One of the things I do for a living is calibrate torque wrenches. These devices are used in so many industries that it is almost unbelievable, every faction of our lives. What else is also unbelievable is how poorly treated many are, especially considering that they provide the most important function in all mechanical things: Tell if the bolts are tight!
After calibrating and repairing wrenches, I honestly feel that many of the unexplained failures of engines I have been around have been because of the bolts not being correct, even though it was torqued.
Wrenches have a few types based upon standards.
- Type 1: Bending bar style, torque watches, dial type indicator
- Type 2: Click and release type
- Type 3: Screwdriver style
- Electronic ones, but at $200-$400 most people can’t afford them.
Now, the following is my own opinion, and if you want to discuss it further, open a thread,
Electronic ones that I have calibrated are by far the most accurate and repeatable, both of which are very important in a wrench. Clockwise and counterclockwise are independently adjustable (very good function) Now the down side is they take batteries, most are plastic and don’t take drops very good, and the long term stability of their accuracy and repeatability over 2-10 years is still unknown.
Type 1 wrenches are the second best in accuracy and repeatability. They will take abuse in adverse conditions very well, most likely are superior to all other styles in these conditions. A very low percentage of these style need to be adjusted upon annual recalibration, and a few show signs of direction memory, which comes from using a wrench more in one direction than the other, and it, too is adjustable independently for both directions.
Type 2 wrenches are probably the most used everywhere and the worst of the 3 types of wrenches capable of torque in the 50-250 ft. lb. range. The principle it that a pair of flat anvils squeeze a small block inside the body of the wrench. One anvil is on the end of a long spring that floats inside the body, and screwing the handle in tightens the spring. There is the ratchet head on one end, and the anvil on the other end inner arm and it pivots on the pin in the body. The click you hear is the little block rolling up on its side when the torque force exceeds the spring force. Clear enough, right…lol
So you when you have a block that rolls up it on its edge everytime its clicked is prone to: edge wear, dirt, rust and grease fouling the block in either not rolling up (too much torque), debris under the block (too little torque), block rusted solid to the anvils, and rust filling the spring and causing WAY TOO much torque at the full scale of the wrench.
This is why any Type 2 torque wrench used needs to be checked often, preferably by someone who knows what they are doing. Here are some good tips for their use, along with most other torque wrench styles.
- Warm them up by clicking them first, before you start to torque stuff. 3 times at 60% of its full scale (highest wrench will go) and once before you go for your bolts.
- Always unscrew it when not in use, but DO NOT go below the lowest setting, even if there is more travel in the handle. Unscrewing further can drop the block out of place or cause your anvils to turn slightly causing erratic readings.
- Treat them like they are glass, because any treatment that would break a beer bottle can effect the wrench.
- Check and/or replace them often.
You can check you own wrenches various ways. The easiest is using a Type 1 to check a Type 2. A female drive to drive to put them together, secure the handle of the type 1 safely and solidly and pull the type 2 against it, noting the peak reading (many have a dial Type 1’s have a peak hold needle along with the readout needle). So there you go, your own calibration check.
What to do if they Don’t match! Now we have 2 readings, one the peak of the Type 1, and the Type 2’s setting, we will call this a click. Many clicks should be taken using the method above and in the same manner as the wrench is used in real life will be used.
If you torque a few bolts a year, a round of 6-10 clicks is probably fine. If you build engines on the weekends, you need a whole lot more clicks, and on a regular basis. If you trust your testing, then you can make correct tables for your wrenches. A wrench must repeat well if it is used for long sequences. Remember accuracy is hitting the target’s bulls-eye, and repeatability is how wide your spread of pattern is. A Wrench with a Wide Scatter is just a ratchet, Not a Torque Wrench!