Yanmar 4TNE98, Service Manual

Page: 108 / 246

4TNV98 & 4TNE98 Diesel Engine Section 3. Engine 106
4TNV98 Engine
The 4-valve cylinder head operates two valves with
a single rocker arm by employing a valve bridge
(Figure 6-77, (1)) between the two valves (Figure 6-
77, (2)) . Clearance (Figure 6-77, (4)) between the
valve bridge and valves must be set before adjusting
the clearance
(Figure 6-77, (5)) between the rocker
arm (Figure 6-77, (3)) and valve bridge.
Figure 6-77
1. Remove the valve cover. See Removal of Valve
Cover on page 103.
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 6-77, (5))
between the valve bridge (Figure 6-77, (1)) and
the rocker arm (Figure 6-77, (3)) .
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 6-78, (1)) while holding the bridge (Figure
6-78, (3)) with a wrench (Figure 6-78, (2)) .
Figure 6-78
5. To assure the valve bridge contacts the rear valve,
apply light, downward (Figure 6-79, (4)) finger
pressure on the valve bridge (Figure 6-79, (3) ,
and loosen the valve bridge adjusting screw
(Figure 6-79, (1)) , until there is visible clearance
(Figure 6-81, (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
(Figure6-79,(4)) pressure on the valve bridge
(Figure6-79,(3)) , adjust the valve bridge adjusting
screw (Figure 6-79,(1)), (Figure 6-81,(1)) so
there is zero “0”clearance (Figure 6-81,(2))
between the adjusting screw and the front valve.
Figure 6-79