2. Inspection and adjustment
23
(5) Adjusting the intake/exhaust valve clearance
Make measurement and adjustment while the engine is cold.
1) Valve clearance measurement
a) Remove the rocker arm cover above cylinder
head.
b) Set the No.1 cylinder in the compression TDC
Turn the crankshaft to bring the piston of the
No.1 cylinder to its compression top dead center
while watching the rocker arm motion, the timing
mark of the flywheel housing and the top mark of
the flywheel.
(Position where both the intake and exhaust
valves are closed.)
(Notes)
• The crankshaft shall be turned clockwise as seen
from the gear case side.
• The No.1 cylinder position is on the opposite side of the gear case.
• Since there is a clearance between the rocker arm and valve at the compression top dead center, the
position of TDC can be checked by hand. Also see that the top mark on the flywheel aligns with the
mark on the flywheel housing. If there is no valve clearance, disassemble and inspect around the
valve seat, since the valve seat may be worn abnormally.
c) Valve clearance measurement
Insert a thickness gage between the rocker arm
and valve cap, and record the measured valve
clearance.
(Use it as the data for estimating the wear state.)
d) Adjusting other cylinders
Turn the crankshaft 240
°
and make adjustment
for the No.3 cylinder. Then adjust the No.2
cylinder in this order.
The cylinder to be adjusted first does not have to
be the No.1 cylinder. Select and adjust the
cylinder where the piston is the nearest to the top
dead center after turning, and make adjustment for other cylinders in the order of ignition by
turning the crankshaft 240
° e
ach time.
The adjustment method of reducing the flywheel turning numbers (for reference):
Set No.1 cylinder to the compression T.D.C. and adjust the clearance of the
z
mark of the below
table. Next, turn the flywheel once (the suction/ exhaust valve of No.1 cylinder is in the position of
the overlap T.D.C. at this time), and adjust the clearance of the
{
mark.
Ignition order of 3 cylinder engines: 1
→
3
→
2
2) Valve clearance inspection and adjustment
a) Loosen adjusting bolts
Loosen the lock nut and adjust the screw. And
check the valve for any inclination of valve cap,
entrance of dirt or wear.
Cylinder No.
1
2
3
Valve
Suction
Exhaust
Suction
Exhaust
Suction
Exhaust
No.1 compression
T.D.C
z
z
z
z
The first time
No.1 overlap T.D.C
{
{
The second time
Hole
Flywheel
housing
Injection
timing marks
Flywheel
T.D.C.
No.1 cylinder
1
Valve
clearance
Rocker arm
(Valve clearance)
Adjusting screw
Lock nut
(Normal)
(Abnormal)
Valve cap
Summary of Contents for 3YM20
Page 1: ...M9961 03E100 ...
