Checking The Timing Chain And Camshaft Sprocket; Checking The Timing Chain Tensioners; Checking The Decompression System - Yamaha YZ 2020 Series Owner's Service Manual

5. Measure:
• Camshaft journal diameter "a"
Out of specification  Replace the camshaft.
Within specification  Replace the cylinder
head and the camshaft caps as a set.
Camshaft journal diameter
21.959–21.972 mm (0.8645–
0.8650 in)
EAM30082
CHECKING THE TIMING CHAIN AND
CAMSHAFT SPROCKET
1. Check:
• Timing chain "1"
Damage/stiffness  Replace the timing
chain and camshaft as a set.
2. Check:
• Camshaft sprocket
More than 1/4 tooth wear "a"  Replace the
camshaft and the timing chain as a set.
a
b
1 1 1
a. 1/4 tooth
b. Correct
1. Timing chain roller
2. Camshaft sprocket
EAM30083
CHECKING THE TIMING CHAIN
TENSIONERS
1. Check:
• Timing chain tensioner
Crack/damage  Replace.
a. While pressing the tensioner rod lightly
with your fingers, use a thin screwdriver
"1" to wind the tensioner rod up fully clock-
wise.
b. When releasing the screwdriver by press-
ing lightly with your fingers, make sure that
the tensioner rod will come out smoothly.
c. If not, replace the tensioner assembly.
EAM30084

CHECKING THE DECOMPRESSION SYSTEM

1. Check:
• Decompression system
5-18
CAMSHAFT
1
2