check your lug nuts + torque wrench madness

[xtn]

Unless the lugs/studs we're talking about are made of butter, the amount of heat they're exposed to will absolutely not result in any stretching.

I don't know much about exactly how much stretch a particular fastener might have at a particular temp increase, but I do know that everything in the known universe is elastic to some degree.

In fact if bolts didn't stretch the whole concept of putting a torque wrench to them would be useless. As soon as the nut bottomed out it wouldn't turn any more. Applying additional torque is for the purpose of using a defined amount of stretch to provide additional clamping force to the items being bolted together. In some cases the required torque is such that the bolts are stretched beyond their yield tolerance, such that they become permanently stretched and should not be reused if they are ever removed.

Most of that engineering stuff is over my head, but I am aware of it. Saying that a bolt absolutely won't stretch with a little heat, while subject to some stretching force, cannot be accurate. Maybe in this application it wouldn't be enough to matter; I can't argue that. But it is possible they could stretch.

 

[sparc]

In many applications as I am sure most of you are aware bolting gets replaced after so many uses or even after one use (torquing). In some large bolting applications I have seen the studs are hollow and an electric heater is inserted into the stud to raise the stud temperature to what will be the operating temperature when in service. Then the studs are tensioned (not torqued) until they stretch an engineered distance; the nut is then run down the thread by hand and hand tightened then given a light snugging with a wrench (again by hand) and then the tension is released from the stud. This was on 6" diameter studs on a pressure vessel with an operating pressure over 600 PSIG.

As was said every time a fastener is tightened it is stretched slightly and it never returns back to its original dimensions. Eventually it will be come so elongated it can not met design specs and must be replaced.

 

[two_bit_score]

In many applications as I am sure most of you are aware bolting gets replaced after so many uses or even after one use (torquing). In some large bolting applications I have seen the studs are hollow and an electric heater is inserted into the stud to raise the stud temperature to what will be the operating temperature when in service. Then the studs are tensioned (not torqued) until they stretch an engineered distance; the nut is then run down the thread by hand and hand tightened then given a light snugging with a wrench (again by hand) and then the tension is released from the stud. This was on 6" diameter studs on a pressure vessel with an operating pressure over 600 PSIG.

As was said every time a fastener is tightened it is stretched slightly and it never returns back to its original dimensions. Eventually it will be come so elongated it can not met design specs and must be replaced.

Commonly known as 'worn out'.

 

[RoyJackson]

I put about 150 miles on a new trailer, and remembered to check the lugs last night. At least one lug on each of the four wheels took an honest half turn before tripping the torque wrench at 95 ft-lb. The rest were OK.

Oddly, my torque wrench stopped working about halfway through the job. Couldn't figure out why this would happen, since it was working fine last time I put it away.

Well, I took the ratchet head apart, examined everything to figure out how it worked, and found the problem -- whatever grease had been in there was all gummed up and had turned into varnish. This was preventing the ratchet mechanism from working, and it was stuck in a free wheeling position. I cleaned everything out, put new grease in, and went back to work.

And that's how a simple one-minute check of 20 lug nuts turns into a messy 30-minute job. Story of my life. I don't know what kind of lubricant Craftsman put in that ratchet mechanism, but it sure gummed up pretty bad. The wrench is about 14 years old.

After disassembly, you should have it calibrated, or at least verify it against another torque wrench (that you know is good).
Calibration is preferable, but if not possible, use the other (known good)torque wrench and torque a fastener to a given torque. Then set your reassembled wrench to that same torque and see if the fastener moves. Better to set torques two or three settings in the wrench's range and ensure it's working correctly throughout the range. Again, not the best way...but it works.
This actually works better with deflecting beam or dial indicator torque wrenches, IMHO.

 

[RickB]

After disassembly, you should have it calibrated, or at least verify it against another torque wrench (that you know is good).
Calibration is preferable, but if not possible, use the other (known good)torque wrench and torque a fastener to a given torque. Then set your reassembled wrench to that same torque and see if the fastener moves. Better to set torques two or three settings in the wrench's range and ensure it's working correctly throughout the range. Again, not the best way...but it works.
This actually works better with deflecting beam or dial indicator torque wrenches, IMHO.

I still don't understand why all the panic about the wrench calibration after having the ratchet apart. The ratchet mechanism is entirely separate from the torque sensing mechanism. He could have welded the ratchet mechanism solid and it would still sense torque as good or as bad as it did before.

 

[RoyJackson]

I still don't understand why all the panic about the wrench calibration after having the ratchet apart. The ratchet mechanism is entirely separate from the torque sensing mechanism. He could have welded the ratchet mechanism solid and it would still sense torque as good or as bad as it did before.

Just good sense, Bro...check the accuracy of your tools, especially after any kind of disassembly.

 

[RobertN]

Cause I hate having to tear stuff apart to get at a broken bolt and try to extract it... Cause it is always in the absolute worst spot for access etc.

I still don't understand why all the panic about the wrench calibration after having the ratchet apart.

 

[RobertN]

Old grease can gum up like that. I have seen it in $10,000, $20,000+ microscopes. Nikon, Leica, Olympus... The greases just dry and harden over time. A few years back, a group at work was ready to scrap a really expensive microscope. It was a few years old, but was still an excellent microscope. I had my microscope service guy do an annual on it for $200; scope worked great. He had to scrape the dried lube off some parts.

And that's how a simple one-minute check of 20 lug nuts turns into a messy 30-minute job. Story of my life. I don't know what kind of lubricant Craftsman put in that ratchet mechanism, but it sure gummed up pretty bad. The wrench is about 14 years old.

 

[SPYDERLK]

I still don't understand why all the panic about the wrench calibration after having the ratchet apart. The ratchet mechanism is entirely separate from the torque sensing mechanism. He could have welded the ratchet mechanism solid and it would still sense torque as good or as bad as it did before.

......:thumbsup:

Just good sense, Bro...check the accuracy of your tools, especially after any kind of disassembly.

.......:confused2:

Cause I hate having to tear stuff apart to get at a broken bolt and try to extract it... Cause it is always in the absolute worst spot for access etc.

........:confused2:

 

[RickB]

Just good sense, Bro...check the accuracy of your tools, especially after any kind of disassembly.

You miss my point. The wrench either is within calibration spec or it isn't. Disassembling the ratchet doesn't affect calibration in the least.