TM 9-4940-421-14
to top dead-center. Use a ring compressor to compress
wear in the cylinder bore, the taper and out-of-round
the piston rings.
condition.
f. Installation of Connecting Rod and piston.
(4) Clean the carbon from the top of the piston.
(1) Lower the piston into the cylinder. Using the
Clean the ring gooves with a ring groove tool or a piece
butt end of a hammer handle, carefully push the piston
of an old ring.
and connecting rod into the cylinder until connecting
(5) Wash all of the parts in cleaning solvent and
rod rests on the crankshaft. This action will release the
blow dry with compressed air (app D).
piston ring compressor.
(6) To measure the piston ring gap, place the ring
(2) Assemble the lower rod cap. A number is
into the cylinder bore in the approximate operating
stamped on each rod and cap to insure matching of the
position, and measure the gap with a feeler gage. The
parts. Make sure the numbers agree for each rod and
gap clearance should be between 0.010 to 0.020 inch.
cap. Push the piston down while rotating the
(7) Invert the piston and slide it into the cylinder
crankshaft to bottom dead-center. Position the cap on
bore. Check the piston-to-cylinder clearance at the
the rod so that its oil hole faces the oil spray nozzle.
piston skirt. The clearance should be 0.0037 to 0.0042
Secure the assembly with nuts (7) and tighten each nut
inch. The clearance must be measured at the center of
to 26-32 ft. lbs. torque.
the thrust face, at the bottom of the piston skirt.
(3) Using a suitable feeler gage, measure the side
( 8 ) Measure the piston ring side clearance.
clearance between the bearing and crankshaft. The
Replace the piston if the side clearance is not within
clearance should measure at least 0.009 inch and not
the following tolerances.
more than 0.016 inch.
Topring . . . . . . . . . . . . . . . ..0.0015 to 0.0035 inch
(4) Install the oil pump. Refer to paragraph 6-15.
2nd and 3rd ring . . . . . . . . . 0.0015 to 0.0035 inch
(5) Install the cylinder heads. Refer to paragraph
Oilring . . . . . . . . . . . . . . . . ..0.002 to 0.004 inch
6-11.
(9) Measure the fit of the piston pin in the piston.
The clearance should measure 0.0000 to 0.0008 inch.
6-18. CRANKSHAFT AND CAMSHAFT.
(10) Check the piston pin bushing in the connect-
a. General. The crankshaft is supported at both ends
ing rod for wear, scoring, or out-of-round condition.
by roller bearings. The outer race or cup of the bearing
The clearance between the piston pin and bushing
at the drive end of the engine is carried in the main
should be 0.0005 to 0.0011 inch. Replace bushing as
bearing plate, which is secured to the crankcase with
necessary.
capscrews and lockwashers. Shims are installed be-
NOTE
tween the bearing plate and crankcase to provide the
When pressing in new bushings, be careful to aline the oil
proper crankshaft end play. The camshaft operates the
hole in the bushing with the oil hole in the connecting rod.
valve tappets and fuel pump adapter. The cams and
(11) Inspect the connecting rod bearing halves for
fuel pump eccentric are integral with the shaft. The
wear or scoring. Check the bearing to crank pin
two camshaft journals ride in honed bores in the
clearance; it should be between 0.0013 and 0.0035 inch.
crankcase.
Replace if worn beyond the limits.
b. Removal of the Crankshaft.
e. Reassembly of Connecting Rod and Piston.
(1) Remove the cylinder heads and valves (para
(1) Using a fiber hammer, tap the piston pin (5,
NOTE
(2) Remove the fuel pump adapter (para 6-4).
Each piston and connecting rod is marked for its cylinder;
(3) Remove the gear cover (para 6-15a(2)).
make sure that the parts are assembled in the proper posi-
NOTE
tion.
When removing camshaft and idler gear, tag each gear to
(2) Place the proper connecting rod (7) in the
facilitate installation.
matched piston so that the oil hole in the connecting
(4) Remove the idler and camshaft gears (para
rod cap is correct. Tap the piston pin into the other bore
of the piston, and install the two retaining rings (6).
(5) Remove the connecting rods and pistons (para
(3) Expand the oil ring (3) and install it in the bot-
tom groove of the piston skirt. Next, install the scraper
NOTE
ring (2). Mount the scraper ring with scraper edge
Keep the shims together so that the same shims will be
down. Install the compression rings (l). Stagger the
reinstalled. If any are damaged, replace them with shims of
the same thickness.
piston ring gaps 90 degrees apart around the piston.
(6) Remove the six capscrews and lockwashers
(4) Fit the connecting rod bolts (8) in the rod, and
that secure the main bearing plate to the crankcase.
fit the upper bearing half so that the oil hole in the
Pry off the bearing plate, gaskets and any installed
bearing alines with the oil hole in the rod. Lightly oil
shims.
the piston, piston rings and cylinder walls. Turn the
(7) Slide the oil slinger (12, fig 6-14) from the
crankshaft journal, to which the rod is to be attached,
