JUKI MO-6800S Series Quick start guide

40159525
No. E419-02
ENGINEER’S MANUAL
High-speed, Overlock/Safety Stitch Machine
MO-6800S Series

PREFACE
This Engineer’s Manual is written for the technical personnel who are responsible for the service and
maintenance of the machine.
The Instruction Manual for these machines intended for the maintenance personnel and operators at
an apparel factory contains operating instruction in detail. And this manual describes “Standard Adjust-
ment”, “Adjustment Procedures”, “Results of Improper Adjustment”, and other important information
which are not covered in the Instruction Manual.
When carrying out the maintenance work on the sewing machine, be sure to refer also to the Instruction
Manual and the Parts List.
In addition, for the motor for the sewing machine with thread trimmer, refer to the separate Instruction
Manual or This manual gives the “Standard Adjustment” on the former page under which the most basic
adjustment value is described, and on the latter page “Results of Improper Adjustment” under which
stitching errors and troubles arising from mechanical failures and “How to adjust” are described.

i
For the sewing machine, automatic machine and ancillary devices (hereinafter collectively referred to as
"machine"), it is inevitable to conduct sewing work near moving parts of the machine. This means that there
is always a possibility of unintentionally coming in contact with the moving parts. Operators who actually
operate the machine and maintenance personnel who are involved in maintenance and repair of the machine
are strongly recommended to carefully read to fully understand the following Safety precautions of this
engineer's manual before using/maintaining the machine. The content of the Safety precautions of this
engineer's manual includes items which are not contained in the specications of your product.
The risk indications are classied into the following three different categories to help understand the meaning
of the labels of this engineer's manual and the product. Be sure to fully understand the following description
and strictly observe the instructions.
( I ) Explanation of risk levels
( II ) Explanation of pictorial warning indications and warning labels
Warning label
❶
❷
❸
❶
• There is the possibility that slight to serious injury or death may be caused.
• There is the possibility that injury may be caused by touching moving part.
❷• To perform sewing work with safety guard.
• To perform sewing work with safety cover.
• To perform sewing work with safety protection device.
❸
• Be sure to turn the power OFF before carrying out "machine-head threading,"
"needle changing," "bobbin changing" or "oiling and cleaning.
❸
❷
❶
Electrical-shock
danger label
DANGER :
This indication is given where there is an immediate danger of death or serous injury if the person in charge or any third
party mishandles the machine or does not avoid the dangerous situation when operating or maintaining the machine.
WARNING :
This indication is given where there is a potentiality for death or serious injury if the person in charge or any third party
mishandles the machine or does not avoid the dangerous situation when operating or maintaining the machine.
CAUTION :
This indication is given where there is a danger of medium to minor injury if the person in charge or any third party
mishandles the machine or does not avoid the dangerous situation when operating or maintaining the machine.
Items requiring special attention
Pictorial warning indication
There is a risk of injury if contact-
ing a moving section.
Pictorial warning
indication
Be aware that holding the sewing
machine during operation can
hurt your hands.
There is a risk of electrical shock if
contacting a high-voltage section.
There is a risk of entanglement
in the belt resulting in injury.
There is a risk of a burn if contact-
ing a high-temperature section.
There is a risk of injury if you
touch the button carrier.
Be aware that eye deciency can
be caused by looking directly at
the laser beam.
Indication label
The correct direction is indicat-
ed.
There is a risk of contact between
your head and the sewing ma-
chine.
Connection of a earth cable is
indicated.
TO ENSURE SAFE USE OF YOUR SEWING MACHINE
Adjustment :
It means replacement of parts,
disassembly, and repair assembly.

