somewhere that when anti-seize (or lubricant) is applied to the thread torque should be decreased by 20%? What do you guys do?
Other question, silly probably but I have to ask - what means 20 + 3 Nm? Apply 20 Nm force in first step and then 23 in second one?

 

Are you thinking about certain bolts in particular?
On these cars I don't think I have ever used anti seize when bolts were to be tightened to a certain torque value.

Yes, 20+3 means 20 first pass, 23 second pass.

 

I was thinking about everything that is under the car. I got a real fun trying to take apart suspension. Even bolts in engine bay were seized.

 

Torque values assume dry/un-lubricated threads. As soon as you add anti-seize compound, the torque value will be incorrect.

When I've used anti-seize on threads, I generally tighten by feel, but I only do that on nuts/bolts like exhaust components, etc. I try not to use anti-seize on a bolt going into aluminum because there is too much risk of pulling the aluminum threads out. In those cases, I wire-brush the bolt so that it's clean, then chase (tap) the threads in the aluminum, then assemble dry to factory-recommended torque specs.

 

Lubricating bolts going into aluminum is a bad idea then. I will refrain from doing that but steel bolts in suspension are so tempting... Whoever stripped down 25 years old suspension will agree with me I think. So anti-seize them and decrease torque by 20% or other value or just leave them dry?

 

The Porsche factory manual says to lightly lubricate the threads when installing the cylinder head nuts. I haven't researched other steel to steel fastener interfaces in the factory manual.

For steel to aluminum joints, the manual mostly specifies loctite 221, then torque to specified value. Some steel to aluminum fasteners, the manual does not specify loctite, so I guess you could assemble dry on these, but I am personally more afraid of dry fasteners galling than I am achieving incorrect torque, so I use light oil or anti-sieze and hand tighten to my "calibrated" hand-torque sense of what is right.
Clean threads are very important as has been noted.
I always use anti-seize on water pump hardware and studs. I always use loctite on the plastic belt shroud hardware because I don't want one of those little bolts backing out and falling into my timing belt and taking it out.

 

Correct, and this is allowed because the factory torque procedure for head stud nuts doesn't involve using a torque wrench. If it did, they would tell you NOT to use any lubrication because that would render torque wrench readings incorrect.

Torquing head nuts is performed using a series of 90-degree turns with a standard wrench. A torque wrench is not used and no torque value is provided.

 

I wont opine on what you should and shouldn't use anti-seize on, but I'd stick with the 15-20% reduced torque plan if using AS.

 

Please be careful about giving misinformation here. The original procedure from Porsche specified lightly lubricating the threads of the studs and then torque in three passes. Even after they changed to the 90-90 update, the procedure still involved the first pass being torqued to 15 lbs-ft, then 90 degrees and 90 again.
Even when specifying loctite, Porsche instructs to lightly lubricate the threads.

 

Correct - the original torque specs for the 944 engines were given in N-m (ft-lbs) in the FSM, and it did include the same full oiling/lubrication note (at least as of the 1985 printing). The FSM did not revise the torque specifications to the torque angle method until 1991.

 

The torque is the torque, meaning if you tighten a bolt to 20 ft-lbs, the bolt is seeing a torsional stress induced by 20 ft-lbs, regardless of whether it is lubricated or dry. So you will not twist off the head of a bolt because of using anti-seize. What you do is decrease the frictional component of the resistance, so you increase the clamping force (tensile load on the bolt, and somewhat the shear stress on the threads). But this is typically not a problem for most bolted applications if using the specified bolt grades and not exceeding the stated torque specs (as the factory torque specs are well below the yield or proof strength of the bolt), probably desirable in most instances - except for gasketed joints, like the head gasket, where you want a specified crush.

So with that said - to help reduce galling and corrosion, I use anti-seize on nearly every bolt on the car (when Im not too lazy to apply it), and never reduce the torque spec value. For what its worth, I have never broken or damaged a fastener because of that, and it has been 20+ years on multiple 944 series cars.

 

even on bolts/studs going into aluminum? never had any problems with broken thread? this is something that i would like to avoid. i'm sure now i'll use anti-seize on suspension components.

 

I know the OP wanted to know "what do you guys do?" After the dust settles, here's some info that may help. BTW, if you believe the info below, the risk of pulling the threads out of aluminum is real.

http://www.marylandmetrics.com/tech/data1torque.html

http://sw-em.com/anti_seize.htm

http://www.portlandbolt.com/technica...que-chart.html

http://benmlee.com/4Runner/threads/threads.htm

 

Ummmm......no.

 

Agreed.
It is not only the torsional force on the bolt, it is also friction of the nut/bolt and threads. If you change the friction, the amount of torsion on the bolt also changes. Changing anything in the assembly process or changes in the bolt (plating, metal properties etc) has an effect. Makes on wonder how this works at all. I guess that is why some engine builders measure the stretch on rod studs to get the proper tension.

The basic formula T = K x D x P stated earlier takes these factors into account and provides users with a starting point for establishing an initial target tightening torque.

• T -Target tighten torque (the result of this formula is in inch pounds, dividing by 12 yields foot pounds
• K- Coefficient of friction (nut factor), always an estimation in this formula
• D -Bolts nominal diameter in inches
• P - Bolt's desired tensile load in pounds (generally 75% of yield strength)

The only way to properly determine the optimum tightening torque for a given application is to simulate the exact application. This should be done with a tension indicating device of some type on the bolt in the application. The bolt is tightened until the desired P (load) is indicated by the tension indicating device. The tightening torque required to achieve the desired tension is the actual tightening torque that should be used for that given application. It is extremely important to realize that this tightening value is valid only so long as all of the aspects of the application remain constant Bolt suppliers sometimes have customers say that their bolts are no good because they have started breaking while being installed. Thorough investigation commonly reveals that the customer has started lubricating the bolts to make assembly easier, but maintained to same torque as was used when the were plain finished.

http://www.zerofast.com/torque.htm