Yamaha JT2M (1972), JT1 (1971), JT1L (1971), JT2 (1972) Service Manual

.........

;""'

~

-~-tr::c';:}';.;··

..

:''= · •

YAMAHA

JT1---JT2

SERIES

· . · ·

.

SERVICE

MANUAL·

-

NOTICE

This manual has been written by Yamaha Motor Company for use by Authorized Yamaha Dealers and their qualified mechanics. certain basic mechanical precepts and procedures inherent to our product are a'lready

In

light of this purpose it has been assumed that

known and understood Without such basic knowlege, repairs or service to this model may render the machine unsafe. and for this reason by

an

Authorized Yamaha dealer who knowledge. Other information is produced by the Corporation. and The Research. Engineering. and further improve all models manufactured by the company. Modifications are therefore evitable and changes Yamaha Dealers and will. where applicable. appear

by

the reader.

we

must advise that all repairs

is

in

possession of the requisite basic product

U.

is

necessary to provide total technical coverage regarding the product.

Service

in

specifications or procedures will be forwarded to all

YAMAHA

JT

1st

EDITION,

2nd

Departments of Yamaha are continually striving to

in

SERIES

EDITION,

SERVICE

DECEMBER 1973

MAY

and/or

S. distributor. Yamaha International

future editions of this manual.

service be performed

Authorized

MANUAL

1976

in-

i

f

©DECEMBER

1973

YAMAHA

BUENA

INTERNATIONAL

PARK,

CALIFORNIA

LIT-11612-88-99

CORPORATION

90620

. '

~·

.

'

FOREWORD

The new Yamaha Endure

suspension

Its

exRerienced

This service manual

techn1c1ans in this goal.

YAMAHA

combine

rugged design

riders

the repair

top

cond1t1on

vein.

We

MINI

ENDURO. though small

The

60

cc engine. four. speed gearbox. tubular frame

to

provide

and

excellent performance also make it

as

well.

has

1nstruct1ons

hope that

been

an

ideal

vehicle

prepared

you

1n

order to provide all Yamaha dealers

and

technical information required

will find this manual most helpful

for

in

the

size.

younger

is

a fully functional motorcycle

and

rider.

an

intriguing

d1vers1on

to

keep

and

for older. more

and

the

valuable

MINI-ENDURO

in

the

fully functional

their service

in

carrying out

YAMAHA MOTOR CO., l TD.

ENGINEERING & SERVICE DEPARTMENT

MOOEL

IDENTIFICATION

This manual was originally printed for include information for

Generally speaking, since

the

JT1 was released

a JT1 with lighting kit.

the

JT1,

JT1

there

were no major changes

for

the

1971 model year.

The

JT2

Land

had various internal engine changes reliability and carburetor changes upgraded wanted a Mini-motocrosser given in

MOOEL

JT1 JT1 L JT2 JT2M

in

intensity. The JT2M was styled after

the

table below.

YEAR

1971 1971(½) 1972 1972

without

IBM

ID

NUMBER

288

338

288 288

lights. Additional identification information

ENGINE

the

JT2

Mini-Enduro. It has been edited

JT2M models.

to

any

of

the

Mini-Enduro models

The

JT1 L (1971½ release) was

to

improve

to

improve performance.

the

JT1 for those people who

STARTING

NUMBER

JT2

lights were

IDENTIFYING

COLOR

JT1-000101 Desert Orange JT1-200101 Desert Orange JT1-050101 Mandarin Orange JT1-300101 Competition Yellow

to

is

CONTENTS

CHAPTER 1 GENERAL

1-

1 Profile ··············································································································--···--·--··

1-

2 Features ··--··--···----·--········--···--·--·················--·--·--·--·--·--················································ 2

1 - 3 Specifications and Performance ·----·--·············································--·--------·------·--··--·--· 3

1 - 4 Performance Curves ·······················--·· ··--··--······--···--····----·--·--····································· 5

1 - 5 Tools and Instruments for shop service ··································--··--·--···--··------·--·---------- 6

CHAPTER 2 YAM

2 - What 2-

2 Features of Yamaha Autolube --··----------··--···--···················--·----------------·--·--··--··----·--··· 7

2 - 3 Handling

CHAPTER 3 ENGINE

3 - Engine 3 - 2 Cylinder Head ···········································--··------------------------···----····----······················ 3-

3 Cylinder ·······················--···········································--·--·----·--·--··--······················--······

3-

4 Piston 3 - 5 Piston Ring ·········--·········--·--·--································--····----------------··--···························

3 - 6 Piston ----·--·--·······--·--·--·--·······--······--··· ·········································----·--·----·········· ..........

