Signs of Abuse The mad torquer strikes again.


torque wrench in-use At the back of old-time owner’s manuals there was always a table of fastener torques–so many foot-pounds for head bolts, so many for case bolts, and so on. Did anyone ever use that information? I have encountered veteran engines whose condition suggested they did not. A case in point was a clutch cover, retained by the usual 6mm Phillips-head screws. Each screw had been heavily overtorqued each time the case was replaced on the engine after clutch service. The solid aluminum of the case had squeezed out from under the screw-heads as if it were stiff butter, trapping some of the fasteners. This was completely unnecessary to making the cover gasket seal. The engineer who designed the case chose the number of fasteners and their size to be sufficient to the task. If more clamping force had been desired, that engineer would have chosen either more or bigger fasteners. So this was a case of an owner who couldn’t be bothered. Had this owner developed the ‘feel’ for 6mm screws that even moderately experienced mechanics have, that case cover would not have been mangled, and it would have sealed perfectly well. Very likely, the owner either used a hammer-driver to tighten those case screws, or an air wrench on a higher-than-necessary setting. Needless carelessness in either case. It all reminds me of the story told to me by a hot-rodder about a user of Summers Brothers high-strength axles who was breaking their wheel studs. The studs were made of high-specification material and the installation torque was clearly stated. Finally a manufacturer’s rep decided to make a customer call in case there were some obscure problem they should attend to. Upon request, the user produced his quite fancy clicker-type torque wrench, and showed a certificate stating that it had recently been calibrated. So the rep said, “Could you please show me just how you perform the tightening?” The user nodded and they went to a car with the axle shafts installed. With a wheel in place and nuts run down to contact, he torqued the fasteners in steps, then reset to the full installation torque. With a practiced movement, he swung the wrench until it clicked. And then he added an extra quarter-turn. “What’re you doing?” spluttered the rep, his voice rising in alarm. “You’ve grossly over-torqued it! That’s why you’re breaking studs!” The customer looked puzzled. “I do ‘em all that way. I don’t want ‘em to come loose, right?” Fastener torque specs exist to provide the necessary clamp load at a level of stress that the fastener’s material and design can reliably sustain.