4-Valve Cylinder Heads - Yanmar 3TNV82A-B Service Manual

ENGINE

4-Valve Cylinder Heads

The 4-valve cylinder head operates two valves with
a single rocker arm by employing a valve bridge
(Figure 6-80, (1)) between the two valves
(Figure 6-80, (2)). Clearance (Figure 6-80, (4))
between the valve bridge and valves must be set
before adjusting the clearance (Figure 6-80, (5))
between the rocker arm (Figure 6-80, (3)) and
valve bridge.
(5)
(1)
(4)
(2)
Figure 6-80
1. Remove the valve cover. See Removal of Valve
Cover on page 6-52.
Note: If adjusting each cylinder individually, the
cylinder to be adjusted first does not
have to be the No. 1 cylinder. Select and
adjust the cylinder where the piston is
nearest to the top dead center after
turning, and make adjustment for other
cylinders in the order of firing by turning
the crankshaft 180° each time.
2. Rotate the crankshaft clockwise as seen from
the coolant pump end, to bring No. 1 piston to
TDC on the compression stroke while watching
the rocker arm motion and the timing grid on the
flywheel. (Position where both the intake and
exhaust valves are closed.)
3. Make sure there is clearance (Figure 6-80, (5))
between the valve bridge (Figure 6-80, (1)) and
the rocker arm (Figure 6-80, (3)).
6-68
(3)
(2)
0001918B
Measuring and Adjusting Valve Clearance
IMPORTANT
Do not loosen or tighten the valve adjusting
screw lock nut without holding the valve
bridge. Always hold the valve bridge using a
wrench to prevent bending of the valve
stems.
4. Loosen the valve bridge adjusting screw lock
nut (Figure 6-81, (1)) while holding the bridge
(Figure 6-81, (3)) with a wrench
(Figure 6-81, (2)).
(3)
Figure 6-81
5. To assure the valve bridge contacts the rear
valve, apply light, downward (Figure 6-82, (4))
finger pressure on the valve bridge
(Figure 6-82, (3), and loosen the valve bridge
adjusting screw (Figure 6-82, (1)), until there is
visible clearance (Figure 6-84, (2)) between the
adjusting screw and the front valve.
6. To assure the valve bridge has equal contact
with the front and rear valves, apply light
downward (Figure 6-82, (4)) pressure on the
valve bridge (Figure 6-82, (3), adjust the valve
bridge adjusting screw ((Figure 6-82, (1)),
(Figure 6-84, (1))) so there is zero
"0" clearance (Figure 6-84, (2)) between the
adjusting screw and the front valve.
(4)
(3)
Figure 6-82
TNV DI Service Manual
(1)
(2)
0001917A
(1)
(2)
0001917C