ii
Basic precaution
1. Be sure to read the engineer's manual and other explanatory documents supplied with accessories of
the machine before using the machine. Carefully keep the engineer's manual and the explanatory docu-
ments at hand for quick reference.
2. The content of this section includes items which are not contained in the specications of your product.
3. Be sure to wear safety goggles to protect against accident caused by needle breakage.
4. Those who use a heart pacer have to use the machine after consultation with a medical specialist.
5. Turn OFF the power before starting the work in order to protect against accident that can result in per-
sonal injury.
If it is inevitable to carry out work with the power ON, utmost care should be taken to prevent from de-
pressing the foot pedal or pressing the start switch by mistake.
6. Make sure, after the completion of replacement work, that neither connectors nor cables are damaged,
slipped off or loosened in order to protect against accident that can result in personal injury.
Safety devices and warning labels
1. Be sure to operate the machine after verifying that safety device(s) is correctly installed in place and
works normally in order to prevent accident caused by lack of the device(s).
2. If any of the safety devices is removed, be sure to replace it and verify that it works normally in order to
prevent accident that can result in personal injury or death.
3. Be sure to keep the warning labels adhered on the machine clearly visible in order to prevent accident
that can result in personal injury or death. If any of the labels has stained or come unstuck, be sure to
change it with a new one.
Application and modication
1. Never use the machine for any application other than its intended one and in any manner other than that
prescribed in the engineer's manual in order to prevent accident that can result in personal injury or death.
JUKI assumes no responsibility for damages or personal injury or death resulting from the use of the
machine for any application other than the intended one.
2. Never modify and alter the machine in order to prevent accident that can result in personal injury or death.
JUKI assumes no responsibility for damages or personal injury or death resulting from the machine
which has been modied or altered.
Education and training
1. In order to prevent accident resulting from unfamiliarity with the machine, the machine has to be used
only by the operator who has been trained/educated by the employer with respect to the machine oper-
ation and how to operate the machine with safety to acquire adequate knowledge and operation skill. To
ensure the above, the employer has to establish an education/training plan for the operators and edu-
cate/train them beforehand.
Items for which the power to the machine has to be turned off
Turning the power off: Turning the power switch off, then removing the power plug from the outlet. This
applies to the following.
1. Be sure to immediately turn the power off if any abnormality or failure is found or in the case of power
failure in order to protect against accident that can result in personal injury or death.
2. To protect against accident resulting from abrupt start of the machine, be sure to carry out the follow-
ing operations after turning the power off. For the machine incorporating a clutch motor, in particular,
be sure to carry out the following operations after turning the power off and verifying that the machine
stops completely.
2-1. For example, threading the parts such as the needle, looper, spreader etc. which have to be thread-
ed, or changing the bobbin.
2-2. For example, changing or adjusting all component parts of the machine.
2-3. For example, when inspecting, repairing or cleaning the machine or leaving the machine.
3. Be sure to remove the power plug by holding the plug section instead of the cord section in order to pre-
vent electrical-shock, earth-leakage or re accident.
4. Be sure to turn the power off whenever the machine is left unattended between works.
5. Be sure to turn the power off in the case of power failure in order to prevent accident resulting of break-
age of electrical components.
PRECAUTIONS TO BE TAKEN IN VARIOUS OPERATION STAGES
Accident means "to cause
personal injury or death or
damage to property."
CAUTION
DANGER
SAFETY PRECAUTIONS
1. When it is necessary to open the control box containing electrical parts, be sure to turn the power off and
wait for ve minutes or more before opening the cover in order to prevent accident leading to electrical
shock.

iii
Transportation
1. Be sure to lift and move the machine in a safe manner taking the machine weight in consideration. Refer
to the text of the engineer's manual for the mass of the machine.
2. Be sure to take sufcient safety measures to prevent falling or dropping before lifting or moving the
machine in order to protect against accident that can result in personal injury or death.
3. Once the machine has been unpacked, never re-pack it for transportation to protect the machine against
breakage resulting from unexpected accident or dropping.
Unpacking
1. Be sure to unpack the machine in the prescribed order in order to prevent accident that can result in
personal injury or death. In the case the machine is crated, in particular, be sure to carefully check nails.
The nails have to be removed.
2. Be sure to check the machine for the position of its center of gravity and take it out from the package
carefully in order to prevent accident that can result in personal injury or death.
Installation
(I) Table and table stand
1. Be sure to use JUKI genuine table and table stand in order to prevent accident that can result in personal
injury or death. If it is inevitable to use a table and table stand which are not JUKI genuine ones, select the
table and table stand which are able to support the machine weight and reaction force during operation.
2. If casters are tted to the table stand, be sure to use the casters with a locking mechanism and lock
them to secure the machine during the operation, maintenance, inspection and repair in order to prevent
accident that can result in personal injury or death.
(II) Cable and wiring
1. Be sure to prevent an extra force from being applied to the cable during the use in order to prevent electri-
cal-shock, earth-leakage or re accident. In addition, if it is necessary to cable near the operating section
such as the V-belt, be sure to provide a space of 30 mm or more between the operating section and the cable.
2. Be sure to avoid starburst connection in order to prevent electrical-shock, earth-leakage or re accident.
3. Be sure to securely connect the connectors in order to prevent electrical-shock, earth-leakage or re
accident. In addition, be sure to remove the connector while holding its connector section.
(III) Grounding
1. Be sure to have an electrical expert install an appropriate power plug in order to prevent accident caused
by earth-leakage or dielectric strength voltage fault. In addition, be sure to connect the power plug to the
grounded outlet without exceptions.
2. Be sure to ground the earth cable in order to prevent accident caused by earth leakage.
(IV) Motor
1. Be sure to use the specied rated motor (JUKI genuine product) in order to prevent accident caused by
burnout.
2. If a commercially available clutch motor is used with the machine, be sure to select one with an entan-
glement preventive pulley cover in order to protect against being entangled by the V-belt.
Before operation
1. Be sure to make sure that the connectors and cables are free from damage, dropout and looseness be-
fore turning the power on in order to prevent accident resulting in personal injury or death.
2. Never put your hand into the moving sections of the machine in order to prevent accident that can result
in personal injury or death.
In addition, check to be sure that the direction of rotation of the pulley agrees with the arrow shown on
pulley.
3. If the table stand with casters is used, be sure to secure the table stand by locking the casters or with
adjusters, if provided, in order to protect against accident caused by abrupt start of the machine.
During operation
1. Be sure not to put your ngers, hair or clothing close to the moving sections such as the handwheel,
hand pulley and motor or place something near those sections while the machine is in operation in order
to prevent accident caused by entanglement that can result in personal injury or death.
2. Be sure not to place your ngers near the surround area of the needle or inside the thread take-up lever
cover when turning the power on or while the machine is in operation in order to prevent accident that
can result in personal injury or death.
3. The machine runs at a high speed. Never bring your hands near the moving sections such as looper,
spreader, needle bar, hook and cloth trimming knife during operation in order to protect your hands
against injury. In addition, be sure to turn the power off and check to be sure that the machine complete-
ly stops before changing the thread.
4. Be careful not to allow your ngers or any other parts of your body to be caught between the machine
and table when removing the machine from or replacing it on the table in order to prevent accident that
can result in personal injury or death.
5. Be sure to turn the power off and check to be sure that the machine and motor completely stop before re-
moving the belt cover and V-belt in order to prevent accident caused by abrupt start of the machine or motor.
6. If a servomotor is used with the machine, the motor does not produce noise while the machine is at rest.
Be sure not to forget to turn the power off in order to prevent accident caused by abrupt start of the motor.
7. Never use the machine with the cooling opening of the motor power box shielded in order to prevent re
accident by overheat.

