Hitachi EX20UR-2 Manual page 339

ENGINE/Engine
VALVE, VALVE SEAT INSERT
AND VALVE SEAL
Cylinder head
Valve
45° (Common to inlet and exhaust)
Valve must not extrude from bottom
face of cylinder head.
Valve seat
(1) Contact width: Inspection A
(2) Sink amount: Inspection B
(mm)
Standard Limit Repair method
Contact width: A 1.75 2.5
Repair or replace
valve and insert.
Sink amount: B 3.2 3.7
G 0.7 1.4
Valve seat insert
Press in the insert using a soft plate with a care not to
damage the insert surface. (4000 kg)
Notes in removing valve seat insert
(1) Heat the inside of valve seat insert at diagonal two
places using a gas burner. (700 — 800°C)
(2) Allow it in the air for 3 to 5 minutes to cool, then
remove the insert by hitting lightly the cylinder head
with a care not to damage the cylinder head.
Valve seal
Note 1: Press in the seal until it gets stuck against the
top face of cylinder head.
Note 2: Apply oil to the outer surface of valve guide
when pressing in the seal.
Note 3: Take care not to damage the lip portion of seal.
Note 4: Make sure that a spring does not drop off after
pressing in the seal.
Repair of valve seat
Remove carbon on the valve seat surface, then cut the
seat surface to eliminate nick and void with a seat cutter
(60°, 90°, 150°) so that the contact width becomes stan-
dard value (1.75).
vr
W05-02-23