3 - 7 Flywheel Magneto ···································--·--·----··--------··----·--·--·--··········--········----·------· 3-

8 Crankcase Cover (RH)·····························--·--·--------------·--·--···························--··--·----

.................................................................................................................... .

AHA

AUTOLU

is

Yamaha Autolube? --------------------------···························---------------------------------- 7

the

BE

·--·----·--------·----·--·----······

Oil Pump --------------··------------------··----·························----··--------------------·-- 7

·················--·--··--·--·------····--··------·--·--······ 7

·························································-------------------- ----···································· 1 I

Remova1

----------------------------------···--······································----··------------·--------·· I 1

--··········--······--··················--···--············--·--·------------·------··--··························· 17

15 16

18 19

20

21

3-

9 Clutch ············································----·--·--·--··--·······--······················--····--···--··--····--·--··· 22

3-10

3 -

3-12 3-13

3 3 3

3 - 17 Crankshaft ·--··--··--·········--········································--··----·······························--·--·----····

3-18

Primary Drive Gear··················--····--·····················--·--------------·························--·--·----· 27

11

Kick Starter Mechanism ·····································----------··--·--···················--·----------··---- 27

Shift Mechanism ----·············--···································--------------························--·------··-Rotary Valve····--·····--········································--······------····························------········ 31

14

Drive Sprocket ················································--······----------·····························--··----····

15

Crankcase --·--························--·········----------------·----------··························--------------·--·····

-16

Transmission Assembly ----·····--·--······································--------------------··················----

Bearings

and

Oil

Seals

.............................................. --·······················----········----······· 41

-3-19 Carburetor ····--·····--·························--··········--·············--·--·················------·--·····--·--········

29

33 35 36

38

42

3 - 20

Air

Cleaner ................................................................................................................ 44

CHAPTER

4

CHASSIS

4-

1 Front

4-

2 Rear

4-

3 Rear Wheel Sprocket ............................................................................................... 53

.................................................................................................................... 46

Wheel

.............................................................................................................. 46

............................................................................................................... 49

4 - 4 Tires and Tubes ........................................................................................................ 54

4-

5 Front Forks ............................................................................................................... 54

4-

6 Rear Shocks ............................................................................................................. 57

4-

7 Gas Tank .................................................................................................................. 58

4 - 8 Rear Swing

Arm

...................................................................................................... 58

4 - 9 Steering Head ........................................................................................................... 60

4-

10

Oil

Tank and

4 -

11

Frame ........................................................................................................................

4 -

12

Handlebars ................................................................................................................

Tool

Box............................................................................................

'

4-13Miscellaneous ............................................................................................................

CHAPTER

5

ELECTRICAL

5-1 Electrical

5-

2

List

of

Electrical

5-

3 Ignition System-Function and Service .......................................................................... 63

5-

4 Ignition

5-

5 Ignition

5-

6 Condenser

5-

7

Charging

5·

8 Battery ............................................................................

5-

9 Checking the

5-

10

Spark

Plug

SYSTEM

............................................................................................... 62

Equipment..................................................................................................... 62

Components ..................................................................................... 62

Timing Coil

..

.........................................................................................................

..... ........................................................................................................... 64

..

. .

... . .. .. ..

..

. . .

... ... ... ... ...

......

...

....

... ... ... ... ... ...

.. . ...

..

... . ... . ..

..

. . . . .....

...

..

. .

..

System...........................................................................................................

•···· • •··

• •

•· • •···

• • •

•··

•···

•·

•·····

main

Switch .............................................................................................

.......................................................................................................................

....

· · ·

...

··

..

...

····· · ·

61 61 61 61

63

. .

64 65 67

69 69

APPENDICES

..................................................................................................................

I Parts

II

Ill IV

V

VI

and

Service

Bulletins..................................................................................

Parts Illustrations..............................................................................................

Maintenance Pre-operation Torque Cleaning Metric

Values

and

Inch

and

Lubrication

Check

for

Storage

Conversion

Intervals....................................................................

List....................................................................................

Common

Components...................................................................

Hints

.............................................. .................................

Tables..............................................................................

72 72 82 86 87 87

..

88 89

:E

0

d:

'•

m

i5

"'

..I

ct

a:

w

:z

w

:::.

a

"

C,

"'

<)

I-

w

..,

8

....

a:

I-

w

..,

I-

a.

ct

::c

(.)

..!!!

~

c...

7'

.....

