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Section 4 Engine Service
Install the ignition module, set the proper air
gap, and then tighten the mounting bolts. Then,
install any brackets or shrouds on the engine.
Reinstall the intake manifold, carburetor, and air
fi lter assembly, using new gaskets. Make sure the
breather hose is reconnected to the air fi lter or car-
buretor intake.
Reinstall the governor linkages. Refer to
sketches or photos taken during engine disassem-
bly to ensure that the governor linkages are reas-
sembled properly. Make sure there is no binding
by operating the governor linkages by hand.
Install any remaining engine components,
including oil fi ller tube, throttle and choke link-
ages, gas tank, starter, muffl er, and drive pulley.
Install a new fuel line and fi lter. Refi ll the engine
with the required amount of fresh motor oil and
make sure there is fresh gasoline in the tank. The
fi nal step in engine reassembly is to gap and install
a new spark plug. The spark plug wire should not
be attached to the spark plug until you are ready to
start the engine. This will prevent the engine from
fi ring accidentally.
Engine Break-In
Secure the engine on a test stand or reinstall it
on the implement before starting it for the fi rst time.
Although some engines can be bench tested, push
lawn mower engines are often equipped with a
lightweight fl ywheel, and require the added mass
of a mower blade to operate properly. These engines
should be remounted on the mower and the blade
should be reinstalled before the engine is started.
Before starting the engine, check for and fi x any
fuel or oil leaks. Several attempts may be required to
start the engine for the fi rst time. Be prepared to stop
the engine quickly if the governor malfunctions or if
there are any indications of severe engine problems.
After starting the engine and letting it warm to oper-
ating temperature, make any necessary carburetor
and governor adjustments. The engine may smoke
excessively when fi rst started. The smoking should
diminish as the oil applied to the piston and rings
burns away and the rings are broken-in.
After a reconditioned engine is started, a short
break-in period occurs. Break-in is the process in
which the face of each ring wears off until it fi ts per-
fectly against the cylinder wall. To help the rings
seat quickly, the face is covered with microscopic
grooves. During the fi rst few hours of operation,
these grooves rub against the cylinder wall and all
high spots are worn off. As the grooves wear away,
the faces of rings and the cylinder wall become
very smooth. Under normal operating conditions,
very little wear occurs beyond this point.
Ring break-in varies from engine to engine, but
may take as many as ten hours of operation. During
this period, the engine oil level should be checked
frequently. The engine oil should be changed after
the fi rst hour of operation. The greatest wear occurs
during this period, and changing the oil removes
the metal particles resulting from the wear. The
engine can be operated normally during the break-
in period, but should not be subjected to heavy
loads until the break-in period is over.
Some manufacturer’s require the cylinder head
to be retorqued after a certain number of hours of
operation. Additional service measures may be
required during or following the break-in period.
Always consult the manufacturer’s service manual
for proper break-in procedures.
Figure 19-27.
If a Woodruff key is used on a crankshaft, it should
be placed so that the top of the key is parallel to the
centerline of the crankshaft.