Checking The Cylinder Head; Checking The Tappet Covers And Camshaft Sprocket Cover; Checking The Camshaft Sprocket And Timing Chain Guide (Exhaust System Side) - Yamaha XT250X Service Manual

4
5
EAS24160

CHECKING THE CYLINDER HEAD

1. Eliminate:
Combustion chamber carbon deposits
G
(with a rounded scraper)
NOTE:
Do not use a sharp instrument to avoid damag-
ing or scratching:
Spark plug bore threads
G
Valve seats
G
2. Check:
Cylinder head
G
Damage/scratches → Replace.
3. Measure:
Cylinder head warpage
G
Out of specification → Resurface the cylinder
head.
Warpage limit
0.03 mm (0.0012 in)
MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
a. Place a straightedge "1" and a thickness
gauge "2" across the cylinder head.
b. Measure the warpage.
c. If the limit is exceeded, resurface the cylinder
head as follows.
d. Place a 400–600 grit wet sandpaper on the
surface plate and resurface the cylinder head
using a figure-eight sanding pattern.
NOTE:
To ensure an even surface, turn the cylinder
6
2
1
3
head several times.
e. When the cylinder head warpage is out of
specification after resurfacing, replace the
cylinder head.
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EAS23940
CHECKING THE TAPPET COVERS AND
CAMSHAFT SPROCKET COVER
The following procedure applies to both of the
tappet covers and O-rings.
1. Check:
Tappet cover
G
Camshaft sprocket cover
G
EAS3C51005
CHECKING THE CAMSHAFT SPROCKET
AND TIMING CHAIN GUIDE (EXHAUST
SYSTEM SIDE)
Check the camshaft sprocket and the timing
chain guide (exhaust system side) as follows.
1. Check:
Camshaft sprocket
G
Wear of 1/4 or more teeth "a" → Replace the
camshaft sprocket as a set, timing chain, and
crankshaft sprocket.
a
b
a. 1/4 tooth wear
b. Normal
1. Timing chain
2. Camshaft sprocket
5-9
CYLINDER HEAD
1
2
1
2