Every Twenty Hours:
After every twenty hours of flight the valve gear should be disassembled and inspected as follows:
Including: Service Instruction No. 35, 36.
Cylinder Heads : -----------------------------
Turn the crankshaft until the valves of the No. 1 cylinder indicate that the piston is on top center at the beginning of the suction stroke. At this point both the valves will be open and the keyway in the shaft will be facing the No. 1 cylinder. If the propeller is mounted on the shaft one of the blades will be in the line of the keyway. Then turn the shaft through one complete revolution and set the clearances on the No. 1 cylinder:
Loosen the push rod housing clamping screw And back off on the adjusting nut until the push rod housing is free. With a set of thickness gages check the clearance under rear end of the rocker box. To this value add .005" and tighten up on the adjusting nut until the increased clearance is obtained. Then tighten up on the clamping screw. It is
essential that this be done when both the valves are closed to prevent errors caused by the forces set up when the valve is opening or closing.
Check the valve tappet clearances. Just before checking the clearance, the push rod end of each rocker arm should be tapped sharply with a hammer handle to make sure the roller is riding on the cam. The cam followers are fitted with very little clearance and are sometimes too tight to be moved easily with the fingers, necessitating this operation. It has been noted that many operators make curved feelers .040" thick for setting the tappet clearance.
The clearance for both tappets is .040". Loosen the clamping screw on the push rod end of the rocker arm and with a large screw driver turn down on the adjusting screw until the rocker roller touches the valve plug. Then back off on the adjusting screw until the arrow on top has passed eight divisions of the scale on the rocker arm (each division is equivalent to .005" clearance on the valve stem). Lock in place by tightening the clamping screw.
The cotter pins should be removed and the rocker arm pin nuts checked for tightness. This is very important as any looseness on the part of this nut permits the rocker arm pin, sleeve and thrust washers to turn and is apt to cause serious wear in these parts.
Grease the rocker arms.
Cylinder Heads : -----------------------------
Repeat on the rest of the cylinders, taking them in the firing order (1, 3, 5, 7, 9, 2, 4, 6, 8).
After the valve gear has been inspected, repaired and reassembled the following items should be checked:
- Are spark plug points clean and are gaps set at proper clearance.
- Are nuts on inlet pipe upper flanges tight?
- Are inlet pipe packing nuts tight?
- Are cylinder hold down nuts tight?
- Are fuel strainers clean?
- Are fuel lines and connections secure and free from leaks?
- Is lock on gasoline pump pressure adjusting screw secure?
- Drain the oil from the tanks and lines
- Remove the oil lines and flush the oil tank and lines with kerosene until perfectly clean.
- Inspect and clean all 3 oil strainers.
- Replace the lines and put two gallons of clean oil in the tank. Run the engine for twenty minutes and then drain out all the oil again. Replace the lines and fill the tank with 5 gallons of clean oil.
- See that hand crank starting turning gear is well lubricated.
- Are engine mounting bolts tight?
- Does each magneto get full advance when operated from cockpit?
- Are magneto breaker points clean and gaps set at .012"?
- Are magneto couplings in good condition?
- Put four drops of medium machine oil in rear magneto oil holes. Fill front holes.
- Are propeller hub lock nuts and propeller hub bolts tight?
Complete Overhaul
It is suggested that the compression be checked very
carefully on each cylinder. As soon as one is found to be low it should be removed, the valves tested for leakage and the piston rings checked for tension. The valves should be ground and the piston rings replaced when necessary. In this manner the engine can be kept up to power and speed. It is sometimes very difficult to distinguish between a valve which is leaking and one which is being held open by a bit of dirt or carbon on the seat. The only way to check this out is to run the engine for several minutes and then try the compression again.
Experience with "Whirlwind" engines in service has indicated that the length of the period between overhauls is limited by the tendency of the lubricating system to fill up with sludge. This is composed of gums formed in burning the lubricating oil, carbon, lint and substances taken into the engine through the carburetor or breathers.
After 200 hours of service the accumulation is likely to become severe enough to plug up one of the passages resulting in the seizure of the bearing whose oil supply is cut off. It is therefore recommended that "Whirlwind" engines be given a complete overhaul after every 200 hours of service.