Yamaha MTN850-A 2017 User manual

2017
SERVICE MANUAL
MTN850-A
MTN850-AH
BS2-28197-E0

EAS20002
MTN850-A
MTN850-AH
SERVICE MANUAL
©2016 by Yamaha Motor Co., Ltd.
First edition, November 2016
All rights reserved.
Any reproduction or unauthorized use
without the written permission of
Yamaha Motor Co., Ltd.
is expressly prohibited.

EAS20003
IMPORTANT
This manual was produced by the Yamaha Motor Company, Ltd. primarily for use by Yamaha dealers
and their qualified mechanics. It is not possible to include all the knowledge of a mechanic in one man-
ual. Therefore, anyone who uses this book to perform maintenance and repairs on Yamaha vehicles
should have a basic understanding of mechanics and the techniques to repair these types of vehicles.
Repair and maintenance work attempted by anyone without this knowledge is likely to render the vehi-
cle unsafe and unfit for use.
Yamaha Motor Company, Ltd. is continually striving to improve all of its models. Modifications and sig-
nificant changes in specifications or procedures will be forwarded to all authorized Yamaha dealers and
will appear in future editions of this manual where applicable.
TIP
Designs and specifications are subject to change without notice.
EAS30001
IMPORTANT MANUAL INFORMATION
Particularly important information is distinguished in this manual by the following notations.
This is the safety alert symbol. It is used to alert you to potential per-
sonal injury hazards. Obey all safety messages that follow this symbol
to avoid possible injury or death.
A WARNING indicates a hazardous situation which, if not avoided, could
result in death or serious injury.
A NOTICE indicates special precautions that must be taken to avoid
damage to the vehicle or other property.
A TIP provides key information to make procedures easier or clearer.
WARNING
NOTICE
TIP

EAS20004
HOW TO USE THIS MANUAL
This manual is intended as a handy, easy-to-read reference book for the mechanic. Comprehensive
explanations of all installation, removal, disassembly, assembly, repair and check procedures are laid
out with the individual steps in sequential order.
•The manual is divided into chapters and each chapter is divided into sections. The current section title
“1” is shown at the top of each page.
•Sub-section titles “2” appear in smaller print than the section title.
•To help identify parts and clarify procedure steps, there are exploded diagrams “3” at the start of each
removal and disassembly section.
•Numbers “4” are given in the order of the jobs in the exploded diagram. A number indicates a disas-
sembly step.
•Symbols “5” indicate parts to be lubricated or replaced.
Refer to “SYMBOLS”.
•A job instruction chart “6” accompanies the exploded diagram, providing the order of jobs, names of
parts, notes in jobs, etc. This step explains removal and disassembly procedure only. For installation
and assembly procedure, reverse the steps.
•Jobs “7” requiring more information (such as special tools and technical data) are described sequen-
tially.
CLUTCH
5-38
EAS20055
CLUTCH
Removing the clutch cover
Order Job/Parts to remove Q’ty Remarks
Engine oil
Drain.
Refer to “CHANGING THE ENGINE OIL” on
page 3-24.
.tcennocsiD1elbachctulC1
1revoC2
3O2sensor coupler bracket 1
1revochctulC4
1teksagrevochctulC5
2niplewoD6
1pacrellifliO7
1
2
3
4
5
6
7
6
(6)
12 N
・
m (1.2 kgf
・
m, 8.7 lb
・
ft)
12 N
・
m (1.2 kgf
・
m, 8.7 lb
・
ft)
12 N
・
m (1.2 kgf
・
m, 8.7 lb
・
ft)
1.5 N
・
m (0.15 kgf
・
m, 1.1 lb
・
ft)
7 N
・
m (0.7 kgf
・
m, 5.1 lb
・
ft)
CLUTCH
5-43
8. Remove:
•Clutch boss nut
•Conical spring washer
•Washer
•Clutch boss
•Thrust plate
•Clutch housing
•Oil pump drive chain
EAS30348
CHECKING THE FRICTION PLATES
The following procedure applies to all of the fric-
tion plates.
1. Check:
•Friction plate 1, 2
Damage/wear →Replace the friction plates
as a set.
2. Measure:
•Friction plate 1, 2 thickness
Out of specification →Replace the friction
plates as a set.
TIP
Measure the friction plate at four places.
EAS30349
CHECKING THE CLUTCH PLATES
The following procedure applies to all of the
clutch plates.
1. Check:
•Clutch plate 1, 2
Damage →Replace the clutch plates as a
set.
2. Measure:
•Clutch plate 1, 2 thickness
(with a surface plate and thickness gauge “1”)
Out of specification →Replace the clutch
plates as a set.
3. Measure:
•Assembly width “a” of the friction plates and
clutch plates
Friction plate 1 thickness
2.92–3.08 mm (0.115–0.121 in)
Wear limit
2.82 mm (0.111 in)
Friction plate 2 thickness
2.92–3.08 mm (0.115–0.121 in)
Wear limit
2.82 mm (0.111 in)
2
1
3
A. Friction plate 1
B. Friction plate 2
Thickness gauge
90890-03180
Feeler gauge set
YU-26900-9
Clutch plate 1 thickness
2.20–2.40 mm (0.087–0.094 in)
Warpage limit
0.10 mm (0.004 in)
Clutch plate 2 thickness
1.90–2.10 mm (0.075–0.083 in)
Warpage limit
0.10 mm (0.004 in)

