Copyright by Goodheart-Willcox Co., Inc.
Chapter 23 Front End Service 507
Loosen or
tighten bolt
Hold
camshaft
Wrench on
camshaft flat
Camshaft
Camshaft
sprocket
Figure 23-14. A flat surface is frequently ground on the cam-
shaft so a wrench can be used to hold the camshaft stationary
when removing or installing the camshaft sprocket. With some
engine designs, a special camshaft holding device is needed.
(General Motors)
Timing marks
align
Tensioner
Timing marks
align
Check that
belt teeth
are fully
into sprocket
teeth
Figure 23-15. This is a typical OHC engine with the timing belt
installed.
Pry on the
bracket, not
the wheel
Loosen the
bolt and
adjust the belt
Timing
belt
Nut locks
the
tensioner
Figure 23-16. This timing belt adjuster has a slot that lets you
swivel adjuster to the side. Pry on the adjuster and tighten the
fastener. Then, check for proper timing belt tension.
3. Fit the crankshaft sprocket into position, as was
described earlier for a timing chain.
4. Torque the crankshaft snout bolt to specifications.
5. Turn the sprockets until the timing marks align or until
number one piston is at TDC on the compression
stroke.
Installing the Timing Belt
Since exact belt installation procedures vary, refer
to the service manual. It will explain special methods
for aligning timing marks, positioning the camshaft and
crankshaft, and installing the belt tensioner. Figure 23-15
shows the front view of an OHC engine with the timing
belt in place. Note how the timing marks align.
If the timing belt is to be reused, the direction of rotation
should have been marked on the belt before removal. A
reused belt must be installed so that it rotates in the same
direction as before. This will prevent premature failure.
Adjusting Belt Tension
It is important that timing belt tension is adjusted
properly. If too loose, the belt could flap or vibrate in
service and fly off its sprockets. If too tight, the timing belt
could snap. Both could lead to severe valve damage. The
service manual will detail how to properly adjust tension.
Figure 23-16 shows a belt tensioner. Note how you
can loosen the attaching bolts and swivel the tensioner.
Pry on the tensioner bracket to preload the belt. Do not
pry on the wheel.
Figure 23-17 shows a special tool used to correctly
set belt tension. The adjusting tool is turned with a wrench
until the belt gauge reads within specifications. Tighten the
tensioner bracket bolts to secure the adjustment.
Figure 23-18 shows how one manufacturer recom-
mends using a battery hold-down bolt to pretension the
timing belt. You must turn the prong on the battery hold-
down bolt with your fingers to hold the tensioner in place
while working.
There is a simple way to check timing belt tension if a
gauge or tool is not available. Adjust the belt tension until
moderate finger and thumb pressure is needed to twist the
belt about one-quarter turn. This should provide good belt
service.
After installing and tensioning the belt, rotate the
engine by hand. Use a wrench on the crankshaft snout
bolt. Turn the crank in the direction of normal rotation until
the timing marks come around and realign. Then, double-
check alignment of the timing marks.