The seven-bearing crank-shaft is finished all over in a beautiful manner, and the shaft out of the particular motor we have shows no signs of wear whatever. The crank-pins are 55 mm. in diameter and 69 mm. long. Through both the crank-pin and main bearings there is drilled a 28 mm. hole, and the crank cheeks are plugged with solder. The crank cheeks are also built to convey the lubricant to the crank-pins. At the fore end of the crank cheek there is pressed on a spur driving gear. There is screwed on to the front end of the shaft a piece which forms a bevel water pump driving gear and the starting dog. At the rear end of the shaft very close to the propeller hub mounting there is a double thrust bearing to take the propeller thrust.
Long, shouldered studs are screwed into the top half of the crank-case portion of the case and pass clean through the bottom half of the case. The case is very stiff and well ribbed. The three center bearing diaphragms have double walls. The center one serves as a duct through which water pipe passes, and those on either side of the center form the carburetor intake air passages and are enlarged in section at one side to take the carburetor barrel throttle.
The pistons are of cast iron and carry three concentric rings 1⁄4 inch wide on their upper end, which are pinned at the joint. The top of the piston forms the frustum of the cone and the pistons are 110 mm. in length. The lower portion of the skirt is machined inside and has a wall thickness of 1 mm. Riveted to the piston head is a conical diaphragm which contacts with the piston pin when in place and serves to carry the heat off the center of the piston.
The oil pump assembly comprises a pair of plunger pumps which draw oil from a separate outside pump, and constructed integrally with it is a gear pump which delivers the oil under about 60 pound pressure through a set of copper pipes in the base to the main bearings. The plunger oil pump shows great refinement of detail. A worm wheel and two eccentrics are machined up out of one piece and serve to operate the plungers.
Fig. 246.—Part Sectional Side View and Sectional End View of Benz 160 Horse-Power Aviation Engine.
Some interesting details of the 160 horse-power Benz motor, which is shown at [Fig. 246], are reproduced from the “Aerial Age Weekly,” and show how carefully the design has been considered.
- Maximum horse-power, 167.5 B. H. P.
- Speed at maximum horse-power, 1,500 R. P. M.
- Piston speed at maximum horse-power, 1,770 ft. per minute.
- Normal horse-power, 160 B. H. P.
- Speed at normal horse-power, 1,400 R. P. M.
- Piston speed at normal horse-power, 1,656 ft. per minute.
- Brake mean pressure at maximum horse-power, 101.2 pound per square inch.
- Brake mean pressure at normal horse-power, 103.4 pound per square inch.
- Specific power cubic inch swept volume per B. H. P., 5.46 cubic inch; 160 B. H. P.
- Weight of piston, complete with gudgeon pin, rings, etc., 5.0 pound.
- Weight of connecting rod, complete with bearings, 4.99 pound; 1.8 pound reciprocating.
- Weight of reciprocating parts per cylinder, 6.8 pound.
- Weight of reciprocating parts per square inch of piston area, 0.33 pound.
- Outside diameter of inlet valve, 68 mm.; 2.68 inches.
- Diameter of inlet valve port (d), 61.5 mm.; 2.42 inches.
- Maximum lift of inlet valve (h), 11 mm.; 0.443 inch.
- Area of inlet valve opening (π d h), 21.25 square cm.; 3.29 square inches.
- Inlet valve opens, degrees on crank, top dead center.
- Inlet valve closes, degrees on crank, 60° late; 35 mm. late.
- Outside diameter of exhaust valve, 68 mm.; 2.68 inches.
- Diameter of exhaust valve port (d), 61.5 mm.; 2.42 inches.
- Maximum lift of exhaust valve (h) 11 mm.; 0.433 inch.
- Area of exhaust valve opening (π d h), 21.25 square cm.; 3.29 square inches.
- Exhaust valve opens, degrees on crank, 60° early; 35 mm. early.
- Exhaust valve closes, degrees on crank, 161⁄2° late; 5 mm. late.
- Length of connecting rod between centers, 314 mm.; 12.36 inches.
- Ratio connecting rod to crank throw, 3.49:1.
- Diameter of crank-shaft, 55 mm. outside, 2.165 inches; 28 mm. inside, 1.102 inches.
- Diameter of crank-pin, 55 mm. outside, 2.165 inches; 28 mm. inside, 1.102 inches.
- Diameter of gudgeon pin, 30 mm. outside, 1.181 inches; 19 mm. inside, 0.708 inch.
- Diameter of cam-shaft, 26 mm. outside, 1.023 inches; 18 mm. inside, 0.708 inch.
- Number of crank-shaft bearings, 7.
- Projected area of crank-pin bearings, 36.85 square cm.; 5.72 square inches.
- Projected area of gudgeon pin bearings, 22.20 square cm.; 3.44 square inches.
- Firing sequence, 1, 5, 3, 6, 2, 4.
- Type of magnetos, ZH6 Bosch.
- Direction of rotation of magneto from driving end, one clock, one anti-clock.
- Magneto timing, full advance, 30° early (16 mm. early).
- Type of carburetors (2) Benz design.
- Fuel consumption per hour, normal horse-power, 0.57 pint.
- Normal speed of propeller, engine speed, 1,400 R. P. M.