iv
Lubrication
1. Be sure to use JUKI genuine oil and JUKI genuine grease to the parts to be lubricated.
2. If the oil adheres on your eye or body, be sure to immediately wash it off in order to prevent inamma-
tion or irritation.
3. If the oil is swallowed unintentionally, be sure to immediately consult a medical doctor in order to pre-
vent diarrhea or vomiting.
Maintenance
1. In prevention of accident caused by unfamiliarity with the machine, repair and adjustment has to be car-
ried out by a service technician who is thoroughly familiar with the machine within the scope dened in
the engineer's manual. Be sure to use JUKI genuine parts when replacing any of the machine parts. JUKI
assumes no responsibility for any accident caused by improper repair or adjustment or the use of any
part other than JUKI genuine one.
2. In prevention of accident caused by unfamiliarity with the machine or electrical-shock accident, be sure
to ask an electrical technician of your company or JUKI or distributor in your area for repair and mainte-
nance (including wiring) of electrical components.
3. When carrying out repair or maintenance of the machine which uses air-driven parts such as an air cyl-
inder, be sure to remove the air supply pipe to expel air remaining in the machine beforehand, in order to
prevent accident caused by abrupt start of the air-driven parts.
4. Be sure to check that screws and nuts are free from looseness after completion of repair, adjustment
and part replacement.
5. Be sure to periodically clean up the machine during its duration of use. Be sure to turn the power off
and verify that the machine and motor stop completely before cleaning the machine in order to prevent
accident caused by abrupt start of the machine or motor.
6. Be sure to turn the power off and verify that the machine and motor stop completely before carrying out
maintenance, inspection or repair of the machine. (For the machine with a clutch motor, the motor will
keep running for a while by inertia even after turning the power off. So, be careful.)
7. If the machine cannot be normally operated after repair or adjustment, immediately stop operation and
contact JUKI or the distributor in your area for repair in order to prevent accident that can result in per-
sonal injury or death.
8. If the fuse has blown, be sure to turn the power off and eliminate the cause of blowing of the fuse and
replace the blown fuse with a new one in order to prevent accident that can result in personal injury or
death.
9. Be sure to periodically clean up the air vent of the fan and inspect the area around the wiring in order to
prevent re accident of the motor.
10. In order to prevent accidents resulting in personal injury or death, adjustments have to be carried out
within the instructions described in this Engineer's Manual and in the Instruction Manual by the person-
nel who have been well trained by the employer with respect to the latest knowledge and safety for the
machine.
11. Make sure that water is contained in cylinders and pipes, then remove water from them in order to pre-
vent accidents due to a malfunction of the machine.
Operating environment
1. Be sure to use the machine under the environment which is not affected by strong noise source (electro-
magnetic waves) such as a high-frequency welder in order to prevent accident caused by malfunction of
the machine.
2. Never operate the machine in any place where the voltage uctuates by more than "rated voltage ±10 %"
in order to prevent accident caused by malfunction of the machine.
3. Be sure to verify that the air-driven device such as an air cylinder operates at the specied air pressure
before using it in order to prevent accident caused by malfunction of the machine.
4. To use the machine with safety, be sure to use it under the environment which satises the following
conditions:
Ambient temperature during operation 5°C to 35°C
Relative humidity during operation 35 % to 85 %
5. Dew condensation can occur if bringing the machine suddenly from a cold environment to a warm one.
So, be sure to turn the power on after having waited for a sufcient period of time until there is no sign
of water droplet in order to prevent accident caused by breakage or malfunction of the electrical compo-
nents.
6. Be sure to stop operation when lightning ashes for the sake of safety and remove the power plug in
order to prevent accident caused by breakage or malfunction of the electrical components.
7. Depending on the radio wave signal condition, the machine may generate noise in the TV or radio. If this
occurs, use the TV or radio with kept well away from the machine.
8. In order to ensure the work environment, local laws and regulations in the country where the sewing
machine is installed shall be followed.
In the case the noise control is necessary, an ear protector or other protective gear should be worn ac-
cording to the applicable laws and regulations.
9. Disposal of products and packages and treatment of used lubricating oil should be carried out properly
according to the relevant laws of the country in which the sewing machine is used.

