e casting. This saved weight because heavy
flanges, nuts, and bolts were dispensed with. The cylinders, instead of
being bolted to the crankcase, as was normal practice, were held in
position by two circular hoops of alloy steel passing over the cylinder
flanges. They were tightened to such an extent that at no time did the
cylinders transfer any tension loads to the crankcase. This type of
fastening actually strengthened the crankcase in contrast to the usual
method. For this reason it could be built lighter. The hoops did not
always function well. "The first job I ever did on the Towle was to
patch the holes in the top and bottom of the hull when a cylinder blew
off during run-up and nearly beheaded the pilot."[13]

[Illustration: Figure 22.--Rear view of engine with rear crankcase cover
removed, showing valve and injector rocker levers and injector control
ring mounted on crankcase diaphram. U.S. Navy test, 1931. (Smithsonian
photo A48323D.)]

[Illustration: Figure 23.--Main crankcase. U.S. Navy test, 1931.
(Smithsonian photo A48325B.)]

[Illustration: Figure 24.--Rear crankcase cover and gear train:
crankshaft gear drives B, which drives oil pump at F. A, integral with
B, drives internal cam gear. B also drives C on fuel-circulating pump.
D, driven by crankshaft gear, drives E on generator shaft. U.S. Navy
test, 1931. (Smithsonian photo A48325C.)]

[Illustration: Figure 25.--Master and link connecting rods. U.S. Navy
test, 1931. (Smithsonian photo A48323A.)]

[Illustration: Figure 26.--Crankshaft with automatic-timing retarding
device on rear end of pivoted- and spring-mounted counterweights. U.S.
Navy test, 1931. (Smithsonian photo A48323B.)]

[Illustration: Figure 27.--Propeller hub and vibration damper. U.S. Navy
test, 1931. (Smithsonian photo A48325A.)]

Crankshaft: Since this engine developed the high maximum cylinder
pressure of 1500 psi, it was necessary to protect the crankshaft from
the resulting heavy stresses. Without such protection the crankshaft
would be too large and heavy for practical aeronautical applications.
Although the maximum cylinder pressures were 10 times as great as the
average ones, they were of short duration. The method of protecting the
crankshaft took full advantage of this fact. It consisted of having the
counterweights flexibly mounted instead of being rigidly bolted, as was
common practice. The counterweights were pivoted on the crank cheeks.
Powerful compression spring