Tools & Fabrication - Torque Wrench Question

Guys I have a question about using a torque wrench. Okay for example, I torque a bolt down to 25 ft/lbs, and click, I hear my torque wrench click at 25. I once again go back to check the torque on the bolt and the bolt spins a little bit more before reaching 25 ft/lbs again, Why does this happen? Bad torque wrench?

i notice the same thing, you feel it more if you turn it slower the second time, no clue

So its normal?

try torqueing it slow the first time. what brand wrench your have? i have a snap on techwrench and it does not do that, i always torque slowly, and evenly

You might take a read through the ARP fastener catalog if you are really interested in the why, but here is a quick excerpt:

There are a number of things to consider when using a torque
wrench. The “friction factor” changes from one cycle to the next.
That is, friction is at its highest value when the fastener is first
tightened. Each subsequent time the fastener is torqued and loosened,
the amount of friction lessens. Eventually the friction levels
out and becomes fairly consistent for all following repetitions.

Three basic elements that contribute to the friction factor:

1. Most importantly -The fastener assembly lubricant
2. The condition of the receiving threads
3. The surface finish of the fastener

Because of these variables, a phenomenon known as “preload
scatter” or preload error occurs. This is basically the difference
between the amount of preload achieved on the first installation
of the fastener and the amount of preload achieved on subsequent
torque/loosen/re-torque cycles. It’s not uncommon to see “preload
scatter” in the range of 4,000-8,000 pounds between the first and
tenth pull on a new fastener depending on the lubricant used.

One of the car shows the other week had a torque rig setup using different fastener lube. The ARP stuff was the only one that allowed the bolt to achieve the correct torque the first time. It's all I use then torquing a fastener down unless it calls for specific sealing procedures.

I wouldn't suspect the wrench first, like the great post above noted, there are many variables to take into consideration and any of them can heavily impact the final torque.

Great topic.

yea normally using any type of lubricant requires a bit more torque, but as long as you torque closer to the highest specified torque, it should be fine

yea normally using any type of lubricant requires a bit more torque, but as long as you torque closer to the highest specified torque, it should be fine

If you use the proper lubricant on the threads, it should require LESS torque to get the proper amount of preload in the fastener. Torquing something dry will require more torque because you are trying to overcome the metal on metal contact that is created by the male/female threads being jammed together.

its normal... i build T-58's (helicopter engines) and torque is a big thing when building them... this happens alot. even when using the proper lubricants, plastiseal, or antiseize.
what we do is torque wait 5 mins. then re-torque (if the bolt moved, wait another 5 mins and re-torque we do this process until the bolt no longer moves)

Completely normal. I always use a similar procedure as above. I torque all fasteners in sequence then repeat until I can apply the correct torque without movement. I don't wait 5 minutes between passes, but nobody's flying anything of mine...

Also as noted above- proper lubricant

Guys I have a question about using a torque wrench. Okay for example, I torque a bolt down to 25 ft/lbs, and click, I hear my torque wrench click at 25. I once again go back to check the torque on the bolt and the bolt spins a little bit more before reaching 25 ft/lbs again, Why does this happen? Bad torque wrench?

A couple of things are going on. one I alway like to have my tq wrench checked every year, it should always always be stored at 0 or below, and should not sit over night at any reading, also when you pull on the wrench you need to pull slow and steady, it is like lifting weights, you can fool the wrench by pulling fast. next is the style of lube if you use a good lube like arp moly that will make a difference in the reading.