v
Transportation
1. Be sure to lift this machine with four or more workers and use a carriage for moving it in order to pre-
vent personal injury.
2. Be sure to take sufcient safety measures to prevent falling or dropping before lifting or moving the
machine in order to protect against accident that can result in personal injury or death.
3. Installation is described in the Instruction Manual. Be sure to fully understand the description before
putting the machine into operation.
Replacement of parts
1. In prevention of accident that can result in personal injury, be sure to carry out disassembly/assembly
work within the specied range given in this Engineer's Manual and in the Instruction Manual.
2. Turn OFF the power before starting the work in order to protect against accident that can result in per-
sonal injury.
If it is inevitable to carry out work with the power ON, utmost care should be taken to prevent from de-
pressing the foot pedal or pressing the start switch by mistake.
3. Be sure to carry out replacement work after having installed the machine in a stable state in order to
protect against accident that can result in personal injury.
In addition, be sure to select appropriate tools.
4. In prevention of accident that can result in personal injury, make sure, after the completion of adjust-
ment work, that neither screws nor nuts are loosened or come in contact with other parts.
5. Be sure to use JUKI genuine parts when replacing any of the machine parts.
JUKI assumes no responsibility for any accident caused by any part other than JUKI genuine one.
In addition, in the event you cannot replace parts within the specied range, immediately stop the re-
placement work and ask JUKI or distributor in your area for replacement of the parts.
Adjustment
1. Be sure to adjust according to the instructions given in this Engineer's Manual and in the Instruction
Manual in order to protect against accident that can result in personal injury.
2. Be sure to carry out replacement work after having installed the machine in a stable state in order to
protect against accident that can result in personal injury.
In addition, be sure to select appropriate tools.
3. In prevention of accident that can result in personal injury, make sure, after the completion of adjust-
ment work, that neither screws nor nuts are loosened or come in contact with other parts.
4. Turn OFF the power before starting the work in order to protect against accident that can result in per-
sonal injury.
If it is inevitable to carry out work with the power ON, utmost care should be taken to prevent from de-
pressing the foot pedal or pressing the start switch by mistake.
5. In prevention of accident that can result in personal injury or entanglement accident, be sure to ensure
safety at the time of test run. In addition, be sure to take care not to allow hair or cloths to come in con-
tact with the machine belt.
Disassembly/assembly
1. In prevention of accident that can result in personal injury, be sure to carry out disassembly/assembly
work within the specied range given in this Engineer's Manual and in the Instruction Manual.
2. Be sure to carry out replacement work after having installed the machine in a stable state in order to
protect against accident that can result in personal injury.
In addition, be sure to select appropriate tools.
3. In prevention of accident that can result in personal injury, make sure, after the completion of adjust-
ment work, that neither screws nor nuts are loosened or come in contact with other parts.
4. In prevention of accident that can result in personal injury, be sure to tighten screws and nuts in assem-
bly work with a specied torque, if specied, or with an appropriate torque, if not specied.
After the completion of assembly work, be sure to check that screws and nuts are not loosened before
starting test run.
5. In prevention of accident that can result in personal injury, be sure to check whether the direction of
rotation is correct at the time of test run.
6. In prevention of accident that can result in personal injury or entanglement accident, be sure to ensure
safety at the time of test run. In addition, be sure to take care not to allow hair or cloths to come in con-
tact with the machine belt.
PRECAUTIONS TO BE TAKEN IN VARIOUS OPERATION STAGES
Mechanical components
CAUTION