OVERALL

WIDTH

27.6(700)---I

GROUND

LEVELIW/0

RIDER

i---------31.5(800,\------------<

'

r7-9

(200)

'

M

"'

) WHEELBASE

41

5{1.055) I

----j

>----------------<JVERALLENGTH

62.0(1.575)>------+-----4-,

DIMENSIONS/PROFILES TYPICAL

FOR

ALL

MODELS

0

~

e

N

,ri

N

I

"

I

Front fork

Chain

guard

Muffler

Side stand

magneto

Sprocket

Rear

wheel

Tail light (JT!L

Light

Rectangular)

<...

-I

~

r

<...

-I

"'

!1c!

i

,,

~

;,

1-3

Specifications & Performance

JT2

GENERAL-Specifications

and

Performance

Model

Dimensions .

Overall length Overall width Overall height Wheelbase

Mm

ground clearance

Weight,

Performance ·

Engine

Grr:iss

Fuel consumption

(on paved level roads) Climbing ability Min. turning radius Braking distance

Model Type 2 stroke,

Lubricating system Separate Cylinder

Displacement

Bore x Stroke 1

Compression

Max Max

Starting system

Ignition system Magneto Ignition timing

Carburetor

ratio power torque

Type M J

J N

Air cleaner Transmission

Clutch

Primary reduction system Primary reduction ratio 3.895

I

YAMAHA

62.4

in

( 1580 mm)

27 6 ,n ( 366

41.5

60

63

kg

,n (

,n

700

930

(1055

(160

1321bs

mm

mm) mm) mm)

)

176m1le/9al (19 mph)

22

degrees

59.1

24

in. (1,500

6

ft/22

mm)

mph

(7 5 m/35

JT1

gasoline lubricahon

Single. forward inclined.

3,54

654

6.4

1

cu

,n

in

x 1

(58

654

(YAMAHA

cc)

in_

(42

4.5 hp/7.500 rp.m 3

62ft-lb/5.500 r p.m

Kick starter

1gmt1on

18

mm

BTD.C

(See

3-19-C)

Corb.

Specs.

Wet .

foam

rubber

. multiple-disk

Wet

Gear

(74/19)

60

JT2

<62.0>

km/h)

Autolube)

mm

x

42

mm)

(0 5 k9-m/5.500

<JTI>

rpm)

-3-

GENERAL-Specifiaations

and

Performance

Model

Gear

box

Type Constant

system.

1st

2nd 3rd 4th

front

Reduction ratio

Secondary reduction system Secondary reduction ratio 011

capacity

Chassis

Frame Tubular-Double loop Suspension Suspension system. rear Swmging arm

Cushion system

Cushion system. rear

Steering system

Steering angle Caster Tra1!

Brakmg system

Type of brake Operation Operation system. rear

Tire size

Front Rear

Dynamo

Model

Manufacturer

Tanks

Gasoline tank capacity

011

tank capacity

3077(40/13)

1.889 I

1.038

Chain

3153(41/13)

0.85

T

elescop1c

Coil Coil

4 7° both right

63

2 7 in

Internal expansion Right Right foot operation

2 2

F11-L46 HITACHI

11 11

mesh,

(34/18)

304 ( 30/23)

(27/26)

US

qts

sprmg. oil damper sprmg,

5°

(68mm)

hand

50-t5-4PR 50-t5-4PR

ltd

gals(43/)

us

qts (1.0

YAMAHA

4-speed forward

(800-850

fork

011

damper

and

left

operation

<Fl

I)

60 JT2

cc)

1-L42>

-4-

1-4

PERFORMANCE

60

JT

5

ENGINE

I I

Maximum

Ma;ii;imum

CURVES

PERFORMANCE

4.5

3.62

I

B

1-P

Power

Torque

CURVES

I I

/7,500

rpm

ftlbs/5,S00rpm

Horse power

I

GENERAL·

Performance Curves

w

IQ

0

:i:

/

\

'

/ \

I'--..

\

',

'

\

w ~

:,

.

0

"'

3

"'

I

0

"'

...

-

2

~

I

r

I

Torque

------

........_

3

V

/

I

z

0

500

400

300

ii'

"

~

::,

i

~

8

~

J

~

View

I

/

'"'

2,000

----

3.000

Fuel consumption

4,000

5,000

ENGINE SPEED

6,000

7,000

8,000

(rpm)

3-port Cylinder

--

9,000

Exploded

-

10,000

(~-ti~)_

-N-/----<,----'---'--/---';-----''------\._

I I

-------

Exhaust port t ran sf er

22.0

24.0 \

---------

0

N

"'

":

~

"'

l , I

--------

- 5 -

par

19.5

0

"'

I

)

I

·~

-

'

__

Inlet port

-

,._,.

