Torque wrench using adapters?

[CopperNick]

+1 on what Hurst Olds stated. The physical condition of the fastener is just as important as is whether or not some type of lubricant was used on the fastener threads. MFGR's like ARP provide their own special lube for use with their fasteners so that the demanded torque value, when established using a torque wrench, will be correct.

Where things change is if you use an offset adapter instead of just an extension and 6 pt allen socket. For purposes of this discussion, torque adaptors are not those couplings that you use to change from one drive size to another. They are actually a specialty piece that allows you to have the driver or wrench out in the open while still being able to access the nut or bolt or screw that is otherwise somewhere where it can't be reached easily. Snap On is one example of a Mfgr that offers them, and the ones in my roller box are 3/8ths drive by 1/2 and 9/16ths by 12 pt hex ends. Crow foot wrenches are another example of this that gets uses when a gas or hydraulic fitting can't be accessed directly.

If the situation demands one of these be used with a torque wrench, be aware that it changes the final value of the torque that is delivered to the fastener. The dial or indicator on the wrench will display the desired value when the torque is applied, but the actual torque at the fastener is greater. Because of the use of the offset adaptor, the torque is no longer being applied in a straight line, What the offset adaptor does is to increase the leverage that the torque wrench is applying to the fitting or fastener. There are actually tables and formulas that can be used to calculate display vs actual and how much less torque needs to be applied by the wrench due to the greater leverage to get the correct amount. at the bolt.

I use both Snap On and Gray Tool torque wrenches and they came with instructions including how to calculate corrected torque value based on the length of the offset adaptor.
Might be a You-Hoo Video somewhere that explains it all in pictures


Nick

 

[64nailhead]

The extension creates an inaccurate torque if it twists.

In an extreme example, imagine torquing a bolt using an extension that is a spring that requires 100ft/lbs to twist, now use that spring (extension) to achieve a torque less than 100ft/lbs. On the other hand, if you have an extension that doesn't twist until above the desired torque, then it will be fine.

Another example that I'm confident many of has encountered, trying to remove a bellhousing bolt with every extension you own on an impact.

Another example - explain how does a torque stick work?

 

[Max Headroom]

Correct me if I am wrong but I think the video posted above is not accurate in all cases. It only applies to extensions which cannot recover from being twisted by rotational force, like an extension. For example: if it takes 100 ft/lbs of torque to permanently twist an extension and you apply 150 ft/lbs of torque to a bolt with that extension in place, all other things being equal, you will end up having applied 150 ft/lbs of torque to the bolt. (after the extension bends) When you are finished torquing the bolt the extension will remain bent.

On the other hand, if you use an Allen shaft that will begin to bend (twist) at a value less than the torque value required and will still have the ability to twist further past the required torque value, you will apply less torque to the bolt head than the wrench is set at. The difference is the amount of force required to keep the Allen shaft in torsional tension. When you take pressure off the torque wrench, the Allen shaft will return to its normal untwisted shape. In essence, the Allen shaft acts like a spring and requires a certain amount of force to hold it in its "bent" shape. That force is not applied to the bolt

If however, you twist the Allen shaft to permanent deformation (permanently bent) before reaching the desired torque, all of the force exerted will be transferred to the bolt head. (minus any lost to deflection from the axis of force applied) head. When you take the pressure off the wrench, the Allen shaft will remain twisted.

I could be wrong (ask my wife) but I don't think so.

 

[olds307 and 403]

Another thing is calibration of the torque wrench. I have one that reads 10 ft/lbs lower than actual torque. I torqued a rear main cap on my 403. I believe the spec is 110 but I found 120 somewhere. I set it to 120 ft/lbs and the cap broke. I was actually putting 130 ft/lbs. I tested it against two other torque wrenches it was off compared to them around 10 ft/lbs. I also broke a head bolt on a 350 using 7/16" head bolts with 1/2" 5A 307 heads. I thought washers will fill the gap. They did but obviously stretched and totally skewed the torque value. I think the wrench was showing 60 ft/lbs when it broke.

 

[64nailhead]

When you take pressure off the torque wrench, the Allen shaft will return to its normal untwisted shape. In essence, the Allen shaft acts like a spring and requires a certain amount of force to hold it in its "bent" shape. That force is not applied to the bolt

EXACTLY!!

