Keeping It All Together

Torque Wrenches- How Good Are They?

By Joseph C. Dille
BMWMOA #24754

Part 3 of 3

It is important to have a reliable, accurate torque wrench to properly tighten fasteners to specification. A torque wrench is probably be one of the most expensive hand tools in your collection. In this, the final installment, I explain the differences between the two common types of torque wrenches and explain how to use them. I also share data I obtained by testing a bunch of wrenches.

There are two common types of torque wrenches for home shop use; the "beam" type and the "clicker" type. The beam type torque wrench is shown in Figure 1c and is the least expensive torque wrench. The beam wrench works by the beam bending in response to the torque applied as shown in Figure 2c. This type is very simple, reliable, and accurate, and there is little that can go wrong with it when used properly. When tightening a bolt, make sure to only apply force in the center of the handle. This allows the beam to bend in the manner it was designed to indicate the correct torque. Do not over torque the wrench or the beam may bend permanently. Do not drop the wrench because rough handling can bend the pointer arm or pointer. If the pointer is bent, it can be bent back to the center without affecting accuracy. If the beam is bent it cannot be bent back.

Parts of A Beam Torque Wrench
Figure 1c, Parts of A Beam Torque Wrench

Beam Torque Wrench Operation
Figure 2c, Beam Torque Wrench Operation

Figure 3c shows the clicker torque wrench, which is sometimes called a digital wrench. A clicker torque wrench works by preloading a "snap" mechanism with a spring to release at a specified torque. When the mechanism releases the ratchet head it makes a "click" noise as shown in Figure 4c. The torque is set by rotating the handle until the desired torque is shown in the window. Older clicker wrenches have a micrometer style scale along the handle instead of a window. The clicker wrench is much easier to use because it is easy to set the desired torque and just pull until you feel the click. The ratchet head also makes it easy to use in confined spaces. It is good practice to set a clicker wrench to its lowest setting before putting it away to prevent the spring from taking a set. Avoid rough handling and dropping because it can damage the mechanism. Do not use the torque wrench to loosen tight fasteners since this may damage the calibration.

Parts of A Clicker Torque Wrench
Figure 3c, Parts of A Clicker Torque Wrench

Parts of A Beam Torque Wrench
Figure 4c, Clicker Torque Wrench Operation

I always wondered about the accuracy of torque wrenches, so I made my own torque wrench tester. The tester consisted of a lever arm that lifted a series of weights off the floor. The torque tester is shown in operation in Figure 5c. By changing the position of the weights on the lever arm and changing the weights, I could obtain torques from 3 to 105 ft-lb. The weights were barbell weights that I determined the exact weight using a digital shipping scale. I then calibrated the lever arm by using a precision electronic torque wrench and then back calculated the lengths using my known weights. A known torque exists when the arm is horizontal and the weights jar lifted off the floor. I made a table of lever arm lengths and weight combinations so I could determine the applied torque in any situation. I estimate the accuracy of my home-built instrument to be +/-3% of the calculated torque.

Torque Tester
Torque Tester
Torque Tester in Operation
Joey Dille Demonstrating the Torque Tester

Figure 5c

Using the torque tester is straight forward. The pivot tube is placed in a vise and the desired weight is placed on the holder. The lifting chain/cable is then adjusted so the lever arm is parallel to the floor and located at the desired length per the torque table. The torque wrench is then inserted into the tester so it is approximately even with the lever arm. For beam wrenches, the wrench is rotated until the weights come off the floor and the indicated torque and applied torque are recorded. For clicker wrenches, the procedure is a little different. The wrench is set for torque slightly below the calculated applied torque. The wrench is then inserted in the tester and rotated slowly until it clicks. The wrench is set for the next higher torque increment and tried again. Successively higher torque settings are tried until the weights can be lifted from the floor without the wrench clicking. The highest setting where the wrench still clicked was recorded along with the applied torque. I learned that it was important to rotate the wrench slowly to avoid premature clicking caused by the inertia of the weights.

Once complete, I decided to use my new toy to check a bunch of torque wrenches to see how good they really were. I asked my friends in the Mac-Pac* to bring their torque wrenches to one of our wrench sessions at Bruceís garage. I was able to test a total of 13 wrenches, 3 beam, and 10 clickers. The results of my testing is shown in Table 1c and Figures 6c and 7c. I found the clickers to be much more repeatable than I expected. The beam type and clickers were both fairly accurate and linear over their range. The bottom line is torque wrenches, even inexpensive ones, were quite good.

Owner Size Type Range
ft-lb
Maximum Error Average Error
ft-lb % ft-lb %
Joe 3/8 Clicker 5-75 -7.3 -12.3% -5.0 -11.0%
Joe 3/8 Beam 2-50 1.3 0.3% 0.6 0.2%
Roger 3/8 Clicker 2-21 -1.6 -13.9% -0.8 -8.6%
Bruce 3/8 Clicker 2-21 1.0 5.3% 0.8 1.7%
Mike D. 3/8 Clicker 10-80 1.2 0.6% 0.2 0.1%
Wayne 3/8 Clicker 10-75 -2.8 -6.8% -1.6 -4.0%
Joe (new) 1/2 Clicker 10-150 -4.3 -4.7% -1.7 -2.4%
Joe (old) 1/2 Clicker 10-150 4.7 -10.7% 0.2 -0.6%
John 1/2 Clicker 10-150 -3.3 20.0% -1.0 1.1%
Mike D. 1/2 Beam 5-150 7.8 28.1% 4.9 12.7%
Ron 1/2 Beam 5-150 -4.3 -6.8% -2.5 -4.3%
Bruce 1/2 Clicker 25-250 -1.8 -3.4% -0.8 -1.3%
Mike B. 1/2 Clicker 10-150 2.7 3.9% 1.2 2.0%

Calibration Results for 3/8
Figure 6c

Calibration Results for 1/2
Figure 7c

If you wonder about the accuracy of your wrenches, you can get them calibrated by a Snap-On tool dealer or a local metrology lab. Griotís Garage can also calibrate torque wrenches on a mail order basis for $25 plus shipping.

