The advent of the torque wrench nearly a century ago brought forth a newfound accuracy to the mechanical industry. Gone were the days of guesstimating only to sheer off a bolt head or under-tightening a nut to the point it came loose during a ride. But in reality do we really need to shell out big bucks for a torque wrench, or can we get close enough to the manual’s specs with our own muscle? Engine components and other tight-tolerance parts need to be torqued to spec since not doing so can result in catastrophic failure. But axle nuts and caliper bolts also require a certain pressure.
As a general rule of thumb older torque wrenches are considered accurate if they’re within four percent of spec (high or low) and newer ones narrow the scope to three percent. Rumor has it that some torque wrenches aren’t accurate from the factory while others grow more unreliable with use. A human arm and years of experience only get more accurate, but can that unscientific practice come within the accepted tolerances of torque wrench standards?
The Test: We hit the garage with several torque wrenches in hand and chose the one that was the most consistent after three attempts at tightening a nut or bolt from finger tight to torqued. We opted for the three most commonly over-torqued parts on a bike: rear axle nut, front axle pinch bolt and front brake caliper bolt. After sourcing recommended torque specs from several shop manuals we found an average and laid into the bike with a torque wrench before letting our seasoned shop mechanic loose for three tries using feel.
|The Results:|| |
|Rear Axle Nut ||Front axle pinch bolt||Front brake caliper bolt|
|(70 Ft-Lbs)||(12 Ft-Lbs)||(18 Ft-Lbs)|
|1) 65||1) 17||1) 22|
|2) 77||2) 15||2) 24|
|3) 92||3) 92||3) 14|
Torque specs aren't vague and open for interpretation like the price of a used bike on Craigslist. They've been put in place to maintain your motorcycle's efficiency and safety, and to ignore them and just tighten at will is plain foolish. Our experienced mechanic wasn't consistent enough to eliminate the need for a torque wrench, and if you think your arm can get the torque load "close enough" you're making a big mistake. Not only can bolts snap if over-tightened but they can even pull the threads loose, and retapping something sensitive to contamination such as brake caliper isn't a pretty job. Under-tighten and well, the bolt falls out. Save the potential for disaster and invest in a torque wrench.