Small Gas Engines, 10th Edition Page 365 (365 of 528)

365
Chapter 19 Engine Reassembly and Break-In
Place the cylinder head on a workbench and
support the valve faces with wooden blocks. If
stem seals are used, place them over the stems.
Place the valve springs over the valve stems and
set the retainers on the springs. Compress the
springs and install the retainers. See Figure 19-20.
Installing the Cylinder Head
The mating surfaces of the cylinder and the cyl-
inder head should be completely clean. Install a new
head gasket on the cylinder block and then align
and place the cylinder head on the cylinder. See
Figure 19-21. Never use gasket cement or sealer on
a head gasket. Install the bolts through the head and
into the cylinder block holes. Do not apply oil or anti-
seize compound to the bolts unless specifi cally rec-
ommended by the manufacturer’s service manual.
Tighten the bolts evenly by hand in a criss-
cross pattern. Then, use a torque wrench to tighten
the bolts to the proper torque specifi cations. See
Figure 19-22. Torque the head bolts in sequential
increments in the pattern specifi ed by the manu-
facturer to avoid causing the cylinder head to warp.
Figure 19-20.
Valves must be installed in an overhead valve cylinder head before the head is installed on the engine. A—Installing
valve spring retainers. B—Replacing split-type retainers. A magnetized screwdriver or a bit of grease helps to place
the retainer onto the valve stem recess. (Briggs & Stratton Corp.)
A B
Valve stem
Retainer
Retainer
Valve spring
compressor
Figure 19-21.
Use a new gasket when installing the cylinder head
on the block. Head and block surfaces must be clean.
(Briggs & Stratton Corp.)
Cylinder
Cylinder
head Gasket
Figure 19-22.
Tighten the cylinder head bolts with a torque wrench
in the proper sequence and in gradual increments to
avoid head warpage.
Pushrods
1 4
2
5
3

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365
Chapter 19 Engine Reassembly and Break-In
Place the cylinder head on a workbench and
support the valve faces with wooden blocks. If
stem seals are used, place them over the stems.
Place the valve springs over the valve stems and
set the retainers on the springs. Compress the
springs and install the retainers. See Figure 19-20.
Installing the Cylinder Head
The mating surfaces of the cylinder and the cyl-
inder head should be completely clean. Install a new
head gasket on the cylinder block and then align
and place the cylinder head on the cylinder. See
Figure 19-21. Never use gasket cement or sealer on
a head gasket. Install the bolts through the head and
into the cylinder block holes. Do not apply oil or anti-
seize compound to the bolts unless specifi cally rec-
ommended by the manufacturer’s service manual.
Tighten the bolts evenly by hand in a criss-
cross pattern. Then, use a torque wrench to tighten
the bolts to the proper torque specifi cations. See
Figure 19-22. Torque the head bolts in sequential
increments in the pattern specifi ed by the manu-
facturer to avoid causing the cylinder head to warp.
Figure 19-20.
Valves must be installed in an overhead valve cylinder head before the head is installed on the engine. A—Installing
valve spring retainers. B—Replacing split-type retainers. A magnetized screwdriver or a bit of grease helps to place
the retainer onto the valve stem recess. (Briggs & Stratton Corp.)
A B
Valve stem
Retainer
Retainer
Valve spring
compressor
Figure 19-21.
Use a new gasket when installing the cylinder head
on the block. Head and block surfaces must be clean.
(Briggs & Stratton Corp.)
Cylinder
Cylinder
head Gasket
Figure 19-22.
Tighten the cylinder head bolts with a torque wrench
in the proper sequence and in gradual increments to
avoid head warpage.
Pushrods
1 4
2
5
3

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364
Section 4 Engine Service
Caps must never be switched from one rod to another.er.thano
Frequently, locking devices are installed on the
rod cap to stop connecting rod bolts or cap screws
from loosening in service. One common device
is a thin sheet metal strip with locking tabs. See
Figure 19-19. The cap screw is inserted through
holes in the locking strip, holding it in place against
the rod. After the cap screw is tight, the metal tabs
are bent up against the fl at sides of the screw head.
Self-locking nuts, lock washers, and specially
shaped cap screws are also used to prevent loosen-
ing. The fi nal tightening of the cap screws is espe-
cially important. Always use a torque wrench to
tighten rod fasteners to the exact torque specifi ed
by the manufacturer.
Installing Overhead Valves
Before starting assembly of an overhead valve
cylinder head, inspect valve stems for foreign
material and burrs, which can cause sticking and
damage the new stem seals. Coat the valve stems
with valve guide lubricant. Do not allow the lubri-
cant to contact the valve face, valve seat, or end
of the valve stem. Install the valves in the cylin-
der head, being careful to install the intake and
exhaust valves in their respective guides.
Caution
Caps C Ca a p s must m m us never ne e be e switched i f rom one ro d t o C C C t b i i t h d f d t th
Figure 19-17.
Lubricate the connecting rod bearing surfaces and
the crankshaft journals with assembly lube before
installing the rod cap. A—Assembly lube being applied
to rod cap. B—Rod cap installed on rod.
A
B
Figure 19-18.
Connecting rod cap installation. A—If the cap is turned
180°, the rod bore will be offset. B—The match marks
on the rod and cap signal correct assembly.
A B
Incorrect
correct
Cap
reversed
Match
marks
Figure 19-19.
A locking plate is often used between the connecting
rod cap and cap screws. (Tecumseh Products Co.)
Match marks
Locking plate

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366
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

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Page 14Section 1 Shop Equipment, Supplies, and Safety click to expand contents

Page 94Section 2 Basics of Engine Operation click to expand contents

Page 152Section 3 Engine Systems click to expand contents

Page 242Section 4 Engine Service click to expand contents

Page 372Section 5 Applications click to expand contents

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