Ford Thunderbird Manual page 15

03-oo-14
SERVICE PROCEDURES (Continued)
7. NOTE: If lift on any lobe is below specified service
limits, camshaft and valve tappet operating on
worn lobes must be replaced, as well as any
valve tappet showing roller wear or needle
bearing damage (3.8L). Refer to Service
Procedures.
Compare total lift recorded on indicator with
specifications.
To check accuracy of original indicator reading,
8.
continue to rotate crankshaft until indicator reads
zero.
9. Remove dial indicator, adapter and auxiliary
starter switch.
10. CAUTION: After installing rocker arms, do
not rotate crankshaft until valve tappets
have had sufficient time to bleed down. To
do otherwise may cause serious valve
damage. Manually bleeding-down valve
tappets will reduce waiting time.
Install rocker arm seats, rocker arms and rocker
arm seat bolts.
11. Install valve covers.
12. Install spark plugs.
Hydraulic Valve Tappet
Hydraulic valve tappet noise may be caused by any of
the following:
• excessive collapsed valve tappet gap
•
sticking valve tappet plunger
• valve tappet check valve not functioning properly
•
air in lubrication system
•
leakdown rate too rapid
• excessive valve guide wear
Excessive collapsed valve tappet gap may be caused
by loose rocker arm seat bolts I nuts, incorrect initial
adjustment or wear of valve tappet face, or worn roller
valve tappets, push rod, rocker arm, rocker arm seat
or valve tip. With valve tappet collapsed, check gap
between valve tip and rocker arm to determine if any
other valve train parts are damaged, worn or out of
adjustment.
A sticking valve tappet plunger may be caused by dirt,
chips or varnish inside the valve tappet. The sticking
can be corrected by disassembling the valve tappet
and removing the dirt, chips or varnish that are
causing the condition.
A valve tappet check valve that is not functioning may
be caused by an obstruction such as dirt or chips that
prevent it from closing when the camshaft lobe is lifting
the valve tappet. It may also be caused by a broken
check valve spring.
Air bubbles in the lubrication system will prevent the
valve tappet from supporting the valve spring load.
This may be caused by too high or too low an oil level
in the oil pan (6675) or by air being drawn into the
system through a hole, crack or leaking gasket on the
oil pump screen cover and tube (6622).
Engine-Service
If the leakdown time is below the specified time for
used valve tappets, noisy operation may result. If no
other cause for noisy valve tappets can be found, the
leakdown rate should be checked and any valve
tappets outside the specification should be replaced.
Assembled valve tappets can be tested with a
hydraulic tappet leakdown tester to check the
leakdown rate. The leakdown rate specification is the
time in seconds for the plunger to move a specified
distance while under a 22.7 kg (50 lb) load. Test the
valve tappets as follows.
Leakdown Testing
1. NOTE: Do not mix parts from different valve
tappets. Parts are select-fit and not
interchangeable.
Disassemble and clean valve tappet to remove all
traces of engine oil.
2. NOTE: Valve tappets cannot be checked with
engine oil in them. Use only testing fluid.
Place valve tappet in tester with plunger facing
upward. Pour hydraulic tester fluid into cup to a
level that will cover valve tappet. The fluid can be
purchased from the tester's manufacturer. Using
kerosene or any other fluid will not provide an
accurate test.
3. Place a 7.94 mm (0.312-inch) steel ball provided
with tester in plunger cap.
4. Adjust length of ram so that pointer is 1.59 mm
(0.062 inch) below starting mark when ram
contracts tappet plunger to facilitate timing as
pointer passes Start Timing mark.
Use center mark on pointer scale as Stop Timing
point instead of original Stop Timing mark at top
of scale.
Work valve tappet plunger up and down until
5.
valve tappet fills with fluid and all traces of air
bubbles have disappeared.
6. Allow ram and weight to force valve tappet
plunger downward. Measure exact time it takes
for pointer to travel from Start Timing to Stop
Timing marks of tester.
7. A satisfactory valve tappet must have a
leakdown rate (time in seconds) within specified
minimum and maximum limits as described under
Specifications in Section 03-01 A (3.8L) or
Section 03-Q18 (4.6L).
If valve tappet is not within specification, replace
8.
it with a new valve tappet. Do not disassemble
and clean new valve tappets before testing
because oil contained in new valve tappets is test
fluid.
9. Remove fluid from cup and bleed fluid from valve
tappet by working plunger up and down. This step
will aid in depressing valve tappet plungers when
checking valve clearance.
03-0Q- 14
1 997 Thunderbird, Cougar July 1 996