I

,_

____

1l

,~---~'---

"'

<D

~

0

~

<D

GENERAL-Tools

1-6

Tools

The

following

1

General

Tools

and Instruments for Shop Service

and

Instruments for

tools

and

instruments

1) Plug wrench 23x29

2)

A set

of

3) A set

4)

Plastic tip

5)

Steel

6)

Circlip pliers

7)

Circlip pliers

8)

Needle

9)

Pliers

10) Phiilips-head screwdriver It)

Phillips-head

12) Phillips-head screwdriver (M)

13) Phillips-head screwdriver (S)

wrenches

of

socket wrenches

hammer

(ST

(RT

nose

pliers

screwdriver(l)

Shop

are

required to service

mm.

type)

14) Slot-head screwdriver(M)

15) Slot-head screwdriver

16) T-handle socket

(S)

wrench

Service

Fig 1-6-1

the

JT2

2

Special

In

addition

3 Other

Tools

and

Instruments

I Clutch holding 2 Crankcase disassembling 3 Crankshaft 4 Flywheel 5 Flywheel

an

electro-testor, tachometer.(engine

Material

1)

Yamaha Bond (No.5)

2)

Gear

3)

Grease

4) Wiping material

5)

Yamaha Bond No.4

6)

Wood0J1

7)

Oiler

8) Oil jug

assembling

magneto

011

box

tool

holding

puller

tool

rpm

F,g

t-6-2

meter)

hy..drometer

,etc. should

and

available.

The

use

of a wooden

photo

will facilitate Consumable ment

parts

must

(such

also

box

engine

as

be

as

shown

service

gaskets)

on

hand.

in and

and

the

above

overhaul.

replace-

-6-

Fig.

1-6-3

YAMAHA

AUTOLUBE·What

is Yamaha

Autolube?

Features of Yamaha Autolube, Handling of the Oil Pump

CHAPTER

(

Automatic,

2

-1

What

is

Yamaha

Conventional 2-stroke engines are lubricated

mixed

in

gasoline. but

automatic, separate lubrication system, That

in

a separate oil tank

oil

pump

and

fed

to

speed

and

load

Autolube?

YAMAHA

is

the

·s

Autolube furnishes

automatically regulated

engine

according

2

YAMAHA

Separate

by

oil pre-

an

1s.

the oil

by

the

to

engine

AUTOLUBE

lubrication

YAMAWI

AlJTOLUBE

OIL

•.

iiij;~

Fig 2-1-1

Sys

STRAIGHT

tern)

~IN£

2-2

Features

The

oil

pump

which

in

turn

according to engine speed and throttle valve opening, thus pumping the optimum amount of oil for under any operating condition.

This "automatic. separate lubrication" does not merely eliminate disadvantages

11

further improves the perform,,nce and efficiency of

which formerly existed

The

Autolube feeds

featuring .

1s

dnven

is

controlled

of

Yamaha

Autolube

by

the

engine

through a reduction gear

by

the

occellerotor grip The

an

optimum amount of lubricating oil to the engine under any operating condition, thus

oil

2-stroke

,and

is

connected

pump

automatically regulates

designs by eliminating certain oil-starvation conditions

to

the

in

the conventional

carburetor throttle

the

volume

* Less oil consumption

* Less carbon accumulation * Less exhaust smoke

* Improved lubricating efficiency.

2

The

Auto[ube simplifies fuel supply. thus featuring:

* Using straight gasoline directly

in

the gas

tank

* Less fuel contamination.

3 The Auto!ube improves the reliability of lubrication. thus eliminating.

* Special care concerning oil/fuel mixing ratios.

2

-3.

Handling the

The oil pump is a precision-machined assembly.

from the engine. protect handling will keep the pump free from trouble.

Oil

Pump

Make

no

attempt to disassemble

1t

from dust dirt. ·etc,. and after reinstalling lt. bleed and adjust the pump correctly. Proper

it.

When

you

remove the oil pump

of

engi_ne

pre-mix

cable,

lubricating oil

!ubncation

system. but

-7-

YAMAHA

AUTOLUBE·Handling

of

the

Oil

Pump

The oil pump is similar ment

of

a

4,0

in

¢ plunger.

both construction

and

operation to other Autolube

2-3-1 Checking Minimum Pump Stroke

1 Checking

a Fully close

b Turn the oil pump starter plate in

of the arrow marked

the gap between the adjustment pulley and the adjustment plate. Keep as

possible

to measuring,

c.

Insert a feeler gauge

If

the

...... Stroke

If

the

...... Stroke

qap

gap

the

accelerator grip.

on

by

observing lt with

(015

allows it

Is

does

is

to

correct

not allow

insufficient

the

direction

the plate. Then measure

the

gap

as

the

eye prior

mm) into

enter

the

wide

gap

Fig 2-3-1

systems.

