Copyright by Goodheart-Willcox Co., Inc.
Chapter 23 Front End Service 509
Timing gear
Press ram
Flat feeler
gauge
Thrust
washer
Camshaft
Figure 23-21. This particular timing gear must be pressed onto
the camshaft snout. Clearance must be maintained between
the thrust plate and the camshaft cheek to allow proper cam-
shaft endplay. (Ford)
Indicator
stand
Indicator stem
Dial indicator
reading
equals runout
Figure 23-22. Measuring timing gear runout or wobble. (Ford)
Dial indicator
Feeler gauge
Wiggle gear
back and forth
Figure 23-23. Measuring timing gear backlash.
Timing gears can usually be installed with light blows
from a brass hammer. Make sure the keys and keyways are
aligned. Also, make sure all timing marks are aligned. Tap
in a circular motion around the gear to force it squarely into
position. Do not hit and damage the gear teeth. A press may
be needed to install the camshaft gear onto the camshaft.
Figure 23-21 shows how a press is used to service the
camshaft gear on the camshaft. With this engine design,
the camshaft must be out of the engine for timing gear
replacement. A clearance must be maintained between the
thrust plate and the camshaft cheek. This clearance allows
for proper camshaft endplay.
Double-check the alignment of the timing marks. The
timing marks must be positioned properly to time the cam-
shaft with the crankshaft.
Measuring Timing Gear Runout
Timing gear runout or wobble is measured with a dial
indicator. To measure timing gear runout:
1. Position the indicator stand on the engine block. Place
the indicator stem on the outer edge of the camshaft
timing gear. The stem should be parallel with the cam-
shaft centerline, as shown in Figure 23-22.
2. Turn the engine crankshaft while noting indicator
needle movement.
3. The indicator reading equals the runout.
4. If runout is greater than specifications, remove the
timing gears and check for problems. The gear may
not be fully seated or it may be machined improperly.
Also, check the camshaft for runout or straightness.
Measuring Timing Gear Backlash
Timing gear backlash is the amount of clearance
between the timing gear teeth. Too little clearance can
make the gears lock up when expanded by engine
heat. Too much clearance can reduce engine power
and increase gear noise. Backlash can also be used to
determine timing gear teeth wear. Use a dial indicator to
measure timing gear backlash.
1. Set the indicator stand on the engine. Look at
Figure 23-23.
2. Locate the indicator stem on one of the camshaft gear
teeth. The stem must be parallel with gear tooth travel.
3. Move the camshaft gear one way and then the other,
without turning the crankshaft.
4. Observe the indicator needle. The needle travel is
equal to the backlash.
Refer to the service manual for backlash specifica-
tions. If timing gear backlash is greater than specifications,
the gears are worn. They should be replaced.
If a dial indicator is not available, backlash can be
measured with a feeler gauge. The size of the blade that fits
between the gear teeth equals the backlash.