Allen screws in the hub of the hook and lift the hook off the hook shaft. To remove the bobbin case from the hook assembly, loosen the hook gib screws, lift off the gib, and then lift out the bobbin case. Removing the Arm Shaft Connection Belt When the arm shaft connection belt is disconnected for any reason, the machine will be completely out of time. Therefore, the needle should be removed before removing the belt to prevent damage. To remove the belt, slide it off the lower belt pulley, loosen the screws in the machine pulley, and remove the pulley and ball bearing, which come out through the end of the arm. Replace the belt by reversing this procedure. Remove the end play from the shaft by lightly setting the setscrews and tapping the balance wheel into position with the palm of the hand and then securely setting the setscrews. Place the belt over the upper belt pulley and line up the timing marks on the lower belt pulley and on the bed of the machine. While holding the lower belt pulley in position, turn the balance wheel toward the operator’s position until the thread take-up lever is at its highest position, then slide the belt onto the lower belt pulley. The arm shaft connection belt and the lower belt pulley are illustrated with the safety clutch in figure 9-32. CAUTION DO NOT TAMPER WITH THE SAFETY CLUTCH. ITS TORQUE IS PRESET AT THE FACTORY. Lubrication The hook saddle is equipped with an oil reservoir (fig. 9-36), which contains oil to be pumped to the bobbin case raceway. The flow of this oil is controlled by a control valve screw located just aft of the bobbin case opener in the hook saddle. For more oil, turn the valve screw clockwise; counterclockwise for less oil. CAUTION DO NOT ADJUST FLOW OF OIL WITHOUT FIRST LOOSENING THE LOCKING SCREW LOCATED ON THE SIDE OF THE HOOK SADDLE JUST ABOVE THE CAM SHAFT GEAR. AFTER ADJUSTING THE CONTROL VALVE SCREW FOR PROPER FLOW, RETIGHTEN THE LOCKING SCREW. SINGER SEWING MACHINE 143 W 2 AND 3 This type of machine is not as common as those previously described, but it has unlimited uses in the repair and maintenance of parachutes and survival equipment. The 143 W 2 is a high-speed sewing machine that has an aluminum alloy vibrating needle bar frame and a rotary hook. It is intended for overseaming and zigzag stitching on fine and general fabrics and lightweight leather. It has ball bearings on the rear end of the arm shaft and hook driving shaft. The needle bar has a maximum throw of 3/16 inch, vibrating both sides of a centerline. The 143 W 3 sewing machine is similar to the 143 W 2 except that the needle has a maximum throw of 5/16 inch. The maximum speed recommended for machine 143 W 2 is 3,500 stitches per minute, and for machine 143 W 3, 3,000 stitches per minute, the speeds depending on the material being sewn. Needle and Thread The needles for sewing machines are the 143 W 2 and 143 W 3 of class and variety 135 x 7; the sizes from 7 to 24. Left twist thread should be used on these machines. To make a smooth even stitch with the sewing machine, use good, firmly twisted and smoothly finished thread. The thread should pass freely through the eye of the needle. Setting the Needle Push the needle up in the needle bar as far as it will go, with the LONG THREAD GROOVE TO THE FRONT, and secure it firmly with the setscrew. It may be necessary to turn the needle slightly to the right or left for some threads if stitches are missed. 9-30