vi
Transportation
1. Be sure to lift this machine with four or more workers and use a carriage for moving it in order to pre-
vent personal injury.
2. Be sure to take sufcient safety measures to prevent falling or dropping before lifting or moving the
machine in order to protect against accident that can result in personal injury or death.
3. Installation is described in the Instruction Manual. Be sure to fully understand the description before
putting the machine into operation.
Replacement of parts
1. In prevention of accident caused by unfamiliarity with the machine or electrical-shock accident, be sure
to ask an electrical technician of your company or JUKI or distributor in your area for replacement of
electrical components.
2. When it is necessary to open the control box containing electrical parts, be sure to turn the power off
and wait for ve minutes or more before opening the cover in order to prevent accident caused by un-
familiarity with the machine or electrical-shock accident. In addition, do not carry out replacement work
with wet hands in order to prevent electrical-shock accident.
3. Be sure to replace parts according to the instructions given in this Engineer's Manual and in the Instruc-
tion Manual in order to protect against accident that can result in personal injury.
4. Be sure to carry out replacement work after having installed the machine in a stable state in order to
protect against accident that can result in personal injury.
In addition, be sure to select appropriate tools.
5. Make sure, after the completion of replacement work, that there is no loose soldering, no contact with
other parts, inadequate contact between connectors and receptacles, and loose screws/nuts in order to
protect against accident that can result in personal injury.
6. Make sure, after the completion of replacement work, that neither connectors nor cables are damaged,
slipped off or loosened in order to protect against accident that can result in personal injury.
It should be remembered that some parts have been factory-insulated with tubes or tapes, or oated
above the PWB for safety's sake. In addition, internal wiring has been factory-routed or -clamped in such
a way that it does not come close to high-voltage parts. Be sure to re-place those parts as they are at the
time of delivery.
7. Be sure to use JUKI genuine parts when replacing any of the machine parts.
JUKI assumes no responsibility for any accident caused by any part other than JUKI genuine one.
In addition, in the event you cannot replace parts within the specied range, immediately stop the re-
placement work and ask JUKI or distributor in your area for replacement of the parts.
8. If the fuse has blown, be sure to turn the power off and eliminate the cause of blowing of the fuse and
replace the blown fuse with a new one in order to prevent accident that can result in personal injury or
death.
Adjustment
1. In prevention of accident caused by unfamiliarity with the machine or electrical-shock accident, be sure
to ask an electrical technician of your company or JUKI or distributor in your area for adjustment of
electrical components.
2. When it is necessary to open the control box containing electrical parts, be sure to turn the power off
and wait for ve minutes or more before opening the cover in order to prevent accident caused by un-
familiarity with the machine or electrical-shock accident. In addition, do not carry out adjustment work
with wet hands in order to prevent electrical-shock accident.
3. In prevention of accident that can result in personal injury, adjust adjustment variable resistor or the like
installed on PWB within the specied range given in this Engineer's Manual and in the Instruction Manu-
al.
4. Be sure to carry out replacement work after having installed the machine in a stable state in order to
protect against accident that can result in personal injury.
In addition, be sure to select appropriate tools.
5. In prevention of accident that can result in personal injury, make sure, after the completion of adjust-
ment work, that neither screws nor nuts are loosened or come in contact with other parts.
6. Make sure, after the completion of replacement work, that neither connectors nor cables are damaged,
slipped off or loosened in order to protect against accident that can result in personal injury.
7. In prevention of accident that can result in personal injury or entanglement accident, be sure to ensure
safety at the time of test run. In addition, be sure to take care not to allow hair or cloths to come in con-
tact with the machine belt.
Disassembly/assembly
1. In prevention of accident that can result in personal injury, be sure to carry out disassembly/assembly
work within the specied range given in this Engineer's Manual and in the Instruction Manual.
PRECAUTIONS TO BE TAKEN IN VARIOUS OPERATION STAGES
Electrical components
CAUTION

vii
2. In prevention of accident caused by unfamiliarity with the machine or electrical-shock accident, be sure
to ask an electrical technician of your company or JUKI or distributor in your area for disassembly/as-
sembly of electrical components.
3. When it is necessary to open the control box containing electrical parts, be sure to turn the power off
and wait for ve minutes or more before opening the cover in order to prevent accident caused by unfa-
miliarity with the machine or electrical-shock accident. In addition, do not carry out disassembly/assem-
bly work with wet hands in order to prevent electrical-shock accident.
4. Be sure to carry out replacement work after having installed the machine in a stable state in order to
protect against accident that can result in personal injury.
In addition, be sure to select appropriate tools.
5. In prevention of accident that can result in personal injury, be sure to tighten screws and nuts in assem-
bly work with a specied torque, if specied, or with an appropriate torque, if not specied.
After the completion of assembly work, be sure to check that screws and nuts are not loosened before
starting test run.
6. In prevention of accident that can result in personal injury, make sure, after the completion of adjust-
ment work, that neither screws nor nuts are loosened or come in contact with other parts.
7. Make sure, after the completion of replacement work, that neither connectors nor cables are damaged,
slipped off or loosened in order to protect against accident that can result in personal injury.
It should be remembered that some parts have been factory-insulated with tubes or tapes, or oated
above the PWB for safety's sake. In addition, internal wiring has been factory-routed or -clamped in such
a way that it does not come close to high-voltage parts. Be sure to re-place those parts as they are at the
time of delivery.
8. In prevention of accident that can result in personal injury, be sure to check whether the direction of
rotation is correct at the time of test run.
9. In prevention of accident that can result in personal injury or entanglement accident, be sure to ensure
safety at the time of test run. In addition, be sure to take care not to allow hair or cloths to come in con-
tact with the machine belt.

viii
PRECAUTIONS TO BE TAKEN SO AS TO USE
THE MO-6800S SERIES MORE SAFELY
1. So as to avoid electric shock hazards, do not open the cover of the electrical box of
the motor or touch any part inside the electrical box with the power to the machine
turned ON.
1. To prevent possible personal injury, never operate the machine with the belt cover and
the eye guard removed.
2. To protect against possible personal injury resulting from being caught in the motor,
use a motor that is provided with a motor pulley cover.
3. To avoid electric shock hazards, never operate the machine with the ground wire for
the power supply removed.
4. During operation, be careful not to allow your or any other person’s head, hands or
ngers to come close to the handwheel, V belt and motor so as to prevent possible
personal injury that may occur when your hands/ngers are caught in the machine.
Also, do not place anything close to them.
5. So as to avoid possible injury to your hands and ngers, do not put any of them near
the cloth cutting knife and the needle when turning the power to the machine or while
the machine is in operation.
6. To prevent possible injury to your hands and ngers, do not put any of them inside
the eye guard while the machine is in operation.
7. To avoid electric shock hazards and accidents arising from damaged electrical com-
ponents, be sure to turn OFF the power switch before inserting/detaching the power
plug.
8. So as to protect against possible personal injury resulting from abrupt start of the ma-
chine, make sure to turn OFF the power to the machine when you leave your machine.
9. In the event of a power failure, be sure to turn OFF the power to the machine to protect
against possible personal injury resulting from abrupt start of the machine.
10. So as to protect against possible personal injury resulting from abrupt start of the
machine, remove the belt cover, motor pulley cover and the V belt after turning OFF
the power to the machine and conrming that the sewing machine will not run even by
depressing the start pedal.
11. Before inspecting, adjusting or cleaning the machine, threading the machine head or
replacing the needle, so as to protect against possible personal injury resulting from
abrupt start of the machine, be sure to turn OFF the power to the machine so as to
prevent an accident and conrm that the sewing machine will not operate even when
depressing the foot pedal of the sewing machine.
12. In order to protect against personal injury due to a fall of the sewing machine head,
never carry the sewing machine by holding the cloth plate cover. If you carry the sew-
ing machine by holding the cloth plate cover, the cover can break to allow the sewing
machine head to fall resulting in personal injury.
13. Be careful of handling this product so as not to pour water or oil, shock by dropping,
and the like since this product is a precision instrument.
14. Please operate this machine in 80% of the maximum speed in the rst four weeks for
engagement. After four weeks, please do not operate under the maximum speed until
replacing the new lubrication oil.
15. Periodically maintain and clean the machine to ensure and extend the usage term of
the machine.

