Piston, 34 Piston pin, 34 Piston rings, 37 Piston rings; care of, 228 Plate clutch, 146 Poles of magnet, 106 Power diagram, 21 Power production, 12 Power stroke, 19 Preignition, 56, 83, 104 Priming the engine, 214 Pump feed carburetor, 80 Push rod, 42 Push rod adjustment, 234 Radiator, 48 Retard of ignition; theory of, 19 Rich mixture, 55 Rocker arm, 42 Safety spark gap, 127 Shuttle armature, 107 Sliding change speed gear, 154 Spark coil; principle of, 133 Spark coil; vibrator, 138 Spark coil; windings of, 134 Spark plug, 140 Spark plug gap, 226 Spark plugs; trouble with, 225 Splash oiling system, 184 Spray nozzle, 57 Spring support, 173 Starter; impulse, 128 Starting in cold weather, 207 Starting the engine; theory of, 13 Steering gear; purpose of, 7 Steering; instruction in, 205 Storing a tractor, 210 Straining the fuel, 89 Strangler, 69 Tappet, 42 Tappet adjustment, 234 Temperature; effect of changes on mixture, 66 Testing for magneto trouble, 224 Testing the compression, 227 Theory of gas engine, 9 Thermo-syphon cooling system, 48 Thin mixture, 54 Throttle, 68 Throws of crank shaft, 30 Timer; magneto, 110, 121, 122 Timing a magneto, 223 Timing the valves, 237 Tractor; caring for in cold weather, 207 Tractor; difficulties in oiling, 178 Tractor driving, 205 Tractor; handling a new, 201 Tractor inspection, 203 Tractors and automobiles compared, 1 Tractor; storing, 210 Tractor types, 167 Transmission; parts of, 143 Trouble; causes of, 259 Trouble; locating, 246 Valve; exhaust, 38 Valve grinding, 229 Valve; inlet, 38 Valve mechanism, 42 Valve operation, 39 Valve seat; redressing, 234 Valve timing, 237 Vertical engine, 25 Vibrator coil, 138 Viscosity of oil, 182 Washer; air, 91 Water added to mixture, 58, 83, 219 Water jackets, 48 Windings; Bosch magneto, 110 Windings of spark coil, 134 Worm drive, 166 Wrist pin, 34