Table of Contents
Advertisement
Section 2
GENERAL DESCRIPTION
1. DIFFERENCES IN ENGINE MODELS
a. General.
The higher power developed by C-145
engines is the result of a combination of a longer pis-
ton stroke and a higher rated crankshaft speed.
The
longer stroke produces a higher compression ratio,
making necessary the use of fuel of a higher octane
rating, and a larger total piston displacement, which
increases total fuel consumption. Specific fuel con-
sumption of both models is approximately. 5 lbs. per
brake horsepower per hour at cruising speed and
manifold pressure. Model C-145 has a slightly lower
specific fuel consumption at its most efficient opera-
ting speed. These differences in dimensions require
different carburetor metering parts.
b. Pistons.
All three compression rings are the
same type in the two types of piston assembly and are
fitted in grooves above the piston pin. The slotted oil
control ring in the C-125 piston assembly is also
above the pin - in the fourth groove, while the similar
oil control ring in the C-145 piston assembly is placed
in a groove near the bottom of the skirt and is dimen-
Sionally slightly different. Connecting rod space be-
tween piston pin bosses in the C-145 piston is narrow-
er than in the C-125 piston. All piston pins currently
produced have pressed-in aluminum end plugs to pre-
vent excessive plug rotation and wear. This type of
pin assembly must be used in all C-145 engines;
however, the former type of pin assembly with loose
end plugs may be used in C-125 pistons as long as
parts are serviceable or repairable by replacement
of plugs.
c. Connecting Rods.
C-145 connecting rods have
shorter piston pin bosses and bushings than those of
model C-125. Crankpin bearing inserts installed in
early production C-145 connecting rods were Tri-
Metal bronze.
These have been superseded by the
same type of bearing used in C-125 connecting rods.
d. Crankshafts.
C-145 crankshafts have a slightly
longer crank throw than those of model C-125. (Refer
to Section 1 for dimensions. ) Early production C-145
crankshafts had no counterweights and were identified
by a 1/4 in. diameter hole drilled between propeller
bolt bushings through the propeller flange. Current
production C-145 crankshafts have two floating coun-
terweights loosely pinned to extensions each Side of
the cheek between No's it and 2 craukpi..o.s.
'The
na-
tural . frequency of oscillation of the weight on the
notched crankshaft extension is adjusted, by size of
its bushings, to dampen out the fifth overtone of crank-
vibration, while the other counterweight dampens
t"~
sixth overtone, preventing excessive vibration of the
crankshaft gear and wear of gear teeth. C-125 crank-
shafts do not have or require the dynamic damper
weights. Crankshafts of model C-145-2H have an oil
inlet hole through the front main journal, whose hollow
interior has a permanent plug at the rear and a re-
movable plug at the front, providing an oil passage to
the shaft end for hydraulic actuation of the controllable
propeller.
The letter "D" in a C-145 serial No. de-
notes a dampened shaft, ,
6
e. Camshafts and Valve Lifters. All C-125 engines
are equipped with cast iron camshafts and steel faced
valve lifters. Earlyproduction C-145 engines had the
same type of lifters and cast iron camshafts of special
design. Current production C-145 engines have forged
steel camshafts and valve lifters whose bodies are
single piece iron castings. The forged steel camshafts
are copper plated, between lobes and journals, on the
unfinished surfaces, and the entire surface is Parko-
Lubrite coated for protection until the shafts are in-
stalled. This is a soft, black coating which rubs off
easily if the parts are carelessly handled.
It
is es-
sential that the proper type of valve lifter bodies be
installed with each type of camshaft.
It
is recom-
mended that forged steel camshafts and cast iron lifter
bodies be installed in all C-145 engines - not already
so equipped - at the next major overhaul.
f.
Crankcases.
Engines have crankcases in which
the two shorter through studs and seven of the longer
ones are replaced by headless through bolts which also
act as dowels to align the halves. Two long and one
short dowel bolts used in parting flange holes of the
old type case are not installed in the current type.
The new type cases may be installed in any C-125-2
engine or in any C-145-2 engine. All C-145-2H en-
gines have crankcases of the new type, but these have
a special valve near the front end of the left oil gallery
to control oil flow to the special crankshaft passage.
g.
Oil Sumps.
The sump assemblies installed in
C-145 engines have baffles in the intake air passages.
The baffle is not used in C-125 sumps.
2. CYLINDER CONSTRUCTION
Heat-treated aluminum alloy cylinder heads are
screwed and shrunk to replaceable forged steel bar-
rels. Closely spaced cooling fins on both the cylinder
heads and cylinder barrels provide am:ple heat-dissi-
pating surface with minimum resistance to air flow.
Cylinder bores are ground to a certain finish specified
in the Table of Limits, Section 13.
Stainless steel
helical-coil spark plug inserts are screwed in place.
Rocker boxes are cast integral with cylinder heads and
are provided with lightweight covers made of deep
drawn sheet metal.
Underside exhaust ports permit
a more compact installation and a more positive ex-
haust scavenging.
3. PISTON AND PISTON PIN CONSTRUCTION
a. Pistons are heat-treated aluminum alloy castings.
The ring grooves are fitted with chrome faced top
compression rings, plain cast iron 2nd. and 3rd. com-
pression rings and slotted bottom oil control rings.
Holes drain oil from the bottom ring groove to the
interior.
b. The full-floating piston pin is a case-hardened,
seamless alloy steel tube with aluminum plugs
pressed into its ends. The plugs are finish machined
after assembly, and the pin is ground to final size and
pOlished.
Advertisement
Table of Contents
