TM 5-4930-227-14
CHAPTER 6
REPAIR INSTRUCTIONS
Section I. ENGINE COMPONENTS
6-1. General
a. Cylinder Head. The cylinder head covers the
top of the cylinder and provides a mounting port
for the spark plug. It is finned to help dissipate
the heat of engine combustion.
b. Valve Tappets. Intake and exhaust valves
have tappets which raise the valves at the re-
quired portion of the engine operation cycle.
These tappets operate in conjunction with the
camshaft. Valve tappet clearance can be checked
without major engine disassembly, but it cannot
be adjusted without disassembly.
6-2. Cylinder Head
a. Removal.
(1) Remove the spark plug (para 3-23).
(2) Remove the air shroud (para 3-20).
(3) Refer to figure 6-1 and remove the
cylinder head and gasket.
b. Cleaning and Inspection.
(1) Discard the cylinder head gasket. Clean
the cylinder head and cylinder head bolts with
an approved cleaning solvent; scrape carbon de-
posits from the cylinder head, taking care not to
scratch sealing surfaces.
(2) When the cylinder head is removed,
clean the top of the cylinder block, carefully re-
moving carbon from piston tops and from around
the valve head and seats. Take care not to scratch
or score valve seats.
(3) Inspect the cylinder head for cracks,
warping, broken cooling fins, spark plug port
threads, and other damage. Straighten bent cool-
ing fins. Replace a damaged cylinder head.
c. Installation.
(1) Refer to figure 6-1 and install the cylin-
der head, using a new gasket.
(2) Install the air shroud (para 3-20).
(3) Install the spark plug (para 3-23).
(4) After installation of air shroud, torque
all cylinder head mounting bolts, following the
sequence shown in figure 6-2.
6-3. Tappet Cover Plate and Tappets
a. Removal. Refer to figure 6-3 and remove
the tappet cover plate.
b. Cleaning and Inspection.
(1) Clean the cover plate and accessible
metal parts with an approved cleaning solvent
and dry thoroughly.
(2) Measure valve clearance (fig. 6-3) and
inspect for defective valve springs, tappets, rota-
tors, and seats.
c. Installation. Refer to figure 6-3 and install
the tappet cover plate.
6-4. Valves, Valve Seats, Guides, and Springs
a. Removal.
(1) Remove the engine (para 3-17).
(2) Remove the carburetor (para 3-28).
(3) Remove the muffler (para 3-31).
(4) Remove the cylinder head (para 6-2).
(5) Remove the tappet cover plate (para 6-
3).
b. Disassembly. Refer to figure 6-4 and disas-
semble the valves, valve seats, guides and springs.
c. Cleaning, Inspection, and Repair.
(1) Clean the valves with a wire brush to
remove all carbon deposits. Clean valve seats,
ports, and guides in cylinder block; clean top of
cylinder block. Wash springs with an approved
cleaning solvent and dry thoroughly.
(2) Inspect valves for burned, pitted, or
cracked faces; replace a burned, cracked, or deep-
ly pitted valve.
(3) Inspect valve springs for cracks or pit-
ting. Replace cracked or pitted springs.
(4) Inspect valve seat insert for looseness
and pitting. Replace a defective valve seat insert
in the following manner:
(a) Use a puller to remove the insert from
the exhaust valve opening.
(b) Clean all carbon out of the insert
counterbore in the cylinder block and clean the
valve stem guide bore.
6-1