
TROUBLESHOOTING
53
DETONATION
Very rapid combustion
Early expansion causes
knock
TDC
Little expansion after
TDC
results in power
loss
Excessive
Vibrations
Excessive vibrations may be caused by loose engine,
suspension or steering mount bolts.
Engine Noises
A change in the sound of the engine is often the first
clue that an engine problem exists. Noises are difficult to
differentiate and even harder to describe. Experience is
needed to accurately diagnose problems using engine
sounds
(Figure
26).
TWO-STROKE PRESSURE TESTING
Hard to start and generally poor performing two-stroke
engine may be caused by leaking crankcase compression.
Fuel delivery and ignition systems may be good, and a
compression test may indicate that the engine's upper end
is in good condition but a conventional compression test
does not show a lack of primary (crankcase) compression.
In a two-stroke engine, the crankcase must be alternately
under pressure and vacuum. After the piston closes the in-
take port, further downward movement of the piston
causes the trapped mixture to be pressurized so it can rush
quickly into the cylinder when the scavenging ports are
opened. Upward piston movement lowers the pressure
creates a vacuum) in the crankcase, drawing the air-fuel
mixture in from the carburetor.
NOTE
The operational sequence of a two-stroke
engine is illustrated in Chapter One.
If crankcase seals or cylinder base gaskets leak, the
crankcase cannot hold either pressure or vacuum and
proper engine operation is impossible. Any other source
of leakage such as porous or cracked crankcase castings
results in the same conditions.
It is possible to test for and isolate engine crankcase
leaks. The test is simple but requires special equipment. A
typical two-stroke pressure test kit is shown in
Figure 27.
Pressure testing requires plugging all engine openings,
then applying air pressure. If the engine does not hold air,
a leak is present that must be located and repaired.
The following procedure describes a typical pressure
test.
NOTE
The labyrinth seal at the center o f the crank-
shaft
prevents the cylinders from being
checked individually. When one cylinder is
pressurized, the other
are also
pressurized. All cylinders must be
before applying pressure during testing.
1.
Remove the carburetors as described
in Chapter Five.
2. Insert a plug tightly in the intake manifold.
3.
Remove the exhaust pipes and block off the exhaust
ports, using suitable adapters and fittings.
4.
Remove one spark plug and install the pressure gauge
adaptor into the spark plug hole. Connect the pressurizing
lever and gauge to the installed adapter, then squeeze the
lever until the gauge indicates approximately
9 psi.
5.
Observe the pressure gauge. If the engine is in good
condition, the pressure should not drop more than 1
to
2 psi in several minutes. Any pressure loss of 1 psi in one
minute indicates serious sealing problems.
6.
Before condemning the engine, first make sure there
are no leaks in the test equipment or
plugs. If the
equipment shows no leakage, go over the entire engine
carefully. Large leaks can be heard. Smaller leaks can be
found by going over every possible leakage source with a
Содержание MM600D
Страница 5: ......
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Страница 104: ...98 CHAPTER FOUR ENGINE MOUNTS ...
Страница 137: ...FUEL AND EXHAUSTSYSTEMS 131 ...
Страница 144: ...138 CHAPTER FIVE CARBURETOR HEATER SYSTEM Carburetorheater control valve ...
Страница 211: ...BRAKES 205 Wear limit ...
Страница 226: ...220 CHAPTER TWELVE ...
Страница 228: ...222 CHAPTER TWELVE ...
Страница 229: ...CHAINCASE JACKSHAFTAND FRONT AXLE 223 ...
Страница 230: ...224 CHAPTER TWELVE ...
Страница 254: ...248 CHAPTER THIRTEEN FORWARD Negative Positive O0Camber Angle finder ...
Страница 266: ...260 CHAPTERFOURTEEN FRONT Track I Ground fevel OBSTRUCTION DAMAGE 0 LUG DAMAGE 0 RATCHETING DAMAGE ...
Страница 277: ...1 Wiring Diagrams ...
Страница 282: ...NOTES ...