A lot of the fastners on our vehicles require fairly accurate torqueing (tightness) to perform properly and safely. Since a lot of the work I do here at home is seldom with all new fittings, I'm wondering if one should compensate for older or rusty threads? (more torque) OR lubricate and use less torque?

Case in point, I had my 8 lug aluminum wheels off yesterday, and the lug nuts and studs seemed kinda dry, and difficult to remove. Had to use a wrench most of the way off.(yes,by hand,waitig till X-mas for that new impact wrench) Now it wasn't very hard, but I couldn't spin them off with my fingers. SO- upon reinstallation I lubed them up with a shot of WD40 and a dab of grease. When I went to torque them down to spec (100fp) it seemed maybe too tight (the lube worked really well).
Also, not to long ago I had to remove a manifold stud nut that was rusty. It came off OK, and went back on OK, but it took a wrench and some effort to put it on. (again with WD40)

SO, my questions are this- Should torque be adjusted acording to conditions like these? (more for hard parts, less for lubed ones)
Are factory specs calculated for new unlubricated parts?

I believe that with all the aluminum and light weight materials going into todays vehicles, that proper torqueing is more inportant than ever.

Seems to me that well lubricated threads will turn much easier, and therefor require less force to get them to a given tightness (clamping force). Just like a fine thread bolt will clamp tighter than a standard bolt will at the same torque. After all, it's the clamping force we're trying to accomplish, using torque to get there.

Any thoughts on this? Thanks, Rob

 

Rob,

You bring up some interesting points...ones that I've never thought too much about until now.

My guess would be that since you're cleaning and lubing the fastener before reinstalling, that the specified torque would be accurate, providing the torque wrench is accurate. I'd say the specified torque applies to a clean, properly lubricated (or just clean) fastener. I use a dab of anti-seize on all wheel lugs and any other fastener that might be in danger of becoming hard to remove over time, before torquing.

I'm sure there are some engineers and folks with way more experience than mine who will be glad to add their opinions to this thread. I haven't experienced any failures with my torquing methods yet...so unless someone can show me the error of my ways, I guess I'll continue as I have.

Regards,
Scott

 

I recall reading something about oiled versus non oiled bolts on engine headbolts regarding torque. I oil or use anti-sieze on everything I put back together. I hate rusty threads.

 

Yup, torque specs are for clean lightly lubricated threads. John Deere tech has a school manual for mechanics that is specialized dealing with fastners. Its worth reading. Bolts can dry seize and friction weld together, permanantly fastened. A lot of times you think a lug nut is rusted on, many times it dry seized during installation. This happens a lot at tire stores, they zip the nuts on at hi speed, the heat and pressure welds them right on. Run them up slow with the gun. We oil every bolt we install here. I like Aero-Kroil better than WD-40, its a little oiler and comes out of the can a drop at a time if you want, but anything works. I dont use never sieze on wheels as its just too messy and slow, just a little shot of spray. On a National Coarse bolt about 40% of the torque is used up in thread friction, a dry bolt would go higher and will reduce the applied tension that the fastner is designed to provide. Use oil unless there is specific instructions not to.

 

> Are factory specs calculated for new unlubricated parts?

Yes, though some are for lubed parts with 30 weight oil. It depends on the part. I usually use anti-seize and go for the lower value, except for internal engine parts, then I go strictly by the book.

On non-critical parts, bolts for MAP sensors as an example, I use anti-seize and then go hand tight because no way am I going to get an accurate reading on a bolt so small with anti-seize nor am I going to waste my time using a torque wrench for it.

On some parts that come with anti-seize on them (02 sensors) where you are not suppose to put anything on the threads or connectors, with pipe threads, I do good-n-tite because getting a torque wrench in there is impossible and they give the torque specs just to make the OEM engineers feel good.