The camshaft and valve gear are above the cylinder head as in the Mercedes, but the lubrication of the parts was improved upon by the Packard Company.
The crankshaft follows standard 12 cylinder practice except as to the oiling system, the latter following German practice rather closely. The first system used one pump to keep the crankcase empty delivering the oil to an outside reservoir. A second pump took the oil from the reservoir and delivered it to the main crankshaft bearings under pressure. The overflow from the main bearings traveled out over the face of the crank throw cheeks to a "Scupper," which collected the excess for crank pin lubrication. In the present system, a similar general method is followed except that the pressure oil is not only fed to the main crankshaft bearings, but also through holes in the crank cheeks to the crank pins instead of by the former scupper feed.
A special Zenith carburetor is used, that is particularly adapted to the Liberty motor. A Delco ignition system of special form is installed to meet the peculiar cylinder block angle of 45 degrees. This ignition is of the electric generator type and magnetos are not used.
Several American records have been broken by the new motor, and it is reported to have given very satisfactory service, but full details of the performance are difficult to obtain owing to the strict censorship maintained in regard to things aeronautic. The motor is particularly well adapted to heavy bombing and reconnaissance type machines, or for heavy duty. It is reported that the use of the motor has been discontinued on speed scouts, although further developments along this line may not have been reported.
The following gives the principal characteristics of the Liberty motor, issued by the National Advisory Committee for Aeronautics.
| Year (Model) | Horse-power | Weight Pounds | Weight Per H. P. | Gasoline H. P. Hour |
| 1917 | 400 | 801 | 2.00 | 0.50 |
| 1918 | 432 | 808 | 1.90 | 0.48 |
| 1918 | 450 | 825 | 1.80 | 0.46 |
The motors listed are all 12 cylinder models, and the output and unit weights are based on a crank-shaft speed of 1800 R. P. M. The 5" x 7" bore and stroke give an output of 37.5 horsepower per cylinder in the latest model. In 1917, the Liberty motor was 65 per cent more powerful, and 28 per cent lighter, than the average stock motor in service during that year.
CHAPTER XXI. GLOSSARY OF AERONAUTICAL WORDS.
In the following list are the most common of the aeronautical words and phrases. Many of these words are of French origin, and in such cases are marked "Fr." In cases of English words, the French equivalents follow in parentheses. When a French word or term is given it is in italics, unless it is in common use in this country. Words marked (*) are the revisions adopted by the National Advisory Board of Aeronautics at Washington, D. C., and include the term "Airplane," which was intended to supplant the more common "Aeroplane." These revisions have not met with universal adoption, for the older words are too well established to admit of change.