Table of Contents
Advertisement
8-8
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 the vacuum enough
to indicate that the trouble has been
corrected. It is important, therefore,
that each cause of an abnormal read-
ing be investigated and further tests
be conducted where necessary in
order to arrive at the correct diag-
nosis of the trouble.
Table 1 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.
GROUP 8-ENGINE
and choke plate in the wide open
position.
4. Install a compression gauge in
No. 1 cylinder.
5. Using
an
auxiliary
starter
switch, crank the engine a minimum
of five pumping strokes and record
the highest reading. On engines
equipped with transistor ignition,
refer to Group 9 for the procedure
on installing an auxiliary starter
switch. Note the number of com-
pression strokes required to obtain
the highest reading.
6. 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
TABLE
1-Manifold Vacuum Gauge Readings
Gauge Reading
Engine Condition
18 inches or over
Normal.
Low and steady.
Loss of power in all cylinders caused pos-
sibly by late ignition or valve timing, or loss
of compression due to leakage around the
piston rings.
Very low.
Manifold, carburetor, spacer or cylinder
head gasket leak.
I
Needle fluctuates steadily
A partial or complete loss of power in one
as speed increases.
or more cylinders caused by a leaking valve,
cylinder head or intake manifold gasket
leak, a defect in the ignition system or a
weak valve spring.
Gradual drop in reading at
Excessive back pressure in the exhaust
engine idle.
system.
Intermittent fluctuation.
An occasional loss of power possibly caused
by a defect in the ignition system or a
sticking valve.
Slow fluctuation or drift-
Improper idle mixture adjustment or carbure-
ing of the needle.
tor, spacer or intake manifold gasket leak.
COMPRESSION TEST
1. Be sure the crankcase oil is at
the proper level.
satisfactory. However, the compres-
sion of all cylinders should be uni-
form within 10 psi.
A reading of more than the allow-
able tolerance above normal indi-
cates excessive deposits in the cyl-
inder.
2. Be sure the battery is properly
charged. Operate the engine for a
minimum of 30 minutes at 1200 rpm
or until the engine is at normal oper-
ating temperature. Turn the ignition
switch off, then remove all the spark
plugs. Remove the coil high tension
lead from the distributor cap and
coil.
3. Set the primary throttle plates
A reading of more than the allow-
able tolerance below normal indi-
cates leakage at the cylinder head
gasket, piston rings or valves.
A low, even compression in two
adjacent cylinders indicates a cylin-
der head gasket leak. This should be
(128)
checked before condemning the rings
or valves.
To 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 leak-
ing. If the compression has increased
10 pounds or more over the original
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 succeeding strokes, or fails to
climb during the entire test, it indi-
cates a sticking valve.
HYDRAULIC VALVE
LIFTER TESTS
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 reservoir 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 lub-
ricating system through an opening
in a damaged oil pick-up tube. Air
in the hydraulic system can oause
a loss of hydraulic pressure.
Assembled valve lifters can be
tested with tool-6500-E to check the
leak down rate. The leak down rate
specification (for gauging purposes)
is 10-100 seconds at 50 lbs. load.
Plunger travel is 0.125 inch. Test the
valve lifters as follows:
1. Place the valve lifter in the
tester, with the plunger facing up-
ward. Pour hydraulic tester fluid into
the cup to a level that will cover
the valve lifter assembly. The fluid
can he purchased from the manu-
facturer of the tester. Do not use
kerosene, for it will not provide
an accurate test.
2. Place a
~lia-inch
steel hall in
the plunger cup (Fig. 2).
3. Adjust the length of the ram
Advertisement
Table of Contents
Troubleshooting
