Hall-Scott Lubrication System
The oiling system of the Hall-Scott type A-5 125 horse-power engine is clearly shown at Fig. 77. It is completely described in the instruction book issued by the company from which the following extracts are reproduced by permission. Crank-shaft, connecting rods and all other parts within the crank-case and cylinders are lubricated directly or indirectly by a force-feed oiling system. The cylinder walls and wrist pins are lubricated by oil spray thrown from the lower end of connecting rod bearings. This system is used only upon A-5 engines. Upon A-7a and A-5a engines a small tube supplies oil from connecting rod bearing directly upon the wrist pin. The oil is drawn from the strainer located at the lowest portion of the lower crank-case, forced around the main intake manifold oil jacket. From here it is circulated to the main distributing pipe located along the lower left hand side of upper crank-case. The oil is then forced directly to the lower side of crank-shaft, through holes drilled in each main bearing cup. Leakage from these main bearings is caught in scuppers placed upon the cheeks of the crank-shafts furnishing oil under pressure to the connecting rod bearings. A-7a and A-5a engines have small tubes leading from these bearings which convey the oil under pressure to the wrist pins.
A bi-pass located at the front end of the distributing oil pipe can be regulated to lessen or raise the pressure. By screwing the valve in, the pressure will raise and more oil will be forced to the bearings. By unscrewing, pressure is reduced and less oil is fed. A-7a and A-5a engines have oil relief valves located just off of the main oil pump in the lower crank-case. This regulates the pressure at all times so that in cold weather there will be no danger of bursting oil pipes due to excessive pressure. If it is found the oil pressure is not maintained at a high enough level, inspect this valve. A stronger spring will not allow the oil to bi-pass so freely, and consequently the pressure will be raised; a weaker spring will bi-pass more oil and reduce the oil pressure materially. Independent of the above-mentioned system, a small, directly driven rotary oiler feeds oil to the base of each individual cylinder. The supply of oil is furnished by the main oil pump located in the lower crank-case. A small sight-feed regulator is furnished to control the supply of oil from this oiler. This instrument should be placed higher than the auxiliary oil distributor itself to enable the oil to drain by gravity feed to the oiler. If there is no available place with the necessary height in the front seat of plane, connect it directly to the intake L fitting on the oiler in an upright position. It should be regulated with full open throttle to maintain an oil level in the glass, approximately half way.
An oil pressure gauge is provided. This should be run to the pilot’s instrument board. The gauge registers the oil pressure upon the bearings, also determining its circulation. Strict watch should be maintained of this instrument by pilot, and if for any reason its hand should drop to 0 the motor should be immediately stopped and the trouble found before restarting engine. Care should be taken that the oil does not work up into the gauge, as it will prevent the correct gauge registering of oil pressure. The oil pressure will vary according to weather conditions and viscosity of oil used. In normal weather, with the engine properly warmed up, the pressure will register on the oil gauge from 5 to 10 pounds when the engine is turning from 1,275 to 1,300 r. p. m. This does not apply to all aviation engines, however, as the proper pressure advised for the Curtiss OX-2 motor is from 40 to 55 pounds at the gauge.
The oil sump plug is located at the lowest point of the lower crank-case. This is a combination dirt, water and sediment trap. It is easily removed by unscrewing. Oil is furnished mechanically to the cam-shaft housing under pressure through a small tube leading from the main distributing pipe at the propeller end of engine directly into the end of cam-shaft housing. The opposite end of this housing is amply relieved to allow the oil to rapidly flow down upon cam-shaft, magneto, pinion-shaft, and crank-shaft gears, after which it returns to lower crank-case. An outside overflow pipe is also provided to carry away the surplus oil.