box covers for flatness; re-surface them if necessary. After  installing the gaskets and covers, tighten the rocker-box cover  nuts to the specified torque. Always follow the recommended  safety procedures. The cold cylinder check determines the operating  characteristics of each cylinder of an air-cooled engine.  The tendency for any cylinder, or cylinders, to be cold,  or to be only slightly warm, indicates lack of combustion  or incomplete combustion within the cylinder. This must  be corrected if best operation and power conditions are to  be obtained. The cold cylinder check is made with a cold  cylinder indicator. Engine difficulties that can be analyzed by use of the cold  cylinder indicator are  [Figure 10-55] : In preparation for the cold cylinder check, head the aircraft  into the wind to minimize irregular cooling of the individual  cylinders and to ensure even propeller loading during  engine operation.  Operate the engine on its roughest magneto at a speed between  1,200 and 1,600 rpm until the cylinder head temperature  reading is stabilized. If engine roughness is encountered  at more than one speed, or if there is an indication that a  cylinder ceases operating at idle or higher speeds, run the  engine at each of these speeds, and perform a cold cylinder  check to pick out all the dead or intermittently operating  cylinders. When low power output or engine vibration is  encountered at speeds above 1,600 rpm when operating  with the ignition switch on both, run the engine at the speed  where the difficulty is encountered until the cylinder head  temperatures have stabilized. and proceed in numerical order around the engine, as rapidly  as possible. To obtain comparative temperature values, a firm  contact must be made at the same relative location on each  cylinder. Note any outstandingly low (cold) values. Compare  the temperature readings to determine which cylinders are  dead (cold cylinders) or are operating intermittently. Difficulties that may cause a cylinder to be inoperative  (dead) when isolated to one magneto, either the right or left  positions, are: When cylinder head temperatures have reached the stabilized  values, stop the engine by moving the mixture control to  the idle cutoff or full lean position. When the engine ceases  firing, turn off both ignition and master switches. Record the  cylinder head temperature reading registered on the flight  deck gauge. As soon as the propeller has ceased rotating,  apply the instrument to each cylinder head, and record the  relative temperature of each cylinder. Start with number one  10-44 1.  Defective spark plugs 2.  Incorrect valve clearances 3.  Leaking intake pipes 4.  Lack of compression 5.  Defective spark plug lead 6.  Defective fuel-injection nozzle  1.  Rough engine operation 2.  Excessive rpm drop during the ignition system check 3.  High manifold pressure for a given engine rpm during  the ground check when the propeller is in the full low- pitch position 4. Faulty mixture ratios caused by improper  valve clearance Figure 10-55.  Cold cylinder indicator.  Cold Cylinder Check OIL 5 4 300 200 0 100