ankshafts that
were made were quenched in this manner.

PISTON PIN

The piston pin on an aviation engine must possess maximum resistance
to wear and to fatigue. For this reason, the piston pin is considered,
from a metallurgical standpoint, the most important part on the
engine to produce in quantities and still possess the above
characteristics. The material used for the Liberty engine piston
pin was S. A. E. No. 2315 steel, which is of the following chemical
composition: Carbon, 0.100 to 0.200 per cent; manganese, 0.500
to 0.800 per cent; phosphorus, 0.040 maximum per cent; sulphur,
0.045 maximum per cent; nickel, 3.250 to 3.750 per cent.

Each finished piston pin, after heat treatment, must show a minimum
scleroscope hardness of the case of 70, a scleroscope hardness of
the core of from 35 to 55 and a minimum crushing strength when
supported as a beam and the load applied at the center of 35,000
lb. The heat treatment used to obtain the above physical properties
consisted in carburizing at a temperature not to exceed 1,675 deg.F.,
for a sufficient length of time to secure a case of from 0.02 to
0.04 in. deep. The pins are then allowed to cool slowly from the
carbonizing heat, after which the hole is finish-machined and the
pin cut to length. The finish heat treatment of the piston pin
consisted in quenching in oil from a temperature of from 1,525 to
1,575 deg.F. to refine the grain of core properly and then quenching in
oil at a temperature of from 1,340 to 1,380 deg.F. to refine and harden
the grain of the case properly, as well as to secure proper hardness
of core. After this quenching, all piston pins are tempered in oil
at a temperature of from 375 to 400 deg.F. A 100 per cent inspection
for scleroscope hardness of the case and the core was made, and
no failures were ever recorded when the above material and heat
treatment was used.

APPLICATION TO THE AUTOMOTIVE INDUSTRY

The information given on the various parts of the Liberty engine
applies with equal force to the corresponding parts in the construction
of an automobile, truck or tractor. We recommend as first choice for
carbon-steel screw-machine parts material produced by the basic
open hearth process and having the following chemical composition;
Carbon, 0.150 to 0.250 per cent; manganese, 0.500 to 0.800 per
cent; phosphorus, 0.045 maximum per cent; sulphur, 0.075 to 0.150
per cent.

This material is very uniform and is nearly as free cutting as