Subaru XT 1988 Service Manual page 213

ENGINE
2-3
VALVE AND VALVE SPRING
1) The valve has a small valve stem diameter [7 mm (0.28 in)
d ia.] to reduce the valve weight.
2) Both the intake and exhaust valve springs are non-linear-
pitch, double types.
3} The variable pitch valve spring is adopted to improve valve
follow-up performance at high engine speeds.
BELT TENSION ADJUSTER, TENSIONER
1) The belt tension adjuster is oil-filled and consists of a
spring and a special screw.
2) The adjuster used with the left timing belt automatically
adjusts and maintains belt tension.
3) The left belt tensioner is supported by a self-lubricating,
resin bearing.
Operation
The belt tension adjuster appl ies a constant load to the contact
portions and the arm and operates as follows:
• Operation in the direction of belt elongation
(1) If the left timing belt becomes loose, the adjuster
shaft turns counterclockwise by spring tension when
viewed from the bottom.
Spring
J:0')::;t;~f--
Shaft
Plug screw
L2-1287
(2) The rod wh ich meshes with the end of the adjuster
Fig. 118
shaft is then tifted.
The rod is not turned by the bearing but moves only up
and down.
(3) The cap, which is coupled to the rod with a cotter
pin, moves to push the tensioner arm up.
(4) When the force lowering the arm by belt tension and
the force to raising the cap by spring tension are balanced,
the shaft stops. This maintains constant belt tension.
• Operation in the direction of belt contraction
(Absorbs a change in belt length with a change in tempera-
ture)
Basically, the belt-tension adjuster operates in the reverse
manner of belt elongation.
A screw is used to connect the shaft and rod so that the ten-
sioner arm can be pushed up easily and not pushed down.
CAMSHAFT SPROCKET AND TIMING BELT
1) The camshaft sprocket has special round teeth featuring
positive engagement with belt teeth and smooth, low-noise
operation.
2) The timing belt is composed of a core featuring great
strength and less elongation, and a canvas (tooth face portion)
having superior wear resistance and highly heat-resistant
rubber.
3) A heavy load is applied to the left timing belt by the oil
pump. For this reason, this belt is 6 mm (0.24 in) wider than
the right belt.
TIMING BELT COVER
1) The resin-mold timing belt cover, consisting of five pieces,
is used to protect the timing belt against dust and water.
2) Right-hand side cover has an access hole for belt tensioner
adjustment.
57