EAS20005
SYMBOLS
The following symbols are used in this manual for easier understanding.
TIP
The following symbols are not relevant to every vehicle.
SYMBOL DEFINITION SYMBOL DEFINITION
Serviceable with engine mounted Gear oil
Filling fluid Molybdenum disulfide oil
Lubricant Brake fluid
Special tool Wheel bearing grease
Tightening torque Lithium-soap-based grease
Wear limit, clearance Molybdenum disulfide grease
Engine speed Silicone grease
Electrical data Apply locking agent (LOCTITE®).
Engine oil Replace the part with a new one.
Silicone fluid
G
M
BF
B
T
R
.
.
LS
M
S
LT
E
New
S

GENERAL INFORMATION 1
SPECIFICATIONS 2
PERIODIC CHECKS AND ADJUSTMENTS 3
CHASSIS 4
ENGINE 5
COOLING SYSTEM 6
FUEL SYSTEM 7
ELECTRICAL SYSTEM 8
TROUBLESHOOTING 9
EAS10003
TABLE OF CONTENTS

1
2
3
4
5
6
7
8
9
GENERAL INFORMATION
IDENTIFICATION..............................................................................................1-1
VEHICLE IDENTIFICATION NUMBER ......................................................1-1
MODEL LABEL...........................................................................................1-1
FEATURES .......................................................................................................1-2
YCC-T (Yamaha Chip Controlled Throttle).................................................1-2
OUTLINE OF THE TCS (Traction Control System)....................................1-4
INSTRUMENT FUNCTIONS ......................................................................1-8
IMPORTANT INFORMATION .........................................................................1-13
PREPARATION FOR REMOVAL AND DISASSEMBLY..........................1-13
REPLACEMENT PARTS..........................................................................1-13
GASKETS, OIL SEALS AND O-RINGS ...................................................1-13
LOCK WASHERS/PLATES AND COTTER PINS ....................................1-13
BEARINGS AND OIL SEALS ...................................................................1-13
CIRCLIPS .................................................................................................1-14
RUBBER PARTS......................................................................................1-14
BASIC SERVICE INFORMATION ..................................................................1-15
QUICK FASTENERS................................................................................1-15
ELECTRICAL SYSTEM............................................................................1-16
SPECIAL TOOLS ...........................................................................................1-20

IDENTIFICATION
1-1
EAS20007
IDENTIFICATION
EAS30002
VEHICLE IDENTIFICATION NUMBER
The vehicle identification number “1” is stamped
into the right side of the steering head pipe.
EAS30003
MODEL LABEL
The model label “1” is affixed to the frame. This
information will be needed to order spare parts.
1
1

FEATURES
1-2
EAS20008
FEATURES
EAS30852
YCC-T (Yamaha Chip Controlled Throttle)
Mechanism characteristics
Yamaha developed the YCC-T system employing the most advanced electronic control technologies.
Electronic control throttle systems have been used on automobiles, but Yamaha has developed a fast-
er, more compact system specifically for the needs of a sports motorcycle. The Yamaha-developed
system has a high-speed calculating capacity that produces computations of running conditions every
1/1000th of a second.
The YCC-T system is designed to respond to the throttle action of the rider by having the ECU instan-
taneously calculate the ideal throttle valve opening and generate signals to operate the motor-driven
throttle valves and thus actively control the intake air volume.
The ECU contains two CPUs with a capacity about five times that of conventional units, making it pos-
sible for the system to respond extremely quickly to the slightest adjustments made by the rider. In par-
ticular, optimized control of the throttle valve opening provides the optimum volume of intake air for
easy-to-use torque, even in a high-revving engine.
Aims and advantages of using YCC-T
•Increased engine power
By shortening the air intake path, higher engine speed is possible Increased engine power.
•Improved driveability
Air intake volume is controlled according to the operating conditions Improved throttle response to
meet engine requirement.
Driving force is controlled at the optimal level according to the transmission gear position and engine
speed Improved throttle control.
•Engine braking control
Due to the throttle control, optimal engine braking is made possible.
•Simplified idle speed control (ISC) mechanism
The bypass mechanism and ISC actuator are eliminated A simple mechanism is used to maintain
a steady idle speed.
•Reduced weight
Compared to using a sub-throttle mechanism, weight is reduced.
12
3
4
1. Accelerator position sensor
2. Throttle servo motor
3. Throttle position sensor
4. Throttle valves

