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SERVICE INSTRUCTIONS FOR 
3M™ 12,000 RPM 5 in. (127 mm) 
and 6 in. (150 mm) 
RANDOM ORBITAL SANDERS 



3M™ Overhaul Service Kit 


The part number 20347, 3M™ Overhaul Service Kit, contains all the replacement parts that naturally 
wear over time and a straightforward manual to make servicing a 3M™ sander simple. Overhauling the 
Random Orbital Sander can be made even easier with the use of the above Service Tools. The Service 
Tools also reduce the chance of improper assembly. 


Part Number 

Description 

Qty 

3MA0040 

EXTERNAL RETAINING RING 

1 

3MA0021 

BEARING-2 SHIELDS 

1 

3MB0005 

ROTOR 

1 

3MA0010 

VANE 

5 

3MA0041 

WOODRUFF KEY 

1 

3MA0042 

O-RING 

1 

3MA0019 

BEARING -2 SHIELDS 

1 

3MA0938 

DOUBLE ROW ANGULAR CONTACT BEARING - 1 SEAL 

1 

3MA0039 

INTERNAL RETAINING RING 

1 

3MA0062 

INTERNAL MUFFLER 

1 

3MA0068 

MUFFLER INSERT 

1 

3MA0007 

VALVE 

1 

3MA0009 

VALVE SEAT 

1 

3MA0014 

VALVE SPRING 

1 

3MA0043 

O-RING 

1 

3MA0008 

VALVE STEM ASSEMBLY 

1 

3MA0166 

MUFFLER HOUSING 

1 

3MA0016 

SPACER 

1 

3MA1417 

INSTRUCTIONS FOR 5 in. AND 6 in. ROS OVERHAUL SERVICE KIT 

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12,000 RPM - 5 in. (127 mm) and 6 in. (150 mm) 
RANDOM ORBITAL SANDERS SERVICE INSTRUCTIONS 


NOTICE: To receive any expressed or implied warranty, the tool must be repaired by an authorized Service Center. 

The 5 in (127 mm.) and 6 in. (150 mm) Random Orbital Sander Service Instructions section provided is for use after completion of 
the warranty period. 


DISASSEMBLY INSTRUCTIONS 

Changing Grips: 

1. The Grip has two “tabs" that wrap around the body of 
the sander under the inlet and exhaust. Use a small 
screwdriver to pick out one of the “tabs" of the Grip, 
and then continue to go underneath the Grip with the 
screwdriver and pry the Grip off of sander. To install a 
new Grip, hold the Grip by the tabs making them face 
outward, align the Grip and slide it under the Throttle 
Lever then press the Grip down until it seats onto the 
top of the sander. Make sure the two “tabs" seat under 
the inlet and exhaust. 

Motor Disassembly: 

1. Lightly secure the tool in a vise using the T-7 Soft Collar 
or padded jaw vice and remove the pad with the 24 mm 
Pad Wrench then remove the Shroud or Skirt (which¬ 
ever applies). 

2. Remove the Lock Ring with the T-6 Motor Lock Ring 
Wrench/Spindle Puller Tool. The motor assembly can 
now be lifted out of the Housing. 

3. Secure the motor assembly by clamping the 5 in. or 6 
in. (125 or 150 mm) Shaft Balancer in a padded jaw vise 
and remove the Retaining Ring and the O-Ring from the 
Cylinder. 

4. Remove the Rear Endplate. This may require support¬ 
ing the Rear Endplate with a Bearing Separator and 
lightly pressing the shaft through the Bearing and Rear 
Endplate. Remove Cylinder and the Vanes and Rotor 
Set from the shaft of the Shaft Balancer. Remove the 
Key then press off the Front Endplate (with Bearing), O- 
Ring and the Lock Ring. It may be necessary to remove 
the Bearing with a Bearing Separator if it came out of 
the Front Endplate and stuck to the shaft of the Shaft 
Balancer. 

5. Remove the Bearing(s) from the Endplates by using the 
T-8 Bearing Removal Tool to press out the Bearings. 

Shaft Balancer and Spindle Disassembly: 

1. Grip the shaft end of the Shaft Balancer in a padded 
vise. With a thin screwdriver pick out the slotted end of 
the Retaining Ring and peel out. 

