USE A TORQUE WRENCH

Press, Volume CIX, Issue 32018, 19 June 1969, Page 14

USE A TORQUE WRENCH

TN the early days of motoring all one needed for most repairs was a pair of pliers, an adjustable wrench, a screwdriver; and a coin. This was the case until nearly 1935, when Henry Ford decided to build a V 8 engine which needed closer-fitting parts. Many changes have taken place since breaker-points were gapped with a coin, and con-rod and bearing caps were tightened by feel. It was possible in the early days because moving parts had a low tolerance fit. But if the average new 1922 or 1923 model was called on to run at the speeds and over the distances that are required of the modem car, it would not be long before con. rod bearings hammered out, valves failed, or pistons were driven down into the crankcase. GREAT FORCE. Few amateur mechanics, and not all .professionals, rea-

Use the tremendous torque that can be appUed with even a small spanner. If one is foo|ish enough to lengthen the handle of a wrench with a section of pipe, the force applied to the nut or bolt can be extremely high. Because of this, home mechanics often succeed in shearing bolts and studs, or in overtightening bolts so badly that they actually stretch. Some mechanics say that amateurs cause as much damage to their cars by overtightening nuts and bolts as by any other fault.

ESSENTIAL Today it is no longer sufficient to tighten nuts and bolts by guesswork, and this is why a torque wrench is an essential tool for all but minor jobs. When car manufacturers began designing for high horsepower, tolerances between moving parts became much less. This was especially so as regards the clearance between the con-rod bearings and the crankshaft, and between the crankshaft and the main bearings. These are the parts which must withstand the tremendous pressures developed in the combustion chambers. The precise clearances necessary require the use of a torque wrench. Cylinder-heads are another example. If they are not tightened down evenly, the gasket will blow, and the cy-

Under head may be damaged. Manuals give the torque i which must be applied for 1 the correct tightness. Each i bolt should have at least three I tightenings before this final I figure is reached, about 70 < per cent of the full figure i being applied on the first i tightening. I

When using a torque wrench, always hold it by the handle provided. On some wrenches holding the tool at the wrong point will give a false reading. Pressure should always be applied at 90 degress to the wrench handle, and wrenches should always be stored in a safe, dry place.