FEATURES
1-3
YCC-T system outline
5
6
7
8
9
32
1
4
1. Throttle position sensor
2. Throttle servo motor
3. Accelerator position sensor
4. ECU (Engine Control Unit)
5. Sensor input
6. Gear position switch
7. Crankshaft position sensor
8. Rear wheel sensor
9. Coolant temperature sensor

FEATURES
1-4
EAS30855
OUTLINE OF THE TCS (Traction Control System)
The traction control system controls excessive spinning (slipping) of the rear wheel when accelerating
on slippery surfaces, such as unpaved or wet roads.
The ECU monitors the front and rear wheel speeds using the signals from the front and rear wheel sen-
sors, and detects rear wheel slipping according to the difference between the wheel speeds. If the slip-
ping exceeds the preset value, the ECU controls the slipping using integrated control of the ignition
timing, fuel cut-off, and throttle valve opening of the YCC-T system.
The traction control system can be set to one of two operation modes or turned off.
TCS (Traction control system) layout
12 3
6
7
8, 9
10
45
1. Traction control system indicator light
2. Traction control system switch
3. ECU
4. Throttle servo motor
5. ABS ECU
6. Rear wheel sensor
7. Front wheel sensor
8. Ignition coils
9. Spark plugs
10.Fuel injector

FEATURES
1-5
TCS (Traction control system) block diagram
The signals from the front and rear wheel sensors are sent to the ECU through the ABS ECU, and the
ECU calculates the amount of slip according to the difference between the detected front and rear
wheel speeds.
If the amount of slip exceeds the preset value, the ECU controls the ignition timing, fuel cut-off, and
throttle valve opening of the YCC-T system so that the amount of slip is less than the preset value. The
traction control system indicator light in the meter assembly flashes when the traction control system
has activated.
1A
B
D
G
E
H
F
5
C
A
4
3
2
1. Front wheel sensor
2. Rear wheel sensor
3. ABS ECU
4. Traction control system switch
5. ECU
A. Signal conversion
B. Slip amount calculation
C. Exceeds preset value
D. Actuator control
E. Fuel cut-off
F. Ignition timing (retarded)
G. Traction control system indicator light
(flashes)
H. YCC-T motor throttle valve opening
(decreased)

FEATURES
1-6
Traction control system
The traction control system (TCS) helps maintain traction when accelerating on slippery surfaces,
such as unpaved or wet roads. If sensors detect that the rear wheel is starting to slip (uncontrolled
spinning), the traction control system assists by regulating engine power as needed until traction is
restored.
WARNING
EWA15433
The traction control system is not a substitute for riding appropriately for the conditions. Trac-
tion control cannot prevent loss of traction due to excessive speed when entering turns, when
accelerating hard at a sharp lean angle, or while braking, and cannot prevent front wheel slip-
ping. As with any vehicle, approach surfaces that may be slippery with caution and avoid espe-
cially slippery surfaces.
Setting the traction control system
With the throttle closed, push this switch down to change from TCS “1” to TCS “2”. Push up to change
from “2” to “1”.
With the vehicle stopped, push this switch up for two seconds to turn the system off. Push down to turn
the system on.
The “ ” indicator light flashes when traction control has engaged. You may notice slight changes in
engine and exhaust sounds when the system has engaged.
When the traction control system has been set to “OFF”, the “ ” indicator light will come on.
TCS “OFF”
TCS “OFF” turns the traction control system off.
TCS “1”
TCS “1” minimizes traction control system assist.
TCS “2”
TCS “2” maximizes traction control assist; wheel spin is most strongly controlled.
NOTICE
ECA19650
Use only the specified tires. Using different sized tires will prevent the traction control system
from controlling tire rotation accurately.
TIP
•The current TCS setting is shown in the TCS display.
•Traction control can be turned on or off only when the vehicle is stopped.
•When the key is turned to “ON”, traction control is turned on and set to TCS “1” or “2” (whichever was
last selected).
•Turn the traction control system off to help free the rear wheel if the vehicle gets stuck in mud, sand,
or other soft surfaces.
12
1. Traction control system switch “ ”
2. TCS display