2. Screw the threaded end of the T-6 Motor Lock Ring 
Wrench/Spindle Puller Tool into the Spindle until hand 
tight. Apply a gentle heat from a propane torch or hot 
air gun to the large end of the Balancer Shaft until it is 
about 212° F (100° C) to soften the adhesive. Do not 
over heat. Remove the Spindle assembly by using the 
slider to give sharp outward blows to the Spindle. Allow 
the parts to cool so they are safe to handle. Follow one 
of the appropriate directions below: 

• If the Bearing come out with the spindle, use a small 
Bearing Separator to remove it. Move onto step 3. 

• If the Bearing stays in the Shaft Balancer. Follow 
steps A - D below. 


Procedure for removal of the Bearings from the Shaft 

Balancer: 

A. Position the Set Screw in the top of the T-9 12 mm ID 
Bearing Puller. 

B. Make sure the Retaining Ring is removed, then press 
the Bearing Puller into the I.D. of Bearing until the Bear¬ 
ing Puller hits the bottom of the Shaft Balancer. 

C. Thread the Set Screw down until it hits the bottom of the 
Shaft Balancer or becomes very tight. Grip the shaft end 
of the Shaft Balancer in a padded vise. 

D. Screw the threaded end of the T-6 Motor Lock Ring 
Wrench/Spindle Puller Tool into the Bearing Puller until 
hand tight. Apply a gentle heat from a propane torch 
or hot air gun to the large end of the Shaft Balancer to 
re-heat it until it is about 212° F (100° C) to soften the 
adhesive. Do not over heat. Remove the Bearing by 
using the slider to give sharp outward blows to the Bear¬ 
ing Puller. Allow the Bearing Puller, Bearing and Shaft 
Balancer to cool. After cooling, unthread the T-6 Motor 
Lock Ring Wrench/Spindle Puller Tool from the Bearing 
Puller. Back off the set screw. Secure the Bearing Puller 
and Bearings in a Bearing Separator and press out the 
Bearing Puller. 

3. The beraing shield components are held in place by the 
light press fit of the Retainer. These components can be 
damaged during removal and may need to be replaced 
if removed. To remove the Retainer, use an O-ring 
pick or a #8 sheet metal screw to grip and pull out the 
Retainer. Remove the Valve and Filter from the bore in 
the Shaft Balancer. If the Retainer and Valve were not 
damaged, they can be reused. However, the filter should 
be replaced on re-assembly. 

Housing Disassembly: 

1. For Non-Vacuum (NV) and Central Vacuum (CV) 
machines follow the steps outlined in Section I below. 

For Self Generated Vacuum (SGV) machines follow the 
steps outlined in Section III. 

I. This section is for NV and CV machines. 

A) Unscrew the Muffler Housing from the Housing. 

B) Remove the Bronze Muffler from the Muffler Housing 
and remove the Muffler insert from the cavity of the Muf¬ 
fler Housing. 

C) For NV machines move onto D. For CV machines move 
onto Section II. 

D) Remove the NV Shroud. Move onto Step 2. 

II. This section continued from Section I for CV Exhaust 
machines: 

A) Remove the Screw, Washer and Nut. 

B) Remove the 0 1 in. (28 mm) CV Swivel Exhaust As¬ 
sembly or the 0 3/4 in. (19 mm) CV Swivel Exhaust 
Assembly from the Shroud or Clean Sanding Shroud. 

C) Remove the Shroud or Clean Sanding Shroud from the 
Housing. Move onto step 2. 

III. This section is for SGV Exhaust machines: 

A) Unscrew the SGV Retainer with an 8 mm hex wrench. 


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B) Remove the 0 1 in. (28 mm) Hose SGV Swivel Exhaust 
Assembly from the Housing and SGV Skirt Adapter or 
SGV Shroud Adapter. 

C) Pull the SGV Retainer out of the bore of the Swivel 
Exhaust Assembly and remove the two O-rings. 

D) Remove the Vacuum Shroud or Vacuum Skirt from the 
Housing. Move onto step 2. 

2. Place the Speed Control to the midway position and 
remove the Retaining Ring. NOTE: If the machine is a 
vacuum model, the vacuum exhaust must be removed 
(see Section 1 above for removal) before the Retaining 
Ring can be removed with lock ring pliers. The Speed 
Control will now pull straight out. Remove the O-ring. 

