Copyright by Goodheart-Willcox Co., Inc.
Chapter 23 Front End Service 503
Wrench
You can
also wiggle
here, 1/2″
(13 mm) being
maximum slack
Scale
Maximum
movement
1/8″ (3 mm)
Figure 23-2. Timing chain wear can be checked by rotating the
crankshaft back and forth. If sprocket rotation is excessive, the
chain and sprockets should be replaced. You can also check
for wear by measuring the deflection of the chain. (Chrysler)
Figure 23-3. Make sure the crankshaft key is undamaged and
properly installed in the crankshaft snout. Light hammer taps
can be used to insert the key squarely into its groove. Some
engines have two crankshaft keys.
Timing
marks
Figure 23-4. The timing marks must align when the chain and
sprockets are installed, as shown here. Refer to the service
manual for the engine on which you are working.
Others allow you to reuse steel sprockets if they are not
excessively worn.
Some camshaft sprockets have plastic teeth. The
plastic teeth are prone to wear and failure. Plastic or fiber
timing sprockets should be replaced whenever they are
removed or disassembled for service.
If the timing chain has a tensioner, check it for wear.
The fiber rubbing block can wear down and its spring can
loose tension. Replace all parts as needed.
Installing a Timing Chain
Before installing a timing chain, make sure the
crankshaft key is the correct size, unworn, and properly
installed in its groove. Refer to Figure 23-3. Also, check
that the camshaft is installed properly. If needed, mea-
sure camshaft endplay and check any fasteners holding a
thrust plate on the front of the engine, as described in the
previous chapter.
You must align timing marks on the crankshaft
sprocket and camshaft sprocket, Figure 23-4. Timing marks
may be dots, lines, circles, or other shapes indented or cast
into the timing sprockets. Sometimes, a keyway or dowel
can be used as a timing mark. If needed, refer to the service
manual. These sprocket markings must be pointing in the
correct direction to time the camshaft and valves with the
crankshaft and pistons.
1. Install the sprockets without the chain, Figure 23-5.
2. Turn the camshaft and crankshaft so that their timing
marks align.
3. Remove the sprockets without turning the camshaft or
crankshaft.
4. Fit the timing chain over the sprockets. The timing
marks should align.
5. Fit the sprockets and chain onto the engine with the
camshaft and crankshaft in correct timing, Figure 23-6.
6. If so equipped, mount the fuel pump eccentric on
the camshaft sprocket. Usually, the camshaft dowel
fits through a hole in the eccentric and the camshaft
sprocket bolt passes through the eccentric center.