The only difference

is

the

employ-

2 Adjustment

a Remove

then

the

remove

adJustment

the

adjustment plate

plate lock

nut.

and

-8-

Fig

2-3-2

2-3-3

YAMAHA

AUTOLUBE·Handling of the

Oil

Pump

b Install a O 1

adJustment plate was

c Reinstall

measure minimum stroke When the gap allows a O 20 not allow a O 25

adiusted

Stroke adJustment tolerance .... Q.20 to

2-3-2

Follow pump

Carburetor

and

I I Throttle

a AdJust

9 To bring

• To check this adiustment lightly pull throttle

mm

adiustment shim where the

the

adjustment plate lock

mm,

feeler gauge

mm.

and

the

preceedmg

carburetor

Cable

Adjustment

td!e.

from

correct adJustment. loosen or tighten the throttle cable adiustment screw

cable

increase

in

section

as

described m the

the

carburetor

and

remove all but 1

cable B

the

play

B.

and engine speed should slightly

from

1dlmg r.p.m. after 1

to

the stroke

Autolube

2-3-1

with

of

the throttle cable into

nut.

enter but does

1s

correctly

0.25

CiJble

steps

the engine

mm

of slack

of travel.

and

mm.

Fig

Adjustment

to

check minimum stroke. below

at

Fig

mm

2-3-4

2-3-5

and

adJust

Throttle

11

1f

incorrect Then

cable

8 Adjusting play cable

B to 1 mm,(0,04 in.)

Look nut

of

the throttle

ad1ust

the

b Next.

adJust

gap

as

shown

between 0,5

throttle

in

Fig

and

1 0

cable(A)

2-3-6

mm

(0

so be!ow 02

,..__,0

that

e Check the p!ay of the throttle cable

by

pu!hng

on

the outer part of the throttle

cable If the play

ad1ust

the play using the odiustor.

1s

excessive or

msuff1cent.

w1!!

04

the

(A)

bE

in~

-9-

Fig

Throttle

2-3-6

cable(A)

Cable

Adjustor

guide(A)

+-landle

Lock nut

grip

ENGINE·

2)

Handling

Autolube

of

the

Cable

Oil

Pump

Adjustment

With the throttle cable properly adjusted, check the pump guide pin location. It should be no closer

(.060") close, loosen adjusting bolt until adjustment

to

the raised boss

the

lock

of

the pump pulley.

nut

(see Figure 2-3-7) and

is

correct.

than

If

it turn Tighten

lock nut.

1.5mm is

too

the

Lock

nut

Next, turn throttle

to

full open position, the guide pin

should not strike the raised boss

position,

if

it does, loosen the adjusting bolt slightly

provide clearance.

2-3-3

Bleeding

When

the

pump

has

been removed or the Autolube oil

an

irregular flow

ular flow of oil.

I ) Remove the bleeder bolt.

of

oil

after

b'

leed the pump

the

of

the pump pulley

pump

1s

mounted again

in

the

following manner

or

in

has

the

this

to

run

01!

Fig

2-3-7

out.

air will enter the pump. The air will cause

tank

1s

refilled

In

order

to

prevent such

an

irreg-

Guide

2)

Next. rotate

the arrow marked

mg

011

and

this and stroke becomes greater, the air can

the

starter plate

on

the

plate until tighten the bleeder bolt To facilitate

bleeding,

rotate!

no

fully

open

the

starter plate. As

in

the

plate. Continue turn-

air comes out with

the

accelerator

bled.

direction of

the

grip

the

plunger

be

quickly

-10

Fig

Fig 2-3-9

-

2-3-8

ENGINE-Engine Removal

CHAPTER

This chapter service data. However, except when overhauling and oil seals

save a lot

Preparation

1)

All

before removal and disassembly. This will prevent

engine assembly.

2)

Before engine removal form a clean

3)

During disassembly of the engine assembly time faster and easier,

3

-1

c;lescribes

in

of

time

dirt.

mud,

Engine

Start the engine then

turn off the engine and drain the transmission

oil

the disassembly and reassembly of the engine, its removal from the chassls, and the necessary

the crankcase, it

and

labor.

for

disassembly

dust.

and

·efficient job.

and

is

suggested that engine

of the engine :

foreign

material

disassembly,

..

clean all parts and place them

and

insure correct installation of all engine parts.