3. Unscrew the Inlet Bushing Assembly from the Housing. 
Remove the Valve Spring, Valve, Valve Seat, Valve 
Stem and O-Ring. 

4. Press out the Spring Pin from the Housing and remove 
the Throttle Lever. 

ASSEMBLY INSTRUCTIONS 

NOTE: All assembly must be done with clean dry parts and 

all bearings are to be pressed in place by the correct tools 

and procedures as outlined by the bearing manufacturers. 

Housing Assembly: 

1. Install Throttle Lever into Housing with the Spring Pin. 

2. Lightly grease the O-ring and place it on the Speed 
Control. Install Valve Stem, O-ring (cleaned and lightly 
greased) and insert the Speed control into the Hous¬ 
ing in the midway position. Install the Retaining Ring. 
CAUTION: Make sure the Retaining Ring is completely 
snapped into groove in the Housing. 

3. Install the Valve Seat, the Valve and the Valve Spring. 
Coat the threads of the Bushing Assembly with 1 or 2 
drops of 3M Rite-Loc TL22 or equivalent non-permanent 
pipe thread sealant. Screw the assembly into the Hous¬ 
ing. Torque to 60 in/lbs (6.77 Nm.) 


4. For NV and CV machines follow the steps outlined in 
Section I below. For SGV machines follow the steps in 
Section III. 

I. This section is for CV and NV 

A) Place a clean felt Muffler all-the-way into the chamber of 
the Muffler Housing. Press the Bronze Muffler onto the 
Muffler Housing. 

B) Screw the Muffler Housing assembly into the Housing 
until hand tight. Use a 21 mm socket/torque wrench 
combination to torque the Muffler Housing. Torque to 20 
in/lbs (2.25 Nm). For NV machines move onto C. For CV 
machines move onto Section II. 

C) Install the Non-Vacuum Shroud onto the Housing by 
working the shroud over and around the bottom of the 
housing flanges. Make sure the line up slots (on the 
Housing) and tabs (on the Shroud) are engaged. Move 
onto the "Spindle, bearing shield and Shaft Balancer 
Assembly" Section. 

II. This section continued from Section I for CV Ex¬ 
haust machines: 

A) For 5 and 6 in. (125 and 150 mm) machines: 

(1) Install the 5 or 6 in. (125 or 150 mm. ) Shroud or 6 in. 
(150 mm) Clean Sanding Shroud onto the Housing by 
working the shroud over and around the bottom of the 
housing flanges. Slide the inlet end of the 0 1 in. (28 
mm) CV Swivel Exhaust Assembly or the 0 3/4 in. (19 
mm) CV Swivel Exhaust Assembly into the exhaust port 
of the Shroud or Clean Sanding Shroud until it hits the 
stop on the Swivel Exhaust Assembly. 

NOTE: For installation of Shrouds and Skirts make sure the 

line up slots (on the Housing) and tabs (on the Shroud or 

Skirt) are engaged. Make sure that the key on the Swivel 

Exhaust Assembly bracket is aligned and engaged with the 

keyway on the Housing. 

B) Place the Washer over the Screw. Thread the screw 



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into the mounting hole of the Swivel Exhaust Assembly 
and Housing until the end of the screw is flush with the 
inside surface of the Housing. Place the Nut into the 
cavity of the Housing and thread the Screw into the Nut 
until tight. Move onto the “Spindle, bearing shield and 
Shaft Balancer Assembly" Section. 

III. This section for SGV Exhaust machines: 

A) Install the Shroud or SGV Vacuum Skirt onto the Hous¬ 
ing by working the shroud or skirt over and around the 
bottom of the housing flanges. Make sure the line up 
slots (on the Housing) and tabs (on the Shroud or Skirt) 
are engaged. 

B) Attach the SGV Skirt Adapter or SGV Shroud Adapter to 
the exhaust port of the Shroud or SGV Skirt. 

C) Clean and lightly grease the two O-rings and place them 
in the two grooves in the SGV Retainer. 

D) Put the SGV Retainer into the mounting hole of the 0 1 
in. (28 mm) Hose SGV Swivel Exhaust Assembly. 

E) Push the 0 1 in. (28 mm) Hose SGV Swivel Exhaust 
Assembly into the exhaust port of the SGV Skirt Adapter 
or SGV Shroud Adapter. Screw the SGV Retainer into 
the threaded exhaust port on the Housing with an 8 mm 
Hex Wrench. Torque to 45 in/lbs (5.08 Nm. ). 

