overtorqued wheel bolts: what to do

[Wayne County Hose]

Prevalent in this post, and many in the thread, are extreme statements. Problem is, to a little cooler analysis they never always hold up. Take the one above. It will get you in real trouble to err very much on the loose side because if the fastener is employed in a demanding situation its tightness becomes paramount. If its loose the joint will squirm around, wearing the joint and the threads, and backing out the bolt. A hi strength bolt in such a situation can severely damage the parts it is holding, especially when several fasteners are meant to be holding evenly- loosening of one allows prying against those adjacent. Strong bolts can break castings in this way. Assuming the joint is correctly designed this would not happen if the speced torque, or in many cases a few % above spec were used. I say "in many cases" because seldom are bolts employed to their max, where they are torqued to yield [plastic deformation], and are not to be re used. Connecting rod endcap bolts are sometimes speced to be used to this level, and the wise person replaces them, but the less wise usually gets away with reuse. --- Our tractor uses usually spec torque well short of yield for the appropriate fastener, leaving a significant margin of unused capability. In particular, with things like wheel lugs and loader mount bolts, thats why the experienced mechanic can work with a familiar impact wrench. Hes playing in that "about right" area which can actually extend more above spec than below it. You wont find him doing it with your head bolts or rod caps tho.

larry​

There are so many erroneous statements above I just don't know where to start. What is extreme is when people say that they can torque a bolt with an air gun and get it "about right." My compressor kicks on at 110 lbs and off at 130 lbs. That's almost a 20% difference in torque output. And to think that you can feather the trigger to get the torque you want is just ignorant. I have tried this with other mechanics. Try torquing a bolt to what you think is 100 ft lbs., then take a good quality torque wrench (not a Craftsman either) and see how much torque it takes to turn the bolt. I'll bet the farm that 9 times out of 10 that you are not within your torque range.

Connecting rod bolts are not spec'd to torque. They are spec'd to stretch. The engineers use a bolt stretch gauge and tighten them until they get the proper amount of stretch for the grade and size bolt they are working with. They then see how much torque was applied for this amount of stretch. They give a torque value because we don't walk around with bolt stretch gauges in our pockets.

This is why I stated that overtorquing a bolt does more damage than undertorquing does. When you torque a bolt, you stretch it. When you overtorque it, you overstretch it. You actually tear the particles of the bolt apart, which, of course, weakens it drastically.

As far as a loose fastener doing damage goes, if you never check your equipment and overtighten fasteners so you think you don't have to check them, you are setting yourself up for disaster. If you have bolts that frequently come loose, you have a problem. Overtorquing will not solve the problem. This is why, to obtain a cdl, when you do your pre-trip inspection, you are required to physically put your fingers on every nut and bolt on the truck that if that fastener should come loose, would result in a catastrophic failure. They don't say to overtorque it and never check it.

Having been certified as an A+ service technician in my field, I will say that any "mechanic" that torques things down with an air gun or uses overtorquing as a way of problem solving is nothing but a rank amateur and should find a desk job.

 

[SPYDERLK]

There are so many erroneous statements above I just don't know where to start. What is extreme ...

Actually there are no incorrect statements in the post you refer to. What is extreme is your fixation on negative interpretation and exaggeration of all statements that do not agree with a worst case scenario of incompetence.

larry​

 

[megaboz]

I can't help but chuckle. Everyone is getting very excited.

I agree over torqueing is bad, it damages the bolt and possibly anything in between or the threads on both the bolt and nut, under torqueing is bad, the bolt will come out and the other bolts do more work.

I think the under-torqueing statement was not referring to leaveing the bolt loose, but not over tighten. An overtighten bold is weaker because it has been stretch and will/could break. Where an "under-torqued" but not loose bolt will not be brone to breakage, extra wear maybe, cut through by the surrounding metal, probably too.

Impact wrenchs don't have a guage, and there is no way that someone can guess the torque from an impact gun, you might be able to throttle it down with the built in clutch if it has one, but it is not perfect. I've seen guys that just keep hitting for another 10 to 20 seconds after apparent bolt movement ends. From experiences getting stuck bolts loose, I know if I keep hammering on it it will loosen.

Also keep in mind that the metal that has the bolt through it may not be able to handle a little more than spec.

It is hard to find a "good" mechanic (they're the rarest of all tradesman), and when I do, I stick with them.

Before anybody jumps me, I am not saying anything bad about anyone who has posted nor implying anything.

 

[Wayne County Hose]

I am going to change my screen name to Mr. Negativity just so all of you know who it is when I post.