Removal

and

warm it up for a few

3 ENGINE

the

crankshaft assembly, transmission, shifter mechanism or bearings

be

should

be

sure

.minutes,

serviced without removing

be

thoroughly

any

you

have

removed

harmful foreign material from entering the interior of the

proper tools and cleaning equipment

in

trays

from

in

it

from the chassis. This will

the

exterior

of

the

engine

so

order of disassembly. This will make

you

assembly

can

per-

(Volume of o;I

2 Pull out the seat fitting

by pulling

it

800-850

YAMALUBE

SAE

lOW-30

backward.

cc

10.85

US

4-CYCLE

or

"SE"

and remove the seat

qt)

Fig

3-1-1

3-1-2

-11-

ENGINE·

Engine

Removal

3 Disconeect

tank.

Remove

lift

the fuel

4

Remove

and remove the plug

the connector from

the

the tank

tank

fuel

off.

line

mounting

cap,

at

the

bottom of the

bolt (13) and

magneto

lead

fuel

wire

F,g

3-1-3

5

Remove a)

Use only damage

Remove

the

the muffler

special

b)Remove

(13

the

exhaust pipe

wrench. Hammering on

it

and/or

the

cylinder.

the

muffler holding bolts

mm)

nut.

the

nut will

Fig

3-1-4

3-1-5

-12-

Fig

3-1-6

6

7

Remove

the

change pedal

(10

mm)

the

!efthand crankcase cover

($

screwdriver)

Fig

ENGINE-Engine Removal

3-1-7

8 Disconnect the master link and remove the

When reconnecting the chain be sure the master link

driving

After reconnecting the chain adjust the free play to section

with

the rear wheel

on

the ground.

chain.

direction

Fig

3-1-8

Fig

3-1-9

is

facing

in

the correct direction.

25

mm.

( 1 in.) up and down at the center

of

the lower

-13-

ENGINE-Engine Removal

9

10

Remove

Remove bolt

to

the

((£)

the

stop

pump cover

screY_tdriver)

oil

pipe

the

flow

and

of

and

plug

oil.

pump cable

the

from

the

hole

tank

Fig 3-1-10

with a

12.

Remove

the

fuel line

(8

the

four engine mounting bolts

and

screwdriver)

(13 mm)

remove

the

carburetor

Fig

3-1-11

Fig 3-1-12

Fig 3-1-13

Fig 3-1-14

-14-

13

Remove

3

-2

Cylinder

A

Note: During reassembly the head bolts must be torqued

The cylinder

Removing

Remove

sequence for rernsta!lation, Replace

torque a

the

hot

the

Head

four

engine

head

special

from

the

frame.

is

bolted

on

the

cylinder with special

nuts

from

the

top

of

the

gasket. if damaged or

(10

mm)

and

for

most accurate readings_ place a small amount of light we;ght oil

cylinder

to

90

Fig 3-1-15

nuts.

head,

then

in

questionable condition.

rn/lbs

rn

the

head

pattern, and

ENGINE·

Cylinder Head

and

head

gasket

Reverse

in

successive stages. Do not

on

the threads first.

the

Fig 3-2-1

8

Removing

Carbon

chamber

increase ignition

Scr~pe

Use

o rounded

num.

Carbon

deposits

and

in

the

and

engine

the

cylinder

Deposits

on

the

top of

the

compression

overheating

head

scraper

to ovoid damaging

cylinder

piston

ratio,

and

head

will

as

.

piston

combustion

result

well

as

dome

clean.

the

in

an

pre-

olumi•

-15-

Fig

3-2-2

3-2-3

ENGINE·

Cylinder

3-3

Cylinder

A

1)

2)

Remove with a soft faced hammer.

Always replace

when reassembling.

the cylinder

the

by

cylinder

striking

base

it

gasket

lightly

Fig 3-3-1

8 Checking the Cylinder for

1) Measure

gauge. (Measure it at

angles

(0.0019")

the

amount of wear of the cylinder wall with a cylinder bore measuring micrometer

to

the

crankshaft) If the difference between the

rebore

0

-s-

--

0

---------....

2)

The piston clearance between

Wear

and

four

hone

depths

while

the cylinder

0

the

Fig

3-3-2

posit1on1ng the instrument parallel. and then at riQht

maximum

and

minimum

diameter exceeds 0.05

a

b

D

-c

piston

and

the cylinder

1------1'-

d

is

0.040-:-0.045

mm

(0.0016"-0.0018")

or

cylinder

mm.

-

16-

C

Cylinder

ENGINE-Cylinder, Piston Pin

Reconditioning

1) Pistons

2)

are

available

The cylinder should

in

be

able clearance

3)

The error between

the

(0.0015")

4) If cylinder rebore is necessary, be sure

D

Removing

Scrape off

port

of

saw

blade

E Installing

and breaking

Carbon

the

cylinder with

the

on

o sharp port

Deposits

carbon accumulation

the

Cylinder

dulled

0.25 and 0.50

rebored

maximum

t::dge.

in

end

and

the

of

a hack-

exhaust

mm.

