(2) The crankshaft timing gear can be
(11) Check lube oil pump drive gear and
mounted in only one position due to its being keyed
crankshaft timing gear for worn or chipped teeth
to the crankshaft. The camshaft gear can also be
and replace if necessary.
mounted in only one position as result of the
(12) If the crankshaft is worn so that the
location of the keyway relative to the cams.
c o n n e c t i n g rod or main bearing maximum journal-
Therefore, when the engine is properly timed, the
t o - b e a r i n g shell clearance (with new shells) exceeds
m a r k i n g s on the various gears will match as shown
0.0044 inch and 0.0046 inch, or the maximum
i n figure 3-92.
j o u r n a l s taper or out-of-round is greater than 0.003
must be replaced.
inch, the crankshaft
An engine which is "out of time'" may result in
M e a s u r e m e n t s of the crankshaft should be accurate
preignition uneven running, and a loss of power.
to the nearest 0.002 inch.
( 1 ) Install upper grooved bearing shells in the
(2) Apply clean engine oil to all crankshaft
journals and set crankshaft in place.
( 3 ) Install the upper halves of the rear main
b e a r i n g thrust washers on each side of the bearing,
a n d the doweled lower halves on each side of the
rear main bearing cap.
(4) With the lower main bearing shells in-
s t a l l e d in bearing caps, tap the caps lightly with a
soft hammer to seat them properly and draw the
bearing cap bolts uniformly tight starting with
center cap and working alternately toward both
ends of the block, to 120-130 lbs.ft. torque. Tighten
the bolts to the high side of the torque specification
b u t do not exceed the limit.
I f bearings have been installed properly, the
crankshaft will turn freely with all main bearing cap
bolts drawn to specified torque.
(5) Check crankshaft end play at thrust
w a s h e r s . The crankshaft clearance with new thrust
Figure 3-92. Gear train and timing marks.
washers should be from 0.004 to 0.011 inch. In-
(3) When an engine is suspected of being out
o f time, due to an improperly assembled gear train,
misalignment of the rear main bearing. In such
a quick check can be made without having to
case, loosen the bearing cap, then retighten as
remove the flywheel and flywheel housing by
described above. If lack of clearance is still present,
following the procedure outlined below,
either dirt or a burr on the inner face of one or more
c. Checking Engine Timing. Access to the
of the thrust washers may be the cause.
crankshaft pulley, to mark the top-dead-center
(6) Refer to figure 3-88 and reassemble and
p o s i t i o n of the selected piston and to the front end
install the crankshaft. Installation is the reverse
of the crankshaft or flywheel for barring the engine
p r o c e d u r e of removal.
o v e r is necessary in performing the timing check.
3-34. Gear Train and Engine Timing.
Then, proceed as follows:
a. General. The gear train consists of a
(1) Remove the cylinder head rocker arm
crankshaft gear, and idler gear, a camshaft gear
cover (TM 10-3930-242-12).
and a balance shaft gear. The crankshaft gear,
(2) Select any cylinder for the timing check--it
camshift gear, and balance shaft gears are pressed
i s suggested that a cylinder adjacent to one of the
on and keyed to their respective shafts and each
c y l i n d e r head cover studs be chosen since the stud
g e a r is secured by a retaining nut and lock plate.
may be used for mounting a dial indicator.
The idler gear rotates on a stationary hub.
(3) Remove the fuel jumper lines (at the
b. Engine Timing.
cylinder selected) and install shipping caps on
(1) The correct relationship between the
injector fuel fittings to prevent the entry of dirt.
crankshaft and camshaft must be maintained to
M a k e sure that the valve and injector rocker arms
p r o p e r l y control fuel injection and the opening and
are in the " u p " p o s i t i o n . t h e n r e m o v e t h e r o c k e r
c l o s i n g of the exhaust valves.
shaft bracket bolts and swing the rocker arm