FEATURES
1-7
Resetting the traction control system
The traction control system will automatically disable when:
•the front wheel or rear wheel comes off the ground while riding.
•excessive rear wheel spin is detected while riding.
•either wheel is rotated with the key turned to “ON” (such as when performing maintenance).
If the traction control system is disabled, both the “ ” indicator light and the “ ” warning light will come
on.
Should this occur, try resetting the system as follows.
1. Stop the vehicle and turn the key to “OFF”.
2. Wait a few seconds and then turn key back to “ON”.
3. The “ ” indicator light should turn off and the system be enabled.
4. Check the vehicle and turn off the “ ” warning light.
TIP
If the “ ” indicator light or the “ ” warning light remains on after resetting, check the fuel injection sys-
tem (Refer to “FUEL INJECTION SYSTEM” on page 8-33).
Quick shift system
The quick shift system (QS) allows for full-throttle, clutch lever-less, electronically-assisted upshifts.
When the shift switch detects motion in the shift pedal, engine power and drive torque are momentarily
adjusted to allow the upshift to occur.
TIP
•The quick shift system operates when traveling at least 20 km/h (12 mi/h) with an engine speed of
2300 r/min or higher, and only when accelerating.
•It does not operate when the clutch lever is pulled.

FEATURES
1-8
EAS30682
INSTRUMENT FUNCTIONS
Multi-function meter unit
WARNING
EWA12423
Be sure to stop the vehicle before making
any setting changes to the multi-function
meter unit. Changing settings while riding
can distract the operator and increase the
risk of an accident.
The multi-function meter unit is equipped with
the following:
•a speedometer
•a tachometer
•a clock
•a fuel meter
•an eco indicator
•a transmission gear display
•a drive mode display
•a TCS display
•a multi-function display
TIP
•Except when switching to the brightness con-
trol mode or to display the clock, turn the key to
“ON” before using the “SELECT” and “RESET”
buttons to adjust the multi-function meter.
•To switch the speedometer and multi-function
displays between kilometers and miles, press
the “SELECT” button for one second.
Speedometer
The speedometer shows the vehicle’s traveling
speed.
Tachometer
The tachometer allows the rider to monitor the
engine speed and keep it within the ideal power
range.
NOTICE
ECA19660
Do not operate the engine in the tachometer
red zone.
1. “SELECT” button
2. “RESET” button
1. Transmission gear display
2. Tachometer
3. Eco indicator “ECO”
4. TCS display
5. Drive mode display
6. Fuel meter
7. Multi-function display
8. Clock
9. Speedometer
21
1 2 43 5 6
789
1. Speedometer
1. Tachometer
2. Tachometer red zone
1
21

FEATURES
1-9
Clock
The clock uses a 12-hour time system. When
the key is not in the “ON” position, the clock can
be viewed by pushing the “SELECT” button.
To set the clock
1. Turn the key to “ON”.
2. Push the “SELECT” button and the “RESET”
button for two seconds.
3. When the hour digits start flashing, use the
“RESET” button to set the hours.
4. Push the “SELECT” button, and the minute
digits will start flashing.
5. Use the “RESET” button to set the minutes.
6. Push the “SELECT” button to confirm the set-
tings and start the clock.
Fuel meter
The fuel meter indicates the amount of fuel in the
fuel tank. The display segments of the fuel meter
disappear from “F” (full) towards “E” (empty) as
the fuel level decreases. When the last segment
starts flashing, refuel as soon as possible.
TIP
If a problem is detected in the electrical circuit,
the fuel level segments and “ ” will flash repeat-
edly. Check the electrical circuit. Refer to
“CHECKING THE FUEL METER/FUEL LEVEL
WARNING LIGHT” on page 8-168.
Eco indicator
This indicator comes on when the vehicle is be-
ing operated in an environmentally friendly, fuel-
efficient manner. The indicator goes off when
the vehicle is stopped.
TIP
Consider the following tips to reduce fuel con-
sumption:
•Avoid high engine speeds during acceleration.
•Travel at a constant speed.
•Select the transmission gear that is appropri-
ate for the vehicle speed.
Transmission gear display
This display shows the selected gear. The neu-
tral position is indicated by “ ” and by the neutral
indicator light.
1. Clock
1. Fuel meter
1
1
1. Eco indicator “ECO”
1. Transmission gear display
2. Neutral indicator light “ ”
1
1 2