This is why an extension can affect the torque. The extension is basically a spring. Stress vs. strain - if you have a couple hundred hours of time to kill, then learn what is occurring in the stress vs. strain relation. The relation explains in detail why a TTY bolt cannot be re-used it you want an accurate clamping force.

On the other hand, if you have an extension that requires more torque to twist than you are applying, then it will provide an accurate torque.

 

[64nailhead]

Another thing is calibration of the torque wrench. I have one that reads 10 ft/lbs lower than actual torque. I torqued a rear main cap on my 403. I believe the spec is 110 but I found 120 somewhere. I set it to 120 ft/lbs and the cap broke. I was actually putting 130 ft/lbs. I tested it against two other torque wrenches it was off compared to them around 10 ft/lbs. I also broke a head bolt on a 350 using 7/16" head bolts with 1/2" 5A 307 heads. I thought washers will fill the gap. They did but obviously stretched and totally skewed the torque value. I think the wrench was showing 60 ft/lbs when it broke.

FWIW, 2 years ago every Navistar, synonymous with 13 letter sh*t spreader, dealer was sent as an essential tool a torque wrench checking tool. In a nutshell, it measures the accuracy of your torque wrench and can be done in moments. If anyone is interested in watching one of these things function, then let me know and I'll send a video.

I recheck my crapsman wrench everytime I get into a motor. Checking the $50 wrench working on the $5K+ short block makes me much more comfortable and less anxious.

 

[superbon54]

EXACTLY!!

This is why an extension can affect the torque. The extension is basically a spring. Stress vs. strain - if you have a couple hundred hours of time to kill, then learn what is occurring in the stress vs. strain relation. The relation explains in detail why a TTY bolt cannot be re-used it you want an accurate clamping force.

On the other hand, if you have an extension that requires more torque to twist than you are applying, then it will provide an accurate torque.

Nope. 69hurstolds had it right a number of posts ago with Newton’s 3rd law. It doesn’t matter how large the extension is or how many you have daisy chained together. As long as nothing breaks and as long as the torque applied is on the same axis as the fastener, ALL the torque transfers to the fastener. If the torque applied is off axis, some of it is lost. You can draw a free body diagram and calculate the torque loss with some simple trigonometry. Extensions don’t work well with an impact because the force is in a constant transient (on-off-on-off) state and the “slop” takes up the instantaneous force.

 

[64nailhead]

Nope. 69hurstolds had it right a number of posts ago with Newton’s 3rd law. It doesn’t matter how large the extension is or how many you have daisy chained together. As long as nothing breaks and as long as the torque applied is on the same axis as the fastener, ALL the torque transfers to the fastener. If the torque applied is off axis, some of it is lost. You can draw a free body diagram and calculate the torque loss with some simple trigonometry. Extensions don’t work well with an impact because the force is in a constant transient (on-off-on-off) state and the “slop” takes up the instantaneous force.

I respectfully disagree, both of you are overlooking the differences between sliding and static friction. The spring example, or twisting extension exacerbates this relationship between the two.

 

[fleming442]

I thought the same. The video i posted changed my mind. Dude created every reasonable situation on a Snap On calibration machine with little to no changes. Of course, there's going to be some change, but, in the end, you end up splittin short'n' curlies- not enough to worry about. SEND IT!!!!

 

[superbon54]

I respectfully disagree, both of you are overlooking the differences between sliding and static friction. The spring example, or twisting extension exacerbates this relationship between the two.

Technically we’re both right, but we can agree to disagree. Not trying to pick a fight, so don’t take my debate as anything other than that.

If you’re torquing a bolt properly, the only kinetic friction is that if the threads and head of the fastener to mating components, which is exactly what we’re measuring with the torque wrench. The friction indirectly translates to a clamp load which is based on a number of geometric and physical factors. Any friction within the tool is eliminated in a steady state. If you’re torquing too fast and impact loading the tool there could be additional friction, but you might as well just burn the fastener down with an impact at that point. I’ve worked on some high torque, high precision industrial applications where fasteners must be torqued below a maximum angular velocity (how fast the tool is spinning) to be within spec. The reason is to avoid the instantaneous loading/unloading of the “tool” and affecting the true fastener torque value. In our vehicular applications, that flex movement is far within the tolerance of the wrench calibration and we’re just splitting short hairs.