Ford COUGAR 1968 Shop Manual page 288

GROUP 8
-
Engine
valves, cylinder compression, the con-
dition of the closed crankcase ven-
tilation system, and leakage of the
manifold, carburetor, carburetor spacer
or cylinder head gaskets.
Because abnormal gauge readings
may indicate that more than one of
the above factors are at fault, exer-
cise caution in analyzing an abnor-
mal reading. For example, if the
vacuum is low, the correction of one
item may increase t h e vacuum
enough so as to indicate that the
trouble has been corrected. It' is im-
portant, therefore, that each cause
of an abnormal reading be investi-
gated and further tests conducted,
where necessary, in order to arrive at
the correct diagnosis of the trouble.
Fig. 4 lists various types of read-
ings and their possible causes.
Allowance should be made for the
effect of altitude on the gauge read-
ing. The engine vacuum will decrease
with an increase in altitude.
COMPRESSION TEST
Dynamic Compression Test
To perform a dynamic compres-
sion check, follow the procedures in
Part 9-1, Section 1 under Ignition
System Tests-Rotunda Testers.
Compression G a u g e Check
1. Be sure the crankcase oil is at
the proper level. Be sure the battery
is fully charged. Operate the engine
for a minimum of 30 minutes at 1200
rpm or until the engine is at normal
operating temperature. Turn the' igni-
tion switch .off, then remove all the
spark plugs.
2. Set the throttle plates (primary
throttle plates only on a 4-barrel
carburetor) and choke plate in the
wide open position.
3. Install a compression gauge in
No. I cylinder.
4. Disconnect the brown lead ( I
terminal) and the red and blue lead
( S terminal) at the starter relay. In-
stall an auxiliary starter switch between
the battery and S terminals of the
starter relay. Using an auxiliary starter
switch, crank the engine (with the ig-
nition switch off) at least five pumping
strokes, and record the highest reading.
Note the number of compression
strokes required to obtain the highest
reading.
5. Repeat the test on each cylin-
der, cranking the engine the same
number of times for each cylinder as
was required to obtain the highest
reading on the No. 1 cylinder.
Test Conclusions
A variation of 20 psi from specified
pressure is satisfactory. However, the
compression of all cylinders should be
uniform within 20 psi.
A reading of more than the allow-
able tolerance above normal indi-
cates excessive deposits in the cyl-
inder or wrong cylinder head(s) on
the engine.
A reading of more than the allow-
able tolerance below normal indi-
cates leakage at the cylinder head
gasket, piston rings or valves or
wrong cylinder head(s) on the engine.
A low, even compression in two
adjacent cylinders indicates a cylin-
der head gasket leak. This should be
checked before condemming the rings
or valves.
T o determine whether the rings or
the valves are at fault, squirt the
equivalent of' a tablespoon of heavy
oil into the combustion chamber.
Crank the engine to distribute the
oil and repeat the compression test.
The oil will temporarily seal leakage
past the rings. If approximately the
same reading is obtained, the rings
are satisfactory, but the valves are
leaking. If the compression has in-
creased substantially over the orig-
inal reading, there is leakage past the
rings.
During a compression test, if the
pressure fails to climb steadily and
remains the same during the first
two successive strokes, but climbs
higher on the succeding strokes, or
fails to climb during the entire test,
it indicates a sticking valve.
H Y D R A U L I C VALVE
LIFTER TESTS
Hydraulic valve lifter noise may be
caused by improper operating clear-
ance as a result of loose adjusting nuts
or improper original adjustment. Al-
ways check rocker arm to valve stem
clearance before condemning or re-
placing a valve lifter.
Dirt, deposits of gum and varnish
and air bubbles in the lubricating oil
can cause hydraulic valve lifter failure
or malfunction.
Dirt, gum and varnish can keep
a check valve from seating and cause
a loss of hydraulic pressure. An open
valve disc will cause the plunger to
Force oil back into the valve lifter res-
ervoir during the time the push rod is
being lifted to force the valve from its
seat.
Air bubbles in the lubricating sys-
tem can be caused by too much oil in
the system or too low an oil level. Air
may also be drawn into the lubricating
system through an opening in a dam-
aged oil pick-up tube. Air in the hy-
draulic system will cause a loss of hy-
draulic pressure in the valve lifter.
Assembled valve lifters can be
tested with tool 6500-E to check the
leak down rate. The leak down rate
specification (Part 8-5) is the time
in seconds for the plunger to move
the length of its travel while under a
50 Ib. load. Test the valve lifters as
follows:
1. Disassemble and clean the lift-
,
er to remove all traces of engine oil.
Lifters cannot be checked with engine
oil in them. Only the testing fluid can
be used.
2.
Place the valve lifter in the
tester, with the plunger facing upward.
Pour hydraulic tester fluid into the
cup to a level that will cover the valve
lifter assembly. 'The fluid can be pur-
chased from the manufacturer of the
tester. Do not use kerosene or any
other fluid, for they will not provide
an accurate test.
A 1 894-A
FIG. 5-
Placing Steel
Ball
in Valve
Lifter Plunger
3. Place a 5116-inch steel ball in
the plunger cup (Fig. 5).
4. Adjust the length of the ram so
that the pointer is 1116-inch below the
starting mark when the ram contacts
the valve lifter plunger (Fig. 6) to
facilitate timing as the pointer passes
the Start Timing Mark.
Use the center mark on the point-
er scale as the $top Timing point
instead of the original Stop Timing
mark at the top of the scale.
5. Work the valve lifter plunger
up and down until the lifter fills
with fluid and all traces of air bubbles
have disappeared.
6. Allow the ram and weight to
force the valve lifter plunger down-
ward. Measure the exact time it takes
for the pointer to travel from the
Start Timing to the Stop Timing
marks of the tester.
7. A valve lifter that is satisfactory