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Section 4 Engine Service
If the engine being serviced is an L-head engine,
the cylinder head installation is complete. If the
engine is an overhead valve engine, the pushrods
and rocker arms must be installed and valve clear-
ance must be checked and adjusted if needed.
Installing Pushrods and Rocker Arms
Place the pushrods into their respective guides.
Place the rocker arms on the studs and install the
rocker arm nuts. Turn the nuts until they just touch
the rocker arms. Carefully rotate the crankshaft to
verify proper pushrod operation.
Adjusting Overhead Valve Clearance
Proper clearance between the rocker arm and
the valve stem is essential. Too much clearance
will reduce volumetric effi ciency. Too little clear-
ance can cause valve burning or warpage.
Before checking valve clearance, position the
piston as recommended by the manufacturer. To
accomplish this, simply rotate the crankshaft until
the piston reaches the position specifi ed. Top Dead
Center is the correct piston position for some engines;
others may require the piston to be a certain distance
beyond Top Dead Center. Always check specifi ca-
tions. If necessary, the distance past Top Dead Center
can be measured through the spark plug hole with a
ruler, dial indicator, or similar tool.
Once the piston is set at the correct position,
place the proper feeler gauge leaf between the
rocker arm and the valve stem. See Figure 19-23.
Check engine specifi cations for the required clear-
ance. Some engines require equal clearance for
both intake and exhaust valves. However, some
engine manufacturers use a different metal for
exhaust valves than intake valves, so the coeffi -
cient of thermal expansion is not the same for each
valve. Therefore, clearances must be different for
each valve.
Turn the locking/adjusting nut clockwise to
reduce clearance or counterclockwise to increase
clearance. The feeler gauge should drag slightly
when pulled out. Hold the adjusting nut with a
wrench and tighten the locking screw slightly.
Recheck clearance with the feeler gauge. If neces-
sary, readjust until correct clearance is obtained.
Tighten the locking screw.
Installing the Crankcase
Breather and Valve Cover
If an L-head engine is being reassembled,
make sure the oil drain back holes are clear, and
then bolt the crankcase breather assembly in place.
If there is a breather passage cast into the block,
replace the cover on the passage as well.
If an overhead valve engine is being reassem-
bled, replace the crankcase breather, valve cover,
and gaskets. See Figure 19-24. Tighten the valve
cover bolts to the recommended torque setting.
See Figure 19-25.
Figure 19-23.
Adjust rocker arm-to-valve stem clearance until very
slight drag is felt on the thickness gauge.
(Briggs & Stratton Corp.)
Thickness
gauge
Figure 19-24.
When a valve cover and breather assembly is
installed, all mating surfaces should be clean and new
gaskets should be used. (Briggs & Stratton Corp.)
Gasket
Breather
Gasket
Valve cover