Mercedes Motor
The 150 horse-power six-cylinder Mercedes motor is 140 millimeters bore and 160 millimeters stroke. The Mercedes company started with smaller-sized cylinders, namely 100 millimeters bore and 140 millimeters stroke, six-cylinders. The principal features of the design are forged steel cylinders with forged steel elbows for gas passages, pressed steel water jackets, which when welded together forms the cylinder assembly, the use of inclined overhead valves operated by means of an overhead cam-shaft through rocker arms which multiply with the motion of the cam. By the use of steel cylinders, not only is the weight greatly reduced, but certain freedom from distortion through unequal sections, leaks and cracks are entirely avoided. The construction is necessarily very expensive. It is certainly a sound job. In the details of this construction there are a number of important things, such as finished gas passages, water-cooled valve guides and a very small mass of metal, which is water-cooled, surrounding the spark-plug. Of course, it is necessary to use very high compression in aviation motors in order to secure high power and economy and owing to the fact that aviation motors are worked at nearly their maximum, the heat flow through the cylinder, piston, and valves is many times higher than that encountered in automobile motors. It has been found necessary to develop special types of pistons to carry the heat from the center of the head in order to prevent pre-ignition. In the Mercedes motor the pistons have a drop forged steel head which includes the piston boss and this head is screwed into a cast iron skirt which has been machined inside to secure uniform wall thickness.
CENSORED
| Maker’s Name and Model | Num- ber of Cyl. | Bore (In.) | Stroke (In.) | Piston Displace- ment (Cubic In.) | H.P. | R.P.M. | Weight of Engine with Carburetor and Ignition | Gas Consump- tion | |||
| Aeromarine | 6 | 4 | 1⁄2 | 5 | 1⁄8 | 449 | 85 | 1400 | 440 | ... | |
| Aeromarine D-12 | 12 | 4 | 5⁄16 | 5 | 1⁄8 | ... | ... | ... | 750 | ... | |
| Curtiss OX | 8 | 4 | 5 | 502 | .6 | 90 | 1400 | 375 | ... | ||
| Curtiss OXX-2 | 8 | 4 | 1⁄4 | 5 | 567 | .5 | 100 | 1400 | 423 | ... | |
| Curtiss V-2 | 8 | 5 | 7 | 1100 | 200 | 1400 | 690 | ... | |||
| CENSORED | |||||||||||
| General Vehicle Gnome Mono | 9 | 4 | .33 | 5 | .9 | 848 | 100 | 1200 | 272 | 12 gals/hour at rated H.P. | |
| Gyro K Rotary, Le Rhone Type | 7 | 4 | 1⁄2 | 6 | ... | 90 | 1250 | 215 | 8 gals/hour at rated H.P. | ||
| Gyro L Rotary, Le Rhone Type | 9 | 4 | 1⁄2 | 6 | 859 | 100 | 1200 | 285 | 10 gals/hour at rated H.P. | ||
| Hall-Scott A-7 | 4 | 5 | 7 | 550 | 90- 100 | 1400 | 410 | ... | |||
| Hall-Scott A-5 | 6 | 5 | 7 | 825 | 125 | 1300 | 592 | ... | |||
| Hispano-Suiza | 8 | 4 | 5⁄8 | 5 | 672 | 154 | 1500 | 455 | ... | ||
| Knox Motors Co. | 12 | 4 | 3⁄4 | 7 | 1555 | 300 | 1800 | 1425 | 31.5 gals/hour | ||
| Maximotor A-6 | 6 | 4 | 1⁄2 | 5 | 477 | 85 | 1600 | 340 | ... | ||
| Maximotor B-6 | 6 | 5 | 6 | 706 | .8 | 115 | 1600 | 385 | ... | ||
| Maximotor A-8 | 8 | 4 | 1⁄2 | 5 | 636 | 115 | 1600 | 420 | ... | ||
| Packard 12 | 12 | 4 | 6 | 903 | 225 | 2100 | 800 | ... | |||
| Sturtevant 5 | 8 | 4 | 5 | 1⁄2 | 552 | .9 | 140 | 2000 | 580 | ... | |
| Sturtevant 5-A | 8 | 4 | 5 | 1⁄2 | ... | 140 | 2000 | 514 | 13.75 gals/hour | ||
| Thomas 8 | 8 | 4 | 5 | 1⁄2 | 552 | .9 | 135 | 2000 | 630 lbs. with self-starter | ... | |
| Thomas 88 | 8 | 4 | 1⁄8 | 5 | 1⁄2 | 552 | .9 | 150 | 2100 | 525 lbs. with self-starter | ... |
| Wisconsin | 6 | 5 | 6 | 1⁄2 | 765 | .7 | 140 | 1380 | 637 | ... | |
| Wisconsin | 12 | 5 | 6 | 1⁄2 | 1531 | .4 | 250 | 1200 | ... | ... | |