Torque Wrenches and Accessories

From time to time people have asked me if it is OK to use an extension with a torque wrench. The answer is yes. Using an extension or reducer with a torque wrench does not affect the accuracy. Others have asked if it is OK to use a universal joint with a torque wrench. The answer is NO. Universal joints change the torque as the drive angle increases. I checked this out with my torque tester. The results are shown in Figure 8c. Donít use universal joints with torque wrenches.

Effect of Universal Joint on Torque Reaction
Figure 8c

Torque extensions are sometimes required to tighten fasteners in locations where the torque wrench will not fit such as the drive shaft flange on older airheads. Figure 9c shows the extension I made for this purpose. To work correctly, one must understand how the position of the extension affects the torque as shown in Figure 10c. There is a formula for relating actual bolt torque to the wrench torque based on the length of the wrench and extension and the angle between the two. It is best to keep the two at right angles so the torque will be the same.

Home-Made Torque Wrench Extension
Figure 9c, Home-Made Torque Wrench Extension

Proper use of Torque Wrench with Extension
Figure 10c, Proper use of Torque Wrench with Extension

I wish to thank fellow BMW riders:

for their help editing the article and providing encouragement. I hope this article has removed some of the mystery from the little things that keep our bikes together. I will close with a list of useful fastener-related references.

Fastener References:

Mr. Metric Inc.
960 NORTH 10TH STREET
SAN JOSE, CA 95112
(800) 944-1897
Stainless and Plain Steel Fasteners
Nice Catalog
http://www.fastenerweb.com/mrmetric
Maryland Metrics
P.O. Box 261
Owings Mills MD 21117
(800) 638-1830
Stainless and Plain Steel Fasteners
Great technical section on web site
http://mdmetric.com/
Gardner-Wescott Co.
10110 Six Mile Road
Northville MI 48167
1-800-897-5025
Stainless and Plain Steel Fasteners
No minimum order
http://www.gardner-westcott.com/index.html
Barnhill Bolt
2500 Princeton NE
Albuquerque, NM 87107
(505) 884-1808
Stainless and Plain Steel Fasteners
Good online FAQ
http://www.barnhillbolt.com
Metric & Multistandard Corp.
120 Old Saw Mill River Rd
Hawthorne NY 10532
1-888-966-MMCC
Stainless, Plain Steel Fasteners and Tools
Good catalog and technical information
http://www.metricmcc.com
Internet BMW Riders
Links to Many Fastener Suppliers
http://www.ibmwr.org/faq-files/addresses.html
Rocky Point Cycle
2509 Linebaugh Rd
Xenia OH 45358-9512
937-376-9792
Stainless Fasteners and Parts
Good stainless selection
http://www.rockypointcycle.com
Moto-Bins Ltd
16 Surfleet Road
Surfleet,Spalding
Lincolnshire PE11 4AG UK
+44 (0)1775 680881
Stainless Fasteners and Parts
Rare stainless bits
http://www.motobins.co.uk/indexie.html
Emhart Fastening Teknologies
510 River Road
Shelton, CT 06484 USA
203-924-9341
HeliCoil Thread repair kits
http://www.emhart.com/products/helicoil.html
Loctite Corp.
10 Columbus Boulevard
Hartford Square North
Hartford, CT 06106
860.520.5000
Thread locker and thread repair components
http://www.loctite.com
Snap-On
2801 80th Street
PO Box 1410
Kenosha, Wisconsin 53141-1410
1-800-TOOLS-4-U (1-800-866-5748) Tools and Torque wrench calibrations
http://www.snapon.com
Airheads Beemer Club
Great Article on Heli Coilstm
http://www.airheads.org/contrib/helicoilprimer.html
Griotís Garage
3500-A 20th St. E.
Tacoma WA 98424 800-345-5789
Tools and Torque wrench calibrations
http://www.griotsgarage.com
WTI Fasteners LTD
British manufacturers of Helical wire thread inserts
www.wti-fasteners.co.uk/frames.htm
Alfa Romeo Owners of Oregon
International Fastener Guide :-)
www.alfaclub.org/techstff/us.htm
The Bolt Depot
286 Bridge Street
North Weymouth, MA 02191
1-866-337-9888
Fasteners and lots of good tech info
http://www.boltdepot.com/fastener-information/Default.aspx
Tegger's Torque Wrench FAQ
A great exploded view and explination of how a clicker wrench works.
http://www.tegger.com/hondafaq/torque_wrench/index.html
Stainless Fasteners Handbook
A design guide by the Stainless Steel Industry of North America. This is a great compilation of information. The technical information is spot on, but the material comparisons are a bit biased. Read with care.
http://www.ssina.com/view_a_file/fasteners.pdf
Flexible Assembly Systems Inc.
8451 Miralani Drive, Suite N
San Diego, CA 92126
(800) 696-7614
High end industrial torque wrenches, calibration services and FAQs
http://www.flexibleassembly.com/
Thanks for visiting!

*The Mac-Pac is a group of BMW riders in Southeastern Pennsylvania who communicate via an e-mail list server. Details at http://www.mac-pac.org


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