[Dees67]

Is there a rule of thumb for how much to reduce a torque spec
when using lube on the fasteners?

 

[bchampion]

Depends on what you are using, the mfg. should state the torque multiplication factor to arrive at the correct torque value. I use to work with tool joints alot and the torque value would decrese or increase depeding what type of pipe dope used. For example, we use this thread locking compound called Torq-lok on some of our high stressed connections (BTW DO NOT USED THIS STUFF ON ENGINE FITTINGS BECAUSE YOU WILL NEVER EVER BE ABLE TO GET THEM OUT) and we would have to multiply the torque by 1.25.

 

[Guest]

Don't know, but I think that for major fasteners, the torque spec is for a lubed fastener, not unlubed.

 

[BillScott]

installing my Canadian Mustang "Big Kit" i used central values on the new hardware with antiseieze compound such as spec value in Shop Manual is 75 - 105 which i set at 90 for strut to lower arm. Osborne Manual specs a mean of 90 and a standard deviation of 5 which would fit 3 sigmas of 75 to 105 consistent with Shop Manual. i had a little problem with Osborn Manual when they spec'ed sway bar nut at a mean of 7.6 and std dev of 0.03 (all in ft-lbs) - some new mechanical engr exhibiting his knowledge but lack of understanding of statistics.
a further question i have is on sandblasted bolts and nuts which when roughed up seem harder to turn - i just applly light oil and use manual values and only use new hardware on critical items.

 

[Ray_Hillebrand]

Most torque specs stated are assuming the threads are clean and lubricated...

 

[Brightman]

I understand most of the torque applied to a fastener is used in overcoming the friction of the threads against each other, so lube has a large effect on clamp load attained with a given torque. Visit here http://www.arp-bolts.com/pages/tech/images/fasttorq.pdf for more info from ARP.

 

[camachinist]

No rule of thumb...depends on fastener type, thread pitch and lube type..

Most fastener mfg's, such as the ARP guide you were referred to, have specific guidelines for their fasteners, but these are not universal.

If you can't find information on your fasteners online, post the specific sizes, pitches and grade #'s, along with the lube you are using and I can get you into the ballpark.

 

[JohnS_65KGT]

Maybe I'm being stupid here but from a logical point of view the torque is a measure of how tightly the parts are being held together right? So I dont understand how lubrication would make any difference in how tightly these parts should be torqued, If anything the pressure exerted at 60 ft-lbs on two parts by a lubricated bolt would just be closer to what the engineers had in mind since I'm sure they were working with brand new clean fasteners. Now rust or banged up threads of course could require a higher torque due to having to over come friction but then you run into a risk of over stressing the fastener.
I certainly do not have the experience of most of the people here but I have never had a problem with using the specified torques with resonably clean fasteners lubed or unlubed. I always come back and recheck the torque after a while anyway to make sure they have not loosened up on me due to vibration or settling (or stupidly missing one). In short I would make no adjustments to the torque for lube. In fact I would be concerned that lubing and under torqing could case them to loosen up easier.
I'm always willing to learn so if I'm off base somewhere plz enlighten me.

John