(0.01 Q"

honed

to

the

minimum diameters after

to

chamfer

and

diameter

all

port

Fig

0.020")

of

edges

3-3-3

oversizes.

the oversize piston plus

honing

should

to

prevent

be

the

no

the

more

rings

minimum allow-

than

0.04

mm.

from

catching

Put

your

fingers at expand the both

ends

of rmg groove. Next. slip the cylinder down over the piston. Compress the rings

breakage

3

-4

A Pulling out the Piston

Remove with needle with a finger Note : Before removing the piston

the crankcase with a accidentally drop

into

during

Piston

the clips at both ends

nose

the

crankcase.

each

end

of

ring,

and

slip

it

onto

the

ring with the knock

installation.

pliers,

and

press

or

a slot-head screwdriver.

clean

rag.

the

clip

or

other foreign particles

the

piston

the

piston.Align

pin m eac:h

to

prevent ring

of

the

piston

out

the piston pin

clips, cover

so

you

will

ring.

not

Fig

3-3-4

Fig 3-4-1

-17-

ENGINE·

Piston

Ring

B Piston•to-Piston

The piston pin should fit snugly

replace

If

the pin

end

F,g

3-4-2

3-5

Piston

A

Removing

Put your thumbs at Remove

the

has

step-wear m

of the connecting rod for wear

Ring

the Piston

the

nng

fit

in

its bore

and/or

the

piston

I1s

center, replace

by

Rings

each

end

of

the

piston ring

by

moving the ring off the piston

so

the

inserting

that it drags a

needle bearing

the

piston

Fig

3-4-3

and

pull

the

on

the other

htt!e

as

well

and

bearing

piston ring

side

of

you

turn

as

the

ends

the ring

1t.

piston

apart

ends

If the piston

pm,

Check the

and

lifting

up.

is

loose

small

F,g 3-5-1

B Installing

the

Piston

First

flt

No.2 nng

No

1 ring.

and

align their ing pin The printing

in

ec> · ru~'"g

on

the gap properly

Rings

over

the

end

groove.

a11

, lngs must face

at

the pin

piston.

and

gaps with

(Fig.

3-5-3) up

then

the

to

position

the

locat-

-18-

Fig

3-5-2

3-5-3

1rst

Second

Locating

/

,

knock

~

Piston ring

C.

Checking the Piston

1)

Measuring piston ring wear ,Put the ring into

the

cylinder so that cylinder bottom end

gap with a feeler gauge(Fig

The

end

gap should

mm.

(0.006---0.014")

rings

2)

Removing carbon

Carbon

on

blow -by

Remove the rings end

of

an

3-6

Piston

The piston

edge.

the

piston rings

old

ring'

is

made

Rings

the

ring

is

and

then

be

between

for

both

No.1

and

from

the piston. and clean the carbon from the rings and

as

a scraper.

of

a high-silicon aluminum

parallel

to

the

measure

·3-5-4)

0.t5

in

the

and

0.35

and

No.2

ring grooves will make

alloy.

Fig.

3-5-4

the

rings stick

in

the

piston. thus causing gas

ring

grooves.

ENGINE

-Piston

using

the

A Checking

1)

2)

and

Correcting the Piston to Cylinder

Measuring piston clearance

Piston

clearance

the

minimum maximum described should

To determine measure angles bottom

Checking

piston

A piston showing signs

in cause

If

without correction ,another seizure will develop in

"high spot"

sand paper

outside diameter

be

0.040-0.04Smm

the

to

the

edge.

noise

and

damage

a piston that

the

same

is

the

difference between

cylinder bore diameter

of

the

in

4-3

Cylinder, piston clearance

(0

0016-0.0018")

the

maximum

piston with a micrometer at right

skirt

10

(Fig

3-6-1)

and

correcting scratches

loss

of engine power. It will also

to

the

has

area.

Lightly sand

on

the piston with wet #400

until

smooth.

piston diameter,

mm.

(3/8

of

seizure will result

cylinder wait

seized

is

Wall

and

the

piston As

in.) from its

on

the

used

again

the

seizure

Clearance

Fig.

3-6-1

-19-

Fig

3-6-2

ENGINE-Piston

3)

Removing Carbon Remove carbon head,

Note Whenever carbon accumlat1ons are removed,

take care that the under lying metal

Flywheel

using a screwdriver or a saw-blade

Magnet

accumulqt1ons

on

the

piston

1s

not

scored or otherwise damaged

F,g

3-6-3

Carbon and ring grooves will result

Remove them from the ring groove

gum

accumulations

B Piston Installation Direction

Install

the

piston with the arrow mark

pointing forward (toward

cylinder)

in

the

in

piston ring seizure

on

the

exhaust port of

piston

the

head

the

Fig

3-6-4

3

-7

Flywheel Magneto

A Remove the

ho!dmg

socket

tool

to

loosen it.

nut

using a flywheel

to

hold the magneto and a

magneto

19

mm

-20-

Fig

3-6-5

F,g 3-7-1

B

In

sta!l

Then break loose.