ix
In addition, be aware that the safety devices such as the "eye protection cover" and "nger guard"
are sometimes omitted in the sketches, illustrations and gures included in the Engineer's Manual
for the explanation's sake. In the practical use, never remove those safety devices.
CAUTION
CAUTION BEFORE OPERATION
• Read and understand well the content of this instruction book.
• Know the functions of major parts and understand the notices.
• Truely realize the meanings of all warning tags.
• Realize and be familiar with how to operate this machine.
• Operators please to keep well mental status.
• Operators shall wear appropriate and proper working suits.
• Develop the familiarity of how to operate the machine if needed.
WARNING :
To avoid malfunction and damage of the machine, conrm the following.

x
CONTENTS
1. Specications........................................1
2.Names of major parts ...........................2
3.Model numbering system.....................3
4.Standard adjustment value ..................4
(1) Adjusting the needle height.................. 4
(2) Positioning the throat plate .................. 4
(3) Adjusting the lower looper ................... 6
1) Returning amount of the lower looper ....6
2) Clearance between the lower looper
and the needle ...........................................6
(4) Positioning the upper looper holder.... 8
(5) Positioning the upper looper.............. 10
1) The relationship between the needle
and the upper looper ..............................10
2) The relationship between the upper
looper and the lower looper ...................10
(6) Adjusting the double chain looper
(Applicable only to MO-6816S)........... 12
1) Returning amount of the double chain
looper .......................................................12
2) Longitudinal motion (Avoid motion) .....12
3) Clearance between the double chain
looper and the needle .............................12
(7) Adjusting the height and clearance
of the needle guard.............................. 14
1) For 1-needle or 2-needle overlock
machine....................................................14
2) For safely stitch machine .......................14
(8) Adjusting the height of the feed
dog ........................................................ 16
(9) Adjusting the tilt of the feed dog........ 16
(10) Adjusting the differential feed ratio ... 18
(11) Longitudinal position of the main
feed dog................................................ 18
(12) Adjusting the presser foot .................. 20
1) Adjusting the presser foot position ......20
2) Adjusting the lift amount of the
presser foot .............................................20
(13) Positioning the upper knife arm
shaft ...................................................... 22
(14) Replacing the upper and lower
knives and adjusting the overedging
width ..................................................... 24
1) Replace the upper knife..........................24
2) Replace the lower knife ..........................24
3) Adjusting the overedging width ............24
4) Resharpening of the knife ......................24
(15) Adjusting the thread cam equipment
(Applicable only to MO-6816S)........... 26
1) Adjusting the thread cam .......................26
2) Adjusting the thread cam thread
guides A and B and the thread cam
nail ............................................................26
3) Positioning the chain looper thread
guide.........................................................26
(16) Adjusting the looper cover ................. 28
(17) Adjusting the cloth chip cover ........... 28
(18) Adjusting the needle bar lubricating
pin ......................................................... 30
(19) Positioning the upper looper
lubricating pin...................................... 32
1) Orientation of the lubricating pin ..........32
2) Setting the lubricating pin......................32
(20) Positioning the thread take-up lever.. 34
1) Positioning the needle thread take-up
lever and the needle thread guide .........34
2) Positioning the looper thread take-up
lever and the looper thread guide .........34
(21) Lubrication and drainage.................... 36
1) Lubrication oil .........................................36
2) Drainage and rell the oil .......................36
5.Additional information and
precautions..........................................38
(1) Caution in assembly............................ 38
1) Application of sealant.............................38
2) Precautions to be taken with respect
to the lubricating components...............40
(2) Motor pulley and belt........................... 40
(3) Part number of frame support plate
bolt ........................................................ 41
(4) Inspection and replacement of the
oil lter.................................................. 41
(5) Cooling device ..................................... 41
6.Maintenance ........................................42
(1) Gauge table .......................................... 43
7.Adjusting the needle height and
looper timing .......................................44
8.Troubles and corrective measures....45
9.Drawing of table ..................................57
(1) Semi-sunken type................................ 57
(2) Fully-sunken type ................................ 58
(3) Auxiliary table for fully-sunken type.. 59

