SUMMER 2013 | MARINE TECHNICIAN TODAY
17
A
ny technician that has been in the marine business for
any length of time most likely uses a torque wrench
several times a week, or even more. With that said, two
of the main reasons to use a torque wrench are to achieve
proper clamping forces on a part and to have even torque values on the
fasteners being installed. Torque is expressed in units of measurement.
The most common units of measurements are: In. lbs. = inch pounds;
in. ozs. = inch ounces; ft. lbs. = foot pounds; Nm. = newton meters;
cNm = centi-newton meters.
Torque versus clamping force, what is the difference? Only a small part
of the torque applied to a fastener contributes to the clamping force.
Total applied torque is used to overcome the friction under the fastener
head or between the nut and washer plus the friction in the thread
engagement. The following torque percentages as distributed to the
fastener and part are approximately: Head friction 45% - 55%, thread
friction 35% - 45%, and clamping force at about 10%.
Torque wrenches shouldn’t be viewed as just another wrench in the tool
box. They are precession measuring tools and need to be appropriately
cared for. A professional engine builder looks at them as one of the
most important tools in their tool box, and would never store them in
the bottom of their tool box under a pile of other tools. Here are some
torque wrench do’s and don’ts for proper operation:
Here are important Don’ts:
1. Don’t apply torque using a pushing motion.
2. Don’t use a cheater bar attached to your torque wrench. You
will never achieve proper torque values, plus it can damage the
torque wrench.
3. Don’t use rusted, dirty, cracked, worn or wet sockets attached
to your torque wrench for applying torque.
4. Don’t use rusted, dirty, stretched, or worn fasteners.
Proper torque just can’t be achieved with inferior parts.
5. Don’t use your torque wrench to break fasteners loose.
6. Don’t torque fasteners in a fast ratcheting movement.
7. Don’t store your torque wrench in humid conditions or with
weighted objects on top of it.
8. Don’t drop your torque wrench, if you do it would be wise to
have it recalibrated.
Here are important Do’s:
1. Always return your click type torque wrench to the lowest
setting after every use. Leaving your torque wrench with a
set value will weaken the spring inside and eventually cause
incorrect achieved torque values.
Torque
Wrenches
THE
PERFORMANCE
CORNER
Part One
By JohnMosetti
.
Always grasp the handle
firmly in the center of the
grip handle while applying
torque and try to use this
position for every fastener.
