262
Section 4 Engine Service
Summary
Preventive maintenance involves tasks that
must be performed regularly to keep an engine
working properly. Cleaning a small air-cooled
engine periodically can help prevent overheating.
For proper cooling action, air must pass across
the metal surfaces of the cylinder block and cyl-
inder head. If the cooling fi ns are insulated by
dirt, leaves, and/or grass clippings, engine parts
will retain most of the combustion heat. Parts will
expand, probably distort, and possibly seize.
Crankcase oil in four-cycle engines should
be checked periodically. The small engine manu-
facturer will recommend oil changes at intervals
based on hours of running time. The time speci-
fi ed may vary from 10–50 hours.
Engine cables and linkage should be lubricated
periodically to ensure smooth operation and re-
duce the chances of binding and premature wear.
Many manufacturers recommend silicone-based
lubricants for use on cables and linkages. Unlike
petroleum-based products, these lubricants will
not attract dirt after they are applied.
The spark plug should periodically be removed
for inspection and cleaned or replaced. Carefully
examine the electrode end of the plug. An insula-
tor or electrodes that are wet with fuel or oil may
be a sign of serious engine problems. If the spark
plug insulator and electrodes appear to be good,
the plug can be reinstalled. Examine the spark
plug wire for deterioration before reinstalling it on
the spark plug. Heat and dirt can make the insula-
tion brittle and insulation cracking can occur.
The air cleaner should be cleaned before each
season of operation and at regular intervals there-
after. A plugged air fi lter can cause hard starting,
loss of power, and spark plug fouling. The three
types of air cleaners widely used in small gasoline
engines are the oil-wetted type, the dry type, and
the dual-element type. Each has a different meth-
od of cleaning and servicing.
If the small gasoline engine has a crankcase
breather, the breather assembly should be removed
and cleaned periodically. The breather is located
over the valve stem chamber.
A muffl er is designed to reduce noise and allow
exhaust gases to escape. When it becomes clogged,
gases cannot get out of the combustion chamber
quickly enough to allow fresh air and fuel to enter.
This causes a loss in engine power, along with a
tendency to overheat.
The battery in a small engine–powered imple-
ment may be either a maintenance-free or a con-
ventional lead-acid battery. Conventional lead-acid
batteries need occasional additions of distilled wa-
ter to keep the electrolyte level above the plates.
Fill to the level shown on the case of the battery.
Corrosion at the battery terminals and cable con-
nectors is not uncommon. The corrosion should be
cleaned from the terminals.
The pressurized liquid cooling systems used
in small engines require maintenance similar to
that employed in the automobile engine. Because
the combination of water and metal sometimes
produces harmful chemical reactions that attack
the water jacket, antifreeze containing a chemical
rust inhibitor should be added whenever a system
is drained and refi lled. Outboard engine cooling
systems can be clogged with dirt, sand, or other
debris. Flushing the internal cooling system of an
outboard engine is extremely important.
Several precautions should be taken when
storing an air-cooled engine. Proper storage pro-
cedures will help ensure long engine life and
easy starting the following season. Storing liquid-
cooled engines for lengthy periods calls for special
maintenance procedures. If the engine has a pres-
surized system, the coolant must be strong enough
to protect against freezing at the lowest possible
temperatures.
If the engine will not start, is hard to start, runs
rough, or lacks power, troubleshooting may be
necessary. Troubleshooting is simply a number of
tests and steps you go through to fi nd a problem.
In order to start and run properly, an engine must
meet fi ve fundamental operating requirements.
These requirements include proper carburetion,
correct ignition system operation, adequate lubri-
cation, suffi cient cooling, and proper compression.
A cylinder compression test can be a fi rst step
toward determining the condition of the upper
major mechanical parts of the engine. This test is
especially valuable if an engine lacks power, runs
poorly, and shows little or no improvement after
fuel system and ignition adjustments. A differen-
tial pressure test checks the condition of an engine
by measuring leakage from the cylinder to other
parts of the engine. This test device and procedure
can identify a specifi c worn or damaged compo-
nent in the engine that may or may not be directly
related to the cylinder condition or rings.