TOHATSU BFT75A Service Manual page 393

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CYLINDER HEAD
VALVE SEAT WIDTH
Thoroughly clean the combustion chambers and valve
seats to remove carbon deposits. Apply a light coat of
Prussian Blue compound or erasable felt-tipped marker
ink to the valve faces.
Insert the valves, and then lift them and snap them
closed against their seats several times. Be sure the
valve does not rotate on the seat. The transferred
marking compound will show any area of the seat that
is not concentric.
Measure the valve seat width.
STANDARD:
IN: 0.85 – 1.15 mm (0.033 – 0.045 in)
EX: 1.25 – 1.55 mm (0.049 – 0.061 in)
SERVICE LIMIT:
IN: 1.60 mm (0.063 in)
EX: 2.00 mm (0.079 in)
If the valve seat width is too wide or narrow, or if the
valve seat is too high or low, recondition the valve seat
(page 14-41).
VALVE SEAT INSTALLATION HEIGHT
Measure the valve seat installation height [1].
STANDARD:
IN: 46.0 – 46.6 mm (1.81 – 1.83 in)
EX: 46.1 – 46.7 mm (1.81 – 1.84 in)
SERVICE LIMIT:
IN: 46.9 mm (1.85 in)
EX: 47.0 mm (1.85 in)
If the measurement exceeds the service limit, replace
the cylinder head with a new one (page 14-22).
ROCKER ARM SHAFT O.D.
Measure and record the rocker arm shaft O.D. at the
sliding part of each rocker arm.
STANDARD:
19.972 – 19.993 mm (0.7863 – 0.7871 in)
Replace the rocker arm shaft if its O.D. is smaller than
the standard (page 14-30).
14-34
VALVE SEAT
TOO LOW
VALVE SEAT
TOO HIGH
[1]