TOHATSU BFT115A Service Manual page 438

CYLINDER HEAD
VALVE STEM-TO-VALVE GUIDE
CLEARANCE
Subtract each valve stem O.D. from the corresponding
valve guide I.D.
STANDARD:
IN: 0.030 – 0.055 mm (0.0012 – 0.0022 in)
EX: 0.055 – 0.080 mm (0.0022 – 0.0031 in)
SERVICE LIMIT:
IN: 0.080 mm (0.0031 in)
EX: 0.110 mm (0.0043 in)
If the stem-to-guide clearance exceeds the service limit,
determine if the new guide with standard dimensions
would bring the clearance within tolerance. If so,
replace any guide as necessary and ream to fit (page
14-52). If the stem-to-guide clearance exceeds the
service limit with new guides, replace the valves as well.
• Recondition the valve seats whenever the valve
guides are replaced (page 14-54).
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 (1).
STANDARD:
IN/EX: 1.25 – 1.55 mm (0.049 – 0.061 in)
SERVICE LIMIT:
IN/EX: 2.0 mm (0.08 in)
If the valve seat width is under the standard, or over the
service limit, or if the valve seat is too high/low,
recondition the valve seat (page 14-54).
VALVE INSTALLATION HEIGHT
Measure the valve installation height (1).
STANDARD:
IN: 44.00 – 44.60 mm (1.732 – 1.756 in)
EX: 44.00 – 44.60 mm (1.732 – 1.756 in)
14-46
VALVE SEAT
TOO LOW
(1)
VALVE SEAT
TOO HIGH
(1)