– 1 –
1. Specications
No. Model
Item
Specications
MO-6804S MO-6814S MO-6816S
1 Description 1-needle Overlock
machine
2-needle Overlock
machine
2-needle Safety stitch
machine
2 Stitch type F. S. T. JIS E13
(USA standard : 504)
JIS E24
(USA standard : 514)
JIS E13 + D12
(USA standard : 516)
3 Max. sewing speed 7,000 sti/min (Excluding some of subclass machines)
4 Stitch length 0.6 to 3.8 (4.5) mm / 60H : 1 to 4.5 mm
5 Needle gauge ―2.0 mm 3.0 mm, 5.0 mm
6 Overedging width 1.5 mm, 4.0 mm 2.0 mm, 3.0 mm, 4.0 mm 4.0 mm, 5.0 mm, 6.0 mm
7 Differential feed ratio Gathering 1 : 2 (Max. 1 : 4) / 60H ··· 1 : 1.7
Stretching 1 : 0.7 (Max. 1 : 0.6) / 60H ··· 1 : 0.9
8 Needle bar stroke 24.5 mm / 60H : 27.0 mm
9 Needle tilt angle 20°
10 Needle bar bushing Lower bushing type
11 Needle DC×27 (Standard) (Excluding some of subclass machines)
12 Presser lifting amount 5 to 7 mm
13 Presser foot pressure 44.1 N (4.5 kg) / 30P : 36.5 N (3.7 kg) / 60H : 54 N (5.5 kg)
14 Stitch adjusting method By pushbutton
15 Differential feed adjust-
ing method By lever (with micro adjustment mechanism)
16 Weight 27 kg
17 Lubrication Automatic lubrication type
18 Lubricating oil JUKI MACHINE OIL 18 (Equivalent to ISO VG 18)
19 Needle cooler Provided as standard
20 Needle thread heat
remover Provided as standard
21 Micro presser lifting
device Optional
22 Noise
-Equivalent continuous emission sound pressure level (LpA) at the worksta-
tion:
A-weighted value of 84.5 dB; (Includes KpA = 2.5 dB); according to ISO
10821- C.6.2 - ISO 11204 GR2 at 7,000 sti/min.
-Sound power level (LWA);
A-weighted value of 90.0 dB; (Includes KWA = 2.5 dB); according to ISO
10821- C.6.2 - ISO 3744 GR2 at 7,000 sti/min.

– 2 –
❶❺
❸
❹
❷
❻
2. Names of major parts
❶Presser foot lifting lever
❷Presser foot (asm.)
❸Thread stand
❹Oil gauge
❺Pulley
❻Cloth plate cover

– 3 –
3. Model numbering system
MO-6800S series model numbering system
1234567891011 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
M O 6 8 △ △ S◇□△△◇◇／□△△◇□△△△－□□△
3-6 Machine code
6804 1-needle 3-thread overlock
6814 2-needle 4-thread overlock
6816 2-needle 5-thread safety stitch
6843 3-needle 6-thread safety stitch
6845 2-needle double chainstitch
10 10 Feed dog code
4 2-row
6 3-row
* In the case that the machine code is "6845", it is
possible to use "6" only.
11 Material code
(Classication based on materials to be used)
1Extra light-weight to
lightweight materials
For light-weight materials such as
shirts or the like
2Light-weight to medi-
um-weight materials
Knit wear only
3 General fabrics
4
Medium-weight to
heavyweight materials
Knit wear only such as sweater or
the like
5Medium-weight to heavy-weight
materials such as denim or the like
6 Heavy-weight materials
9 Overedging width code
A 1.5 mm
D 3.0 mm
E 4.0 mm
F 5.0 mm
H 6.0 mm
* In the case that the machine code is "6845", it is
possible to use "F" only.
12 Application code (Classication based on type
of operation and process)
0 Standard
4 For attaching tape
5 For binding
6 For binding tape
13
Special machine code (Special classication
of machine, structure and specication other
than gauge set)
0 Special
H Standard
P Anti-material-slip capability type
15-22 Device and attachment code
G44/Q143 Presser foot (for sharp curve)/tape
guide for attaching tape
N075 Four-fold binder
8 Needle gauge code
0 1-needle
B 2.0 mm
D 3.0 mm
F 5.0 mm
1 5.0 + 2.0 mm
2 3.0 + 2.0 mm
* In the case that the machine code is "6845", it is
possible to use "F" only.
7Specication code
S Standard
24 Destination code
A Standard
B Europe
G China (Chinese domestic)
25 Accessory code
A Standard
B Europe
G China (Chinese domestic)
26 Table code
0 Fully-sunken
1 Semi-sunken

