Gear Train and Engine Timing

TM 10-3930-242-34

also be mounted in only one position as result of

the bearing cap bolts unlformly tight starting

the location of the keyway relative to the, cams.

with center cap and working alternately toward

Therefore, when the engine is properly timedd,

both ends of the block, to 120-130 foot-pounds

the markings on the various gears will match as

torque. Tighten the bolts to the high side of the

shown in figure 3-63.

torque specification but do nut exceed the limit.

( 3 ) When an engine is suspected of being

NOTE

o u t of time, due to an improperly assembled

If bearings have been installed properly, the

gear train, a quick check can be made without

crankshaft will turn freely with all main bearing

having to remove the flywheel and flywheel

cap bolts drawn to specified torque.

h o u s i n g by following the procedure outlined

(5) Check crankshaft end play at thrust

below.

w a s h e r s . The cranks shaft clearance with new

c . Checking Engine Timing. Access to the

thrust washers should be from 0.0040.011 inch.

c r a n k s h a f t pulley, to mark the top-dead-center

I n s u f f i c i e n t clearance will usually denote mis-

position of the selected piston and to the front

a l i g n m e n t of the rear main bearing. In such

end of the crankshaft or flywheel for barring the

c a s e , loosen the bearing cap, then retighten as

engine over is necessary in performing the tim-

described above. If lack of clearance is still pres-

ing check. Then, proceed as follows:

ent, either dirt or a burr on the inner face of one

( 1 ) Remove the cylinder head rocker arm

or more of the thrust washers may be the cause.

cover (TM 10-3930-242-12).

(6) Refer to figure 3-62 and install the

(2) Select any cylinder for the timing

crankshaft.

checkit is suggested that a cylinder adjacent to

( 7 ) Reposition the rocker arms and adjust

one of the cylinder head cover studs be chosen

(para 3-15).

since the stud may be used for mounting a dial

(8) Install the fuel oil pipes on the fuel in-

indicator.

j e c t o r s (para 3-14), and install the rocker arm

cover (TM 10-3930-242-12).

(3) Remove the fuel jumper lines (at the cy-

( 9 ) Install the front cover and oil pump

linder selected) and install shipping caps on in-

(para 3-2).

jector fuel fittings to prevent the entry of dirt.

(10) Install the flywheel housing (para 3-22).

M a k e sure that the valve and injector rocker

(11) Install the oil screen and inlet pipe (para

arms are in the "up" position, then remove the

3-25).

rocker shaft bracket bolts and swing the rocker

(12) Install the oil pan (para 3-24).

arm assemblies back out of the way. Remove the

(13) Install the engine (para 2-5).

i n j e c t o r assembly.

(4) Carefully place (do not drop) a welding

3-33. Gear Train and Engine Timing

r o d or drill rod approximately 12 inches long

a. General. The gear train consists of a crank-

through the injector hole and on top of the pis-

shaft gear, and idler gear, a camshaft gear and a

ton. With the throttle in the NO FUEL position,

b a l a n c e shaft gear. The crankshaft gear, cam-

b a r the crankshaft slowly in the direction of

s h a f t gear, and balance shaft gears are pressed

r o t a t i o n of the engine, and stop barring when

on and keyed to their respective shafts and each

t h e rod reaches the end of its upward travel.

gear is secured by a retaining nut and lock

Remove the rod and bar the crankshaft opposite

p l a t e . The idler gear rotates on a stationary

the direction of rotation between 1/16 and 1/8 of a

hub.

turn.

(5) Select a dial indicator having 0.001 inch

b . Engine Timing.

graduations and with a spindle movement of at

(1) The correct relationship between the

least 1 inch. Use suitable mounting attach-

c r a n k s h a f t and camshaft must be maintained to

ments for the indicator so that it can be

p r o p e r l y control fuel injection and the opening

m o u n t e d over the injector hole in the cylinder

a n d closing of the exhaust valves.

head. Provide an extension for the spindle of the

NOTE

indicator. The extension must be long enough to

An engine which is "but of time" may result in

contact the piston as it is approaching its upper

preignition, uneven running, and a loss of power.

position.

(2) The crankshaft timing gear can be

( 6 ) Mount the indicator over the injector

h o l e and tighten mountings sufficiently to hold

m o u n t e d in only one position due to its being

t h e indicator rigid.

k e y e d to the crankshaft. The camshaft gear can

3-74