Spindle, Bearing Shield and Shaft Balancer Assembly: 

1. Place the Washer and Shim on the Spindle shaft with 

the curve of the Washer facing up so that the outside 
diameter of the washer will contact the outer diameter of 
the Bearing. Place the Bearing on the Spindle with the 
seal side toward the Washer. Press onto Spindle using 
the T-1B Spindle Bearing Press Tool (see figure) until 
seated at bottom. 

2. Insert Shim with tangs into the bottom of Spindle Bore 

of the Shaft Balancer. (Do not use this shim if Shaft 
Balancer text shows a + symbol.) 

3. When the Spindle Assembly is done correctly, the Bearing 

will rotate freely but not loosely. 

4. Take the new Filter and center it on the small bore that 
the original Filter was in before removal. With a small 
diameter screwdriver or flat-ended rod, press the Filter 
into the bore until it is flat in the bottom of the bore. 

Place the Valve into the bore so it is oriented correctly, 
then press the Retainer into the bore until it is flush with 
the bottom of the Bearing bore. 

5. Apply a pin head size drop of 3M Rite-Loc TL71 or 
equivalent to the outside diameter of each of the bear¬ 
ings on the spindle assembly. Spread the drop of bear¬ 
ing locker around the bearing until distributed evenly. 
CAUTION: Only a very small amount of bearing locker 
is needed to prevent rotation of the bearing OD. Any ex¬ 
cess will make future removal difficult. Place the Spindle 
Assembly into the bore of the Shaft Balancer and secure 
with the Retaining Ring. CAUTION: Make sure that the 
Retaining Ring is completely snapped into the groove in 
the Balancer Shaft. Allow the adhesive to cure. 

Motor Assembly: 

1. Use the larger end of the T-13 Bearing Press Sleeve to 
press the front Bearing (with 2 Shields) onto the shaft of 
the Shaft Balancer. 

2. Slide the Front Endplate with the bearing pocket facing 
down onto the Motor Shaft. Gently press the Front End- 


plate onto the Bearing using the larger end of the T-13 
Bearing Press Sleeve until the Front Bearing is seated 
in the bearing pocket of the Endplate. CAUTION: Only 
press just enough to seat the bearing into the pocket. 
Over-pressing can damage the bearing. 

3. Place the Key into the groove on the Shaft Balancer. 
Place the Rotor on the Shaft Balancer, making sure that 
it is a tight slip fit. 

4. Oil the five Vanes with a quality pneumatic tool oil and 
place them in the slots of the Rotor. Place the Cylinder 
Assembly over the Rotor with the short end of the 
Spring Pin engaging the blind hole in the Front End¬ 
plate. NOTE: The Spring Pin must project .060 in. (1.5 
mm) above the flanged side of the Cylinder. 

5. Press fit the rear Bearing (2 shields) into the Rear 
Endplate with the T-1 B Bearing Press Tool. Make sure 
the T-1B Press Tool is centered on the O.D. of the outer 
race. Lightly press fit the Rear Endplate and Bearing 
Assembly over the Shaft Balancer using the small end 
of the T-13 Bearing Press Sleeve. The sleeve should 
press only the inner race of the bearing. IMPORTANT: 
The Rear Endplate and Bearing Assembly is pressed 
correctly when the Cylinder is squeezed just enough 
between the Endplates to stop it from moving freely 
under its own weight when the shaft is held horizontal, 
but be able to slide between the Endplates with a very 
light force. If the assembly is pressed to tightly the 
motor will not run freely. If the pressed assembly is to 
loose, the motor will not turn freely after assembly in the 
Housing. Secure the assembly by placing the Retaining 
Ring in the groove of the Shaft Balancer. CAUTION: The 
Retaining Ring must be placed so that the middle and 
two ends of the hoop touch the Bearing first. Both raised 
center portions must be securely “snapped” into the 
groove in the Shaft Balancer by pushing on the curved 
portions with a small screwdriver. 

6. Lightly grease the O-Ring and place in the air inlet of the 
Cylinder Assembly. 

7. Lightly grease or oil the inside diameter of the Housing, 
line up the Spring Pin with the marking on the Housing 
and slide the Motor Assembly into the Housing. Make 
sure the Spring Pin engages the pocket in Housing. 

