2. Remove the spark plugs as described in this
chapter.
3. Insert each spark plug into its spark plug cap,
and ground the spark plug against the cylinder head
(
Figure 7
).
4. Turn the compression gauge into one cylinder
following the manufacturer’s instructions (
Figure
8
). Make sure the gauge is properly seated in the
cylinder head.
5. Completely open the throttle, and crank the en-
gine until there is no further rise in pressure. Re-
move the gauge and record the reading.
6. Repeat Steps 3-5 for the other cylinder.
7. Standard compression pressure is specified in
Table 5
. When interpreting the results, note the dif-
ference between the cylinders. Large differences in-
dicate worn or broken rings, leaky or sticky valves,
blown head gasket or a combination of all.
a. If the compression reading between cylinders
does not differ by more than 10%, the rings
and valves are in good condition.
b. If the reading is low (10% or more) on one of
the cylinders, it indicates valve or ring trou-
ble.
c. To determine which, pour about a teaspoon of
engine oil through the spark plug hole onto
the top of the piston. Turn the engine over
once to distribute the oil, then take another
compression test and record the reading. If
the compression returns to normal, the rings
are worn or defective. If compression does
not increase, the valves are leaking.
NOTE
If the compression is low, the engine
cannot be tuned to maximum perfor
mance. The worn parts must be re
placed.
Ignition Timing
Ignition timing is not adjustable. However, the
timing can be checked to make sure all ignition
components are operating correctly.
1. Start the engine and let it reach normal operating
temperature. Shut the engine off.
2. Remove the timing inspection cover (A,
Figure
9
) from the alternator cover.
3. Connect a portable tachometer following the
manufacturer’s instructions.
4. Connect a timing light to the No. 1 spark plug
wire (rear cylinder) following the manufacturer’s
instructions.
5. Start the engine and let it idle at the idle speed
listed in
Table 5
.
6. Aim the timing light at the timing window. The
timing is correct if the timing mark (A,
Figure 10
)
on the flywheel aligns with the cutout in the timing
window (B).
7. If the timing is incorrect, there is a problem in
the ignition system. Follow the ignition system
troubleshooting procedures listed in Chapter Two.
The ignition timing cannot be adjusted.
LUBRICATION, MAINTENANCE AND TUNE-UP
59
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9