I just had a torque wrench malfunction. First time ever and in a tough spot

I was using an expensive Precision Instruments split beam torque wrench installing a clutch on the end of a crankshaft. I went past the specified torque by a good 1/2 turn at least and still no click. Removed wrench, went to vise to test and sure enough, it was stuck. Worked it back and forth on Vise and it got back to clicking properly. Wow, now I'm not sure whether to leave bolt in it as is, or try to remove and retorque. The threaded part of bolt is a good 6" deep in the crank. Breaking the bolt of in it is not an option!

That is a conundrum...let your conscience be your guide!

I had a similar experience, but it was an electronic Snap-On torque wrench...and I was not so lucky. Little did I know, as I pushed on the handle, the wrench powered off...I kept pushing and pushing waiting for the beep...instead of the beep, I snapped off the shaft of the A/C compressor that I thought I was torqueing the clutch on. I swore off battery powered torque wrenches that day!!

If it isn't a torque to yield bolt I think I would be inclined to loosen and retorque it.

The only torque wrench I ever had stick like that was my first MAC and it did so because I forgot to loosen it after use. The MAC tool guy sent it back for repair and calibration. I never forgot to loosen after use again and it still works as new. It is 49 years old now.

NH575E said:

I would be inclined to loosen and retorque it.

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I really think it will snap if I try to move it at this point. I'm a good 50% beyond spec. I've decided to go with it for now. Maybe it will stretch a little along the way? I reset all my torque wrenches back to 0 every time, but the split beam type doesn't require that.

If I'm reading your OP correctly at a half turn beyond spec I would say the bolt is very close to breaking point. The best time to get it loose is right now. It ought to come right back out provided you put wieght on it slowly without snatching at it. When you do get it out throw it straight in the bin and fit a new one.

TBH I'd be frightened of what could be the consequences if the bolt broke while the machine was working.

Nige said:

It ought to come right back out provided you put wieght on it slowly without snatching at it.

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Thanks Nige, you're probably right, but if that bolt shears, I'm screwed!

I have my fingers crossed for you.

JL Sargent said:

Thanks Nige, you're probably right, but if that bolt shears, I'm screwed!

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If you take the bolt out and it shears you're screwed, but if you send the machine out to work and the bolt shears, you're double screwed. And if you take the bolt out and it's OK, you can get on with your life without the knowledge forever preying on your mind.

I'm with the remove and replace with new bolt crowd. Not knowing the details of this clutch mount if that bolt does break I would not want to be around.

I think there is a very good chance the bolt if it has stretched that much it might actually be holding less than if it was properly torqued, something about the elastic limit of the bolt.

I also hope that this clutch is not on a tapered shaft because the over torque on the bolt could cause something to crack and come apart.

Just because one over-torques a bolt doesn't mean its close to failing. IME, a torque spec does 2 things, prevents something from deforming and prevents something from coming loose.

I'm with Nige, remove and re-torque.

Ed

How big of a bolt and what kind of torque specs are we talking about? Is this a 1" drive torque wrench at 600ft. lbs or 3/8" drive at 75 ft. lbs instead of 50?

I looked online and found a precision instruments torque wrench, but it was only 1/2" drive.

im with the remove crowd, like nige said remove slowly , replace bolt, i would loosen all of the bolts and retorque. if you leave it and it breaks while running it may jam in the clutch and things could go bad fast

I usually end up with stripped threads rather than broken bolts

Been eyeing my old torque tools quite intensely of late, even as were within spec on a tool truck they are well over thirty years old and could fail at any given point. HOWEVER listening to these type events I am not comfortable with the 'Now In Style' type torque wrenches, may end up buying a torque meter that installs between ratchet and socket as have found out my aged torque wrenches are no longer supported.

DMiller, You are correct, we are a bunch of old mucks, and our tools are getting quite old too. I wouldn't trade or sell my tool box full of tools for anything...Tools are for buying not selling!!!

Anyhow, you have made me think, hmm, I have not had my Snap-On click type torque wrenches tested in a looong time. My newest torque wrench was the 3/8" digital, and it is gone! So, I looked on the internet, and found some sites that give you step by step on how to test the accuracy and adjust. I also found sites that offer calibration services. Honestly, what I was looking for was Snap-On's calibration service. I know years ago the tool truck guy would take your torque wrenched and send them out for calibration, and that is what the Snap-On site says today "Give it to Snap-on and we'll make all the adjustments it needs, clean it up, replace worn handles, and have it back to you in no time"
I think I will contact the Snap-On salesman that services our school and discuss this with him. Since I am not in an actual shop that the truck comes to, it makes it more difficult. In the meantime, I may just give the step by step how-to a whirl, if for no other reason but to see if they are close.

I have always stored my torque wrenches in the blow molded plastic boxes and the value backed all the way down. It will be interesting to see if they are still accurate. I think the fact that I do not use them professionally (not to often) will help them to remain accurate.

Found this on several sites:
The actual "Click" from a wrench is considered a "Cycle" of that wrench. Most manufacturers recommend click-style torque wrench calibration after 5000-to-7000 cycles.
For most customers, this means you should calibrate and test torque wrenches every 12 month


How-to sites:
https://www.wikihow.com/Calibrate-a-Torque-Wrench
https://www.finepowertools.com/hand-tools/torque-wrench-calibration/

Sites that calibrate:
https://jmtest.com/torque-wrench-calibration-service/

https://www.fastenal.com/en/1487/calibration-and-repair
https://atslab.com/calibrations/sna...ibration experts who have years of experience.

https://cscforce.com/torque-wrench-...utm_content=Torque Wrench Calibration Service

It's been a while since I compared my old MAC wrench to another but the last time I connected it to a new Snap On dial wrench it clicked right at the points I set it. The wrench was 25-30 years old when I did that so I have an idea it is still good since it is stored in a clean dry place on zero.

I'm with Crane Operator. We really need to know what size bolt and torques we are talking about.

in my opinion, 1/2 turn past recommended torque on any fastener is considerably overtorqued and may be at or past the fastener's elastic limit which is not good. also, consider the female threads which are likely close or at the failing point. nothing was mentioned about the grade of bolt or the thread pitch (fine or coarse). in a crank, i would assume UNF or metric fine thread. i would assume the crank is forged and a lot will depend on actual thread engagement. the weakest part of the bolt should be in the threaded area. a grade 8 bolt is likely stronger than the threads in the crank. were the threads lubed or threadlocker used during installation?

Want a quick check? Turn the bolt till just snug, then turn it one and half to two flats. Check it with the torque wrench for the prescribed torque. Your click type wrench will click every time if it is calibrated properly.

I just had my 3/4 drive MAC rebuilt. They checked the calibration on it after rebuilding the head. Right on the money. I should probably send my little Westward ones out for calibration. Had them close to 15 years.