C

Remove neto

wheel magneto

the

flywheel magneto puller

tighten

base

the

bolt.

(left-hand

(Nut:

17

mm)

the

two screws holding

to

the crankcase,

base

The flvvvheel

thread)

the

and

magneto

flywheel mag-

remove

the

will

fly-

Fig

ENGINE·

3-7-2

Flywheel Magneto, Crankcase Cover

D

Remove It flywheel magnets (using its magnetic force) while the

keep it from becoming

3-8

A

Removal

1)

the

woodruff

is

advisable to place

key

is

removed

(0Screw

Crankcase

Remove

crank.

the

(10

key,

the

woodruff key

for

engm

e service

lost

driver, hammer)

Cover

(R.H.)

kick crank mounting bolt

mm)

This

and

on

the

will

the

Fig

3-7-3

3-7-4

-21-

Fig

3-8-1

ENGINE-Crarkcase Cover,

2)

Remove

crankcase cover.

taking

Note:

the

seven

pan

cover,

and

( The cover

off

the

oil

pump.)

In

this case, be sure

Autolube

pump

cover removal.

3)

Remove

it.

the crankcase cover gasket .Replace

if

damaged.

Clutch

head

screws holding the

then

remove the case

can

be

banjo

removed

to

pull

bolt

without

out

before

the

Fig

3-8-2

B Installation Fig

Spread

YAMAHA

face of

the

gasket

on

the

No.5

and

to

apply

YAMAHA

face : otherwise Note : When

make ,re that the pump drive gear ( from sYnthetic resin) with the primary drive

make certain that all mating surfaces

been

3-9

Clutch

The clutch It

is The This reduction gear

installed

clutch

is

of the wet disc type, consisting of two molded cork friction plates on

housing

Bond

No.5

over

the

crankcase R Place

crankcase

install the crankcase cover

Bond

the

crankcase will leak

ir

'alling the crankcase cover

thoroughly cleaned

the transmission main shaft.

forms a

is

in mesh

the

crankcase cover

and

apply Yamaha Bond

No.5

to

the

1s

correctly engaged

gear_

In

one

piece assembly

with

the primary drive gear. The primary

mating sur-

R.

Be sure

mating

sur-

(R) made

addition,

have

Fig

with

the primary driven gear

3-8-3

3-8-4

and

of

reduction

one steel clutch plate.

the onmarv reduction

ratio

is

74/19

(3.894).

system.

-22-

ENGINE-Clutch

1.

Primary driven gear ass y

2.

Thrust plate

3.

Clutch boss

4. Clutch plate

5.

Friction plate

6.

Pressure plate

7.

Clutch spring

8. Spring screw

9.

Push rod t

10.

Lock

nut

11.

Lock

washer

12.

Spacer

13.

Thrust plate

14.

Ball

15.

Push rod 2

16.

Kick pinion gear

Fig

3-9-1

Clutch

ass'y

exploded view

A.

Removing

Remove the four clutch spring holding screws, and take out the pressure plate and push crown.

Fig.

3-9-2

the

Pressure

( 8

Plate

Screwdriver)

Fig.

3-9-3

-23-

ENGINE·

Clutch

B.

Removing the Clutch Boss Install the clutch holding tool

Loosen the lock

C.

Checking the Clutch Spring If

the

free length of the spring is 1

more shorter

nut.

and then remove the clutch

(19

mm)

than

the standard free length, replace

(Slide

calipers)

on

the dutch

mm.

boss.

(0.04

boss.

in.) or

Fig

3-9-4

it.

Free length

D.

Checking the Friction Plates Measure the fnct1on plate at several

Replace it

or

more. Also replace

evident.

Standard thickness= 3.5 mm. (0.137 in.)

Wear

34

if

(Slide

limit=

3.15

3.5

mm(Standard

it

is

mm.

worn

mm

(1.340

more

11

calipers)

(0.124

Thickness)

m)

than

1f

uneven

in.)

points

for

wear.

0.35mm.(0.0137in.)

contact

1s

quite

(

I

Fig.

3-9-5

3-9-6

-

24

--

Yamaha JT2M (1972), JT1 (1971), JT1L (1971), JT2 (1972) Service Manual

Specifications and Main Features

Frequently Asked Questions

User Manual