Yamaha MTN850-A 2017, Service Manual, Page: 255 / 560

CYLINDER HEAD
5-20
EAS30276
REMOVING THE CYLINDER HEAD
1. Remove:
•
Intake camshaft
• Exhaust camshaft
Refer to “REMOVING THE CAMSHAFTS”
on page 5-11.
2. Remove:
• Cylinder head bolt (M6) (

4)
•
Cylinder head bolt (M9) (

8)
TIP
• Loosen the bolts in the proper sequence as
shown.
• Loosen each bolt 1/2 of a turn at a time. After
all of the bolts are fully loosened, remove them.
EAS30278
CHECKING THE TIMING CHAIN GUIDE
(EXHAUST SIDE)
1. Check:
• Timing chain guide (exhaust side)
Damage/wear

Replace.
EAS30277
CHECKING THE CYLINDER HEAD
1. Eliminate:
•
Combustion chamber carbon deposits
(with a rounded scraper)
TIP
Do not use a sharp instrument to avoid damag-
ing or scratching:
•
Spark plug bore threads
• Valve seats
2. Check:
•
Cylinder head
Damage/scratches

Replace.
•
Cylinder head water jacket
Mineral deposits/rust

Eliminate.
3. Measure:
• Cylinder head warpage
Out of specification

Resurface the cylinder
head.
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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.
TIP
To ensure an even surface, rotate the cylinder
head several times.
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8
1
2
3
4
5
6
7
8
9
10
11
12
4
Warpage limit
0.10 mm (0.0039 in)
Thickness gauge
90890-03180
Feeler gauge set
YU-26900-9