– 4 –
4. Standard adjustment value
(1) Adjusting the needle height
WARNING :
Turn OFF the power before starting the work so as to prevent accidents caused by abrupt start of the
sewing machine.
Standard adjustment
When the needle(s) is in the highest position, the needle height from the throat plate surface should be as
shown below.
A
04 14 16
ABCA
(Unit : mm)
Model A B C
1-needle overlock machine MO-6804S
10.4-10.6
2-needle overlock machine
MO-6814S-2 H(9.1)
MO-6814S-3 H
MO-6814S-4 H 11.8-12 (10.5)
MO-6814S-30P 10.4-10.6 (9.1)
Safety stitch machine
MO-6816S-3 H (7.6)
MO-6816S-50H 11.8-12 (9)
MO-6816S-60H 12.6-12.8 (9.8)
MO-6816S-30P 10.4-10.6 (7.6)
(2) Positioning the throat plate
WARNING :
Turn OFF the power before starting the work so as to prevent accidents caused by abrupt start of the
sewing machine.
Standard adjustment
The needle entry point should be such that the distanc-
es listed below are provided between the needle slot
edge of the throat plate and the center of needle.
(Unit : mm)
Standard 60H
A : Overlock side 1.2 1.8
B : Double chainstitch side 1.8 1.8
A
B
10°

– 5 –
Adjustment procedures Results of Improper adjustment
1. Take off the upper cover, loosen the clamping screw ❷of needle
driving forked crank ❶and move needle driving forked crank ❶
up or down to adjust the needle height.
❶
❷
(Caution) Do not fully loosen the clamping screw ❷of the
needle driving forked crank ❶. If the needle driving
forked crank has got out of position laterally when
its clamping screw was loosened, fully loosen the
clamping screw and turn pulley to allow the forked
crank to turn until it settles by itself. Then tighten the
clamping screw to x the forked crank at that posi-
tion.
o
Any other needle height than
specied here will badly affect
the action of the lower looper,
the timing for catching the upper
looper thread, etc.
o
Improper lateral position of the
needle driving forked crank ❶
will cause seizure, play, or other
troubles.
Adjustment procedures Results of Improper adjustment
1. Loosen four setscrews ❷of two throat plate bases ❶and move
two throat plate bases ❶back and forth to adjust dimension A or B.
❶
❷
❷
o
Improperly positioned throat
plate will cause needle break-
age, contact of the needles will
the throat plate, or other trou-
bles.

– 6 –
(3) Adjusting the lower looper
WARNING :
Turn OFF the power before starting the work so as to prevent accidents caused by abrupt start of the
sewing machine.
Standard adjustment
1) Returning amount of the lower looper
F: The distance between the blade point of the lower looper ❸and the center of the needle ❹should be
as follows when the lower looper ❸is at the extreme left of its stroke.
F
❶
❸❹
❷
F
❶
❸❹
❷
(Unit : mm)
Model F
1-needle overlock machine MO-6804S
3.7-3.9
2-needle overlock machine
MO-6814S-2 H
MO-6814S-3 H
MO-6814S-4 H 4.1-4.3
MO-6814S-30P 3.7-3.9
Safety stitch machine
MO-6816S-3 H
MO-6816S-50H 4.1-4.3
MO-6816S-60H
MO-6816S-30P 3.7-3.9
(Caution) The dimensions given in the table are
standard ones to be used to adjust the
looper. They are intended to be used for
reference and should be changed more
or less in accordance with the sewing
products and thread to be used.
2) Clearance between the lower looper and the needle
When the lower looper ❸moves to the right toward the center line of the needle ❹, the clearance be-
tween the blade point of the lower looper ❸and the scarf of the needle ❹should be 0.01 to 0.1 mm.
0.01 to 0.1mm
❸
❹
❸ ❸
❹ ❹
❶ ❶
❺❺
❷ ❷

– 7 –
Adjustment procedures Results of Improper adjustment
1) Returning amount of the lower looper
Loosen clamping screw ❷of lower looper support arm ❶and ad-
just lower looper ❸to make adjustment of the returning amount.
2) Clearance between the lower looper and the needle
1. Loosen clamping screw ❷of lower looper support arm ❶to the
extent that it is temporarily tightened.
2. Turn ne-adjustment screw ❺to adjust the clearance by moving
lower looper support arm ❶back and forth.
Turn ne-adjustment screw ❺clockwise to move lower looper ❸
away from the needle ❹. Turn it counterclockwise to move lower
looper ❸closer to the needle ❹.
o
Excessive returning amount of
the lower looper tends to cause
stitch skipping when lament
thread is used.
o
Insufcient returning amount of
the lower looper tends to cause
needle thread stitch skipping
when spun thread is used.
o
Excessive clearance will often
cause needle thread stitch skip-
ping.
o
Insufcient clearance will cause
needle breakage due to the con-
tact of the looper with the needle
❹, or produce scratches on the
blade point of the looper, leading
to needle thread breakage or
other troubles.

– 8 –
(4) Positioning the upper looper holder
WARNING :
Turn OFF the power before starting the work so as to prevent accidents caused by abrupt start of the
sewing machine.
Standard adjustment
H: The distance between the bottom surface Aof the frame and the upper end of the upper looper holder
pin ❷should be as shown below when the upper looper holder ❶is at the highest point of its stroke.
(Unit : mm)
Model H
1-needle overlock machine MO-6804S 48.4
2-needle overlock machine
MO-6814S-2 H 50.3
MO-6814S-3 H
MO-6814S-4 H 51.3
MO-6814S-30P 50.3
Safety stitch machine
MO-6816S-3 H 48.2
MO-6816S-50H 48.5
MO-6816S-60H 51.3
MO-6816S-30P 48.2
H
A
❶❺❹
❷
❻
0.1mm0.1mm
❸