 

[crazyal]

I guess over torquing the lug nuts would be better than over torquing the head bolts but neither is good. You could ask the dealer to come out and loosen them up for you then correctly torque them, maybe when they are in your area. Not knowing how tight they are it's hard to know if any damage was done. With cars over torquing the lug nuts can do damage to the rotors and flanges as well. It's possible that it's not just the extra torque but also any rust that formed on the threadsthat's giving you problems. Either way I would use never-seize (or anti-seize) on the threads.

 

[Egon]

I am sorry of the problems many of you have faced with torque problems!

How many have a reliable torque wrench??

I have an impact wrench that is so famous it dose not even need a name brand on it.

So far it has served me well on the lug nuts from the tractor, car, trailer and the truck. Am I missing something???

 

[TalonDancer]

...I have an impact wrench that is so famous it dose not even need a name brand on it.

So far it has served me well on the lug nuts from the tractor, car, trailer and the truck. Am I missing something???

Depends....
on whether you happen to have your famous impact wrench (and air compressor and power source) handy EVERY time you need to remove those lug nuts.

Talon Dancer

 

[Egon]

No its not always available but there does seem to be a 1/2 in breaker bar with the appropriate socket and a two foot snipe on hand!

 

[Fjord]

If you don't feel like buying a big breaker bar , just get one of those el cheapo adapters that increase from 3/8" drive to 1/2" or 1/2" drive to 3/4" ($2 or $3) and weld it on to a piece of 1/4' X 1 1/2" flat bar about a foot or so long and then slide as long a piece of pipe as you want over it. It's very strong and doesn't flex at all.

 

[SPYDERLK]

I guess over torquing the lug nuts would be better than over torquing the head bolts but neither is good. You could ask the dealer to come out and loosen them up for you then correctly torque them, maybe when they are in your area. Not knowing how tight they are it's hard to know if any damage was done. With cars over torquing the lug nuts can do damage to the rotors and flanges as well. It's possible that it's not just the extra torque but also any rust that formed on the threadsthat's giving you problems. Either way I would use never-seize (or anti-seize) on the threads.

Overtorque is relative. Theres a little or a lot. A lot, Im guessing in the neighborhood of 20%, will stretch a bolt past its elastic limit [to yield]. Only situations where a fastener is not meant to be re used are speced for a torque this high. You are flirting at the upper limit of bolt strength and have "modified" the bolt to get there. The metal crystalline structure moves at yield and the crystals find firmer lock points. This makes the bolt stronger as it is "failing". This gives a usable area above initial yield. The bolt doesnt just snap if the load increases. Fortunate, but lets try to avoid playing in that region. The point is that it is there above the torque speced in conventional use. Its why people get away with tightening things above the conventional spec in good solid steel on steel applications, and the elimination of squirming is why they stay tight. Any movement trys to cock the bolt [the Pythagorean triangle is no longer 0 degrees] thereby also trying to stretch it beyond the original elastic stretch imposed by a conservative application of torque. This movement induced stretch may be large enuf to cause the bolt to yield. At the very instant this begins the bolt becomes stonger - preload is UP. However since the joint has moved. the bolts tension axis is slightly skewed from original and the tension on the bolt has a component favoring movement back to original. If it moves back the original preload has lessened - the bolt has loosened w/o turning. The movements repeat. You probably dont hit yield again since the bolt is now long enuf to allow full range of motion to the point that the head slips sideways to follow the movement. What you do have is wear on every moving part accompanied by a natural backing out on the helix. A lock washer sometimes grabs enuf to prevent the turn, but the wear continues. The bolt "loosens" w/o turning. To say that you are responsible for maintaining tightness is certainly true, but if the bolts are needing retorque repeatedly, it may give you some feeling of usefulness to do it, but frustration and alarm are more appropriate. The joint is not truly up to the load it is carrying. It is in an extended failure mode. With steel/iron joints a 10% torque above spec will likely stop the cycle. New bolts, stonger if readily available - and use of hi strength flat washers, are added insurance. Ample thread engagement in castings is a must.

Most torquing is meant to be done dry - sometimes with oil. It will be speced. Lubes will cause unexpectedly hi preload per unit torque, may thus strain the bolt -- and otherwise favor unwanted loosening in cyclic use due the reduced friction. Anti sieze on lug nuts is very risky. An occassional spray of WD40 after assembly should keep rust out.

Gasketed joints are different. Uniform tightening and retorquing is necessary. Even fairly small torque excess can be dangerous to the assembly.

larry​