FEATURES
1-10
Drive mode display
This display indicates which drive mode has
been selected: “STD”, “A” or “B”. For more de-
tails on the modes and on how to select them,
refer to “D-mode (drive mode)” on page 1-12.
TCS display
This display indicates which traction control sys-
tem setting has been selected: “1”, “2” or “OFF”.
For more details on the TCS settings and on
how to select them, refer to “OUTLINE OF THE
TCS (Traction Control System)”.
Multi-function display
The multi-function display is equipped with the
following:
•an odometer
•two tripmeters
•a fuel reserve tripmeter
•an instantaneous fuel consumption display
•an average fuel consumption display
•a coolant temperature display
•an air intake temperature display
•a brightness control display
TIP
•The odometer will lock at 999999 and cannot
be reset.
•The tripmeters will lock at 9999.9 but can be
manually reset.
Push the “SELECT” button to switch the display
between the instantaneous fuel consumption
mode “km/L” or “L/100 km”, average fuel con-
sumption mode “AVE_ _._ km/L” or “AVE_ _._
L/100 km”, coolant temperature mode “C”, air
intake temperature mode “Air_ _ C”, odometer
mode “ODO”, and tripmeter modes “TRIP 1” and
“TRIP 2” in the following order:
km/L or L/100 km AVE_ _._ km/L or AVE_ _._
L/100 km C Air_ _ C ODO TRIP 1
TRIP 2
When the display units have been set to miles:
km/L, L/100 km or MPG AVE_ _._ km/L,
AVE_ _._ L/100 km or AVE_ _._ MPG C 
Air_ _ C ODO TRIP 1 TRIP 2
TIP
Push the “RESET” button to switch the display in
the reverse order.
If the last segment of the fuel meter starts flash-
ing, the display automatically changes to the fuel
reserve tripmeter mode “F-TRIP” and starts
counting the distance traveled from that point. In
this case, push the “SELECT” button to switch
the display in the following order:
F-TRIP km/L or L/100 km AVE_ _._ km/L
or AVE_ _._ L/100 km C Air_ _ C ODO
TRIP 1 TRIP 2 F-TRIP
When the display units have been set to miles:
F-TRIP km/L, L/100 km or MPG AVE_ _._
km/L, AVE_ _._ L/100 km or AVE_ _._ MPG 
C Air_ _ C ODO TRIP 1 TRIP 2 
F-TRIP
TIP
•To reset a tripmeter, select it by pushing the
“SELECT” button, and then push the “RESET”
button for one second.
1. Drive mode display
1. TCS display
1. Multi-function display
1
1
1

FEATURES
1-11
•If you do not reset the fuel reserve tripmeter
manually, it resets automatically and disap-
pears after refueling and traveling 5 km (3 mi).
Instantaneous fuel consumption mode
The instantaneous fuel consumption display can
be set to either “km/L”, “L/100 km” or “MPG”
(when the display units have been set to miles).
•“km/L”: The distance that can be traveled on
1.0 L of fuel under the current riding conditions
is shown.
•“L/100 km”: The amount of fuel necessary to
travel 100 km under the current riding condi-
tions is shown.
•“MPG”: The distance that can be traveled on
1.0 Imp.gal of fuel under the current riding con-
ditions is shown.
To switch between the instantaneous fuel con-
sumption display settings, push the “SELECT”
button for one second.
TIP
If traveling at speeds under 20 km/h (12 mi/h),
“_ _._” is displayed.
Average fuel consumption mode
This display shows the average fuel consump-
tion since it was last reset.
The average fuel consumption display can be
set to either “AVE_ _._ km/L”, “AVE_ _._ L/100
km” or “AVE_ _._ MPG” (when the display units
have been set to miles:).
•“AVE_ _._ km/L”: The average distance that
can be traveled on 1.0 L of fuel is shown.
•“AVE_ _._ L/100 km”: The average amount of
fuel necessary to travel 100 km is shown.
•“AVE_ _._ MPG”: The average distance that
can be traveled on 1.0 Imp.gal of fuel is shown.
To switch between the average fuel consump-
tion display settings, push the “SELECT” button
for one second.
To reset the average fuel consumption, push the
“RESET” button for one second.
TIP
After resetting the average fuel consumption,
“_ _._” will be shown until the vehicle has trav-
eled 1 km (0.6 mi).
Coolant temperature mode
This display shows the coolant temperature from
40 C to 116 C in 1 C increments.
If the message “HI” flashes, stop the vehicle,
then stop the engine, and let the engine cool.
TIP
•When the coolant temperature is below 40 C,
“Lo” will be displayed.
•The coolant temperature varies with changes
in the weather and engine load.
Air intake temperature mode
The air intake temperature display indicates the
1. Instantaneous fuel consumption display
1. Average fuel consumption display
1
1
1. Coolant temperature display
1. Air intake temperature display
1
1