The carburetor used on this 150 horse-power Mercedes motor is precisely of the same type used on the Twin Six motor. It has two venturi throats, in the center of which is placed the gasoline spray nozzle of conventional type, fixed size orifices, immediately above which are placed two panel type throttles with side outlets. An idling or primary nozzle is arranged to discharge above the top of the venturi throat. The carburetor body is of cast aluminum and is water jacketed. It is bolted directly to air passage passing through the top and bottom half of the crank-case which passes down through the oil reservoir. The air before reaching the carburetor proper to some extent has cooled the oil in the crank chamber and has itself been heated to assist in the vaporization. The inlet pipes themselves are copper. All the passages between the venturi throat and the inlet valve have been carefully finished and polished. The only abnormal thing in the design of this motor is the short connecting rod which is considerably less than twice the stroke and would be considered very bad practice in motor car engines. A short connecting rod, however, possesses two very real virtues in that it cuts down height of the motor and the piston passes over the bottom dead center much more slowly than with a long rod.
Other features of the design are a very stiff crank-case, both halves of which are bolted together by means of long through bolts, the crank-shaft main bearings are seated in the lower half of the case instead of in the usual caps and no provision is made for taking up the main bearings. The Mercedes company uses a plunger type of pump having mechanically operated piston valves and it is driven by means of worm gearing.
The overhead cam-shaft construction is extremely light. The cam-shaft is mounted in a nearly cylindrical cast bronze case and is driven by means of bevel gears from the crank-shaft. The vertical bevel gear shaft through which the drive is taken from the crank-shaft to the cam-shaft operates at one and one-half times the crank-shaft speeds and the reduction to the half-time cam-shaft is secured through a pair of bevels. On this vertical shaft there is mounted the water pump and a bevel gear for driving two magnetos. The water pump mounted on this shaft tends to steady the drive and avoid vibration in the gearing.
The cylinder sizes of six-cylinder aviation motors which have been built by Mercedes are
| Bore | Stroke | Horse-power |
| 105 mm. | 140 mm. | 100 |
| 120 mm. | 140 mm. | 135 |
| 140 mm. | 150 mm. | 150 |
| 140 mm. | 160 mm. | 160 |
The largest of these motors has recently had its horsepower increased to 176 at 1450 R. P. M. This general design of motor has been the foundation for a great many other aviation motor designs, some of which have proved very successful but none of which is equal to the original. Among the motors which follow more or less closely the scheme of design and arrangement are the Hall-Scott, the Wisconsin motor, the Renault water-cooled, the Packard, the Christofferson and the Rolls-Royce. Each of these motors show considerable variation in detail. The Rolls-Royce and Renault are the only ones who have used the steel cylinder with the steel jacket. The Wisconsin motor uses an aluminum cylinder with a hardened steel liner and cast-iron valve seats. The Christofferson has somewhat similar design to the Wisconsin with the exception that the valve seats are threaded into the aluminum jacket and the cylinder head has a blank end which is secured to the aluminum casting by means of the valve seat pieces. The Rolls-Royce motors show small differences in details of design in cylinder head and cam-shaft housing from the Mercedes on which it has taken out patents, not only abroad but in this country.