TM 5-3895-346-14
ENGINE OVERHAUL
GEAR TRAIN AND TIMING
Effective with engine serial number 4D-65954, all Series 53 vehicle engines are built with advanced timing.
The timing is advanced by aligning the proper A timing mark on the crankshaft gear with the circle-triangle
timing mark on the idler gear.
The camshaft and balance shaft gears are positioned so that the circle timing marks are adjacent to each other
(Fig. 1). One circle-triangle timing mark on the idler gear is aligned with the second circle on the mating cam-
shaft (or balance shaft) gear. The other timing mark on the idler gear is aligned with the proper timing mark on
the crankshaft gear.
The crankshaft gear is stamped IR-A on the left side of the circle timing mark (Fig. 1) for a right-hand rotation
engine. For standard timing, the circle on the crankshaft gear is aligned with the circle-triangle on the idler
gear. For advanced timing, the A adjacent to the IR on the crankshaft gear is aligned with the circle-triangle on
the idler gear.
Lubrication
The gear train is lubricated by the overflow of oil from the camshaft and balance shaft pockets spilling into the
gear train compartment. A certain amount of the oil also spills into the gear train compartment from the cam-
shaft and balance shaft end bearings and the idler gear bearing. The blower drive gear bearing on the four-
cylinder, in-line engine is lubricated through an external pipe leading from the cylinder block, main oil gallery to
the gear hub support.
Engine Timing
The correct relationship between the crankshaft and camshaft(s) must be maintained to properly control fuel
injection and the opening and closing of the exhaust valves.
The crankshaft timing gear can be mounted in only one position since it is keyed to the crankshaft. The cam-
shaft gear(s) can also be mounted in only one position due to the location of the keyway relative to the cams.
Therefore, when the engine is properly timed, the markings on the various gears will match as shown in Fig. 1.
Pre-ignition, uneven running, and a loss of power may result if an engine is out of time.
When an engine is suspected of being out of time due to an improperly assembled gear train, a quick check
can be made without removing the flywheel and flywheel housing by following the procedure outlined below.
Check Engine Timing
Access to the crankshaft pulley, to mark the top dead center position of the selected piston, and to the front end
of the crankshaft or the flywheel for turning the crankshaft is necessary when performing the timing check.
Then proceed as follows:
1.
Clean and remove the valve rocker cover.
2.
Select any cylinder for the timing check.
3.
Remove the injector as outlined in Fuel Injector.
4.
Carefully slide a rod, approximately 12 inches long, through the injector tube until the end of the
rod rests on top of the piston. Place the throttle in the no-fuel position. Then turn the crankshaft
slowly in the direction of engine rotation. Stop when
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