8. Carefully screw the Lock Ring into the Housing with the 
T-6 Motor Lock Ring Wrench/Spindle Puller Tool. Torque 
to 60 in/lbs (6.77 Nm.) NOTE: A simple technique 

to assure first thread engagement is to turn the lock 
ring counter clockwise with the T-6 Motor Lock Ring 
Wrench/Spindle Puller while applying light pressure. You 
will hear and feel a click when the lead thread of the lock 
ring drops into the lead thread of the housing. 

9. Spin on a new Pad and hand tighten it using a 24 mm 
Pad Wrench. 

Testing: 

Place 3 drops of quality pneumatic air tool oil directly into 
the motor inlet and connect it to a 90 psig (6.2 bar) air 
supply. A 12,000 RPM tool should run between 11,500 to 
12,000 RPM when the air pressure is 90 psig (6.2 bar) at 
the inlet of the tool while the tool is running at free speed. 
This free speed will be about 500 RPM to 1,000 RPM less 
when a Vacuum or Hook Face Pad is used because of wind 
resistance. This will not affect performance when sanding. 


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Troubleshooting Guide 


Symptom 

Possible Cause 

Solution 

Low Power and/or Low Free Speed 

Insufficient Air Pressure 

Check air line pressure at the Inlet of 
the Sander while the tool is running at 
free speed. It must be 90 psig (6.2 Bar). 

Clogged Muffler(s) 

See the “Housing Disassembly” section 
for Muffler removal. The Muffler can 
be back flushed with a clean, suitable 
cleaning solution until all contaminates 
and obstructions have been removed. If 
the Muffler can not be properly cleaned 
then replace it. Replace Muffler Insert 
(See the 

“Housing Assembly” Section). 

Plugged Inlet Screen 

Clean the Inlet Screen with a clean, 
suitable cleaning solution. If Screen 
does not come clean replace it. 

One or more Worn or Broken Vanes 

Install a complete set of new Vanes 
(all vanes must be replaced for proper 
operation). Coat all vanes with quality 
pneumatic tool oil. See “Motor Disas¬ 
sembly” and 
“Motor Assembly”. 

Internal air leakage in the Motor Housing 
indicated by higher than normal air con¬ 
sumption and lower than normal speed. 

Check for proper Motor alignment and 
Lock Ring engagement. Check for 
damaged O-Ring in Lock Ring groove. 
Remove Motor Assembly and Re-Install 
the Motor Assembly. See “Motor Disas¬ 
sembly" and “Motor Assembly”. 

Motor Parts Worn 

Overhaul Motor. Contact authorized 
Service Center. 

Worn or broken Spindle Bearings 

Replace the worn or broken Bearings. 
See “Shaft Balancer and Spindle Disas¬ 
sembly” and “Spindle Bearings, Bearing 
Shield and Shaft Balancer Assembly”. 

Air leakage through the Speed 
Control and/or Valve Stem. 

Dirty, broken or bent Valve Spring, Valve 
or Valve Seat. 

Disassemble, inspect and replace worn 
or damaged parts. See Steps 2 and 3 
in “Housing Disassembly” and Steps 2 
and 3 in “Housing Assembly”. 

Vibration/Rough Operation 

Incorrect Pad 

Only use Pad Sizes and Weights 
designed for the machine. 

Addition of interface pad or other material 

Only use abrasive and/or interface 
designed for the machine. Do not at¬ 
tach anything to the Sanders Pad face 
that was not specifically designed to be 
used with the Pad and Sander. 

Improper lubrication or buildup of foreign 
debris. 

Disassemble the Sander and clean in 
a suitable cleaning solution. Assemble 
the Sander. 

Worn or broken Rear or Front Motor 
Bearing(s) 

Replace the worn or broken Bearings. 
See “Motor Disassembly" and “Motor 
Assembly”. 

For vacuum machines it is possible to 
have too much vacuum while sanding on 
a flat surface causing the pad to stick to 
the sanding surface. 

For SGV machines add extra washer(s) 
to the pad spindle to increase the gap 
between the pad and shroud. For CV 
machines reduce vacuum through 
the vacuum system and/or add extra 
washer(s) to the pad. 


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Revision 10/03/07