Gear Train and Timing
DETROIT DIESEL 53
the gear train compartment from the camshaft end
The gear train is lubricated by the overflow of oil from
The idler gear bearing and the accessory (fuel pump)
the camshaft pockets spilling into the gear train
drive gear is lubricated by oil directly from the cylinder
compartment. A certain amount of the oil also spills into
block main oil gallery to the bearing hubs.
spindle movement of at least I". Provide an extension
The correct relationship between the crankshaft and
for the indicator spindle. The extension must be long
camshaft(s) must be maintained to properly control fuel
enough to contact the piston just before it reaches the
injection and the opening and closing of the exhaust
end of its upward stroke. Also, select suitable mounting
attachments for the indicator so it can be mounted over
the injector tube in the cylinder head.
The crankshaft timing gear can be mounted in only one
position since it is keyed to the crankshaft. The
6. Mount the indicator over the injector tube. Check to
camshaft gear(s) can also be mounted in only one
be sure the indicator spindle extension is free in the
position due to the location of the keyway relative to the
injector tube and is free to travel at least one inch.
cams. Therefore, when the engine is properly timed, the
markings on the various gears will match as shown in
7. Attach a suitable pointer to the engine lower front
cover. The outer end of the pointer should extend out
over the top of the crankshaft pulley.
Pre-ignition, uneven running and a loss of power may
result if an engine is "out of time".
8. Turn the crankshaft slowly, in the direction of engine
rotation, until the indicator hand just stops moving.
When an engine is suspected of being out of time, due
to an improperly assembled gear train, a quick check
9. Continue to turn the crankshaft, in the direction of
can be made without removing the flywheel and
rotation, until the indicator starts to move again. Now
flywheel housing by following the procedure outlined
set the indicator on zero and continue to turn the
crankshaft until the indicator reading is .010".
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 Section 2.1.1.
* Indicator readings shown are nominal values.
4. Carefully slide a rod, approximately 12" long,
allowable tolerance is +.005 ;n.
through the injector tube until the end of the rod rests on
top of the piston. Place the throttle in the no-fuel
(2) Low velocity type injector com.
Then, turn the crankshaft slowly in the
direction of engine rotation. Stop when the rod reaches
the end of its upward travel. Remove the rod and turn
the crankshaft, opposite the direction of rotation,
between 1/16 and 1/8 of a turn.
5. Select a dial indicator with .001" graduations and a
1972 General Motors Corp.