Chicago Pneumatic CP3850 SERIES User manual

CP Technocenter 38, rue Bobby Sands -
BP10273 44800 Saint Herblain - France
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www.cp.com
CP3850 SERVICE
MANUAL

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Safety first!
Before starting, please read the following instructions.
Before repairing or adjusting any air tool, please read the following safety precautions and ensure that they are
understood. It is also necessary to make sure that the tool is disconnected from the air supply.
Hazards relating to Air Supply & Connections
Air under pressure may cause severe injury.
Always shut off air supply, drain hose or air pressure and disconnect tool from air supply when not in
use, before changing accessories or when making repairs.
Never point air in the direction of another person, even yourself.
Whipping hoses may cause severe injury. Always check for damaged or loose hoses and fittings.
Do not use quick disconnect couplings at tool. See instructions for correct setup.
Whenever universal twist couplings are us ed, lock pins must be installed.
Do not exceed the maximum air pressure marked on the tool or on the relevant service sheet. Under
no circumstances should a tool operate at more than 6.3bar/90psi.
Basic Safe Working Practices
Make sure that the workbench is clear and free from fluids, small parts, rags and cleaning materials
remaining from a previous task.
Excess hose dangling from the bench or lying on floor represents a potential tri p/slip/fall hazard.
Do not smoke anywhere near the workbench.
Beware of noise hazards. Using an air blow gun to clear small passages in components/assemblies
may cause high-frequency noise levels. In such a case, it is important to wear ear protectors and to
keep exposure time to a minimum.
Beware of dermatitis. When cleaning parts or handling oils and grease, protect your hands using
barrier cream or by wearing gloves.
When operating a tool, it is important wear impact resistant eye protection. Make sure that other
persons in the area also wear appropriate eye protection. Small components/accessories may fly off;
even grease or oil projected from a rotating shaft may cause severe irritation/inflammation of the eyes.
Keep clear of any rotating drive shafts.
Do not wear jewellery or loose clothing, especially exposed neckwear, which may result in choking. Do
not wear long garments near the tool when in use.
Avoid any direct contact with accessories, particularly when testing the tool after repair.

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CP3850 SERVICE
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General toolrepair information
Before embarking on a repair process, read all the relevant Chicago Pneumatic safety warning
sheetsand make sure that they are understood.
Only use genuine Chicago Pneumatic parts – see warranty conditions.
Read the relevant Chicago Pneumatic Service Sheet and make sure it is understood before
starting any repair.
Ensure that the alpha code on the service sheet matches the alpha code on the tool, otherwise the
parts may not be ordered correctly (alpha code = letter at the beginning of the serial number)
Rotor blades in grinder tools - some Chicago Pneumatic tools have rotor blades having a PTFE
content. Such tools can be identified by referring to the tool service sheet. It is important to observe
the warning printed in the service instructions concerning the handling of such material.
Ensure that the air supply equipment is correctly dimensioned in order to produce a volume that will
allow the tool to operate correctly.
Once repaired, replace all the warning and safety labels with new ones.
Lubricant :
Part number
Description
6159901480
Grease for bevel gear
Service sheet :
Part number
Description
2050553323 CP3850 SERIES

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CP3850 SERVICE
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Handle complete
(see p. 10)
Spring
Spring
Valve
Partition
Screw
Motor complete
(see p. 06)
Housing
Output shaft
complete
(see p. 08)
Ring
screw
Autobalancer
Front flange
Safety screw
Grinding wheel
Guard
Washer
Screw
Screw
Handle
bracket
Rotating
spacer
Washer
Screw
Rotating
exhaust
3.5 Nm
0.5 Nm
Loctite 222
45 Nm
Loctite 243
Exploded view of the tool
5 Nm

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CP3850 SERVICE
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Dismantling the tool
1. Remove the safety screw using the provided allen key and locking the output shaft with the stop finger
2. Unscrew the front flange using the provided pin spanner and locking the output shaft with the stop finger,
then remove the grinding wheel
3. Tighten the front flange of 2 turns on the shaft and remove the autobalanc er taking the tool in the hand
slam and taping with a mallet on the end of the shaft and on the front flange
4. Clamp horizontaly the head/housing of the tool in a vice. Ensure the stop finger is not clamped
5. Unscrew the 3 screws CHc M5x12 and remove the washers and the guard
6. Unscrew the ring screw (R/H thread)
7. Remove the tool from the vice
8. Using a mallet, tap on the housing to slide out the shaft unit
9. Turn vertically and clamp the housing of the tool in the vice. Ensure the stop finger is not clamped
10. Unscrew the 4 screws CHc M4x25 and remove the handle
11. Remove the spring cylindrical, the spring conical and slide out the partition
12. Remove the tool from the vice
13. Slide the motor unit out of the housing using a downwards movement and be carefull to get back the 4
pistons
Assembling the tool
1. Clamp horizontally the head/housing of the tool in a vice. Ensure the stop finger is not clamped
2. Slide the output shaft into the housing and fit it into the needle bearing taping carefully with a mallet. Check
the output for free rotation
3. Apply a drop of LOCTITE 243 on the first ring screw thread (R/H thread 45 Nm)
4. Place the guard onto the housing and tighten the 3 screws CHc M5x12 (R/H thread 5 Nm) with there
washer
5. Place the autobalancer on the output shaft
6. Place a new grinding wheel and screw on the front flange with the provided pin spanner
7. Tighten the safety screw with the provided Allen key
8. Remove the tool from the vice
9. Turn vertically and clamp the housing of the tool in the vice. Ensure the stop finger is not clamped
10. Apply the recommended quantity of grease réf. 6159901480 (19ml), onto the shaft bevel gear
11. Make the assembly of the 4 pistons onto the regulator housing and slide the motor unit back into the
housing. Take care to adjust the plate of the front end plat e with the one of the housing
12. Place and fit the partition into the housing
13. Place the spring cylindrical on the regulator housing
14. Place the valve on the partition and on the 4 piston‘s grooves, then the spring conical
15. Place and centre the handle on the housing, tighten the 4 screws CHc M4x25 (R/H thread 3.5 Nm)
16. Make sure of the good working of the safety lever before plugging on the tool air net work
17. Test the tool to make sure it works properly

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CP3850 SERVICE
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Motor unit
-
Rear end
plate
Blade
Front end
plate
O’ring
Pinion
Bearing
Spacer
Needle
Cylinder
Spigot
Rotor
Bearing
Regulator
LOCTITE 243
Piston
Regulator
housing
O’ring
Screw
O’ring
Spring
washer
Overspeed valve
+
Spring
Pin
Spirol
10 Nm
12 Nm
LOCTITE 243 →

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CP3850 SERVICE
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Dismantling the motor unit
1. Clamp vertically the housing of the tool in a vice. Ensure the stop finger is not clamped
2. Unscrew the 4 screws CHc M4x25 and remove the handle
3. Remove the spring cylindrical, the spring conical and slide out the partition
4. Remove the tool from the vice
5. Slide the motor unit out of the housing using a downwards movement and be carefull to get back th e 4
pistons
6. Remove the o’ring and the 2 pin Spirol that retain the regulator housing with a pliers
7. Remove the regulator housing and clamp the motor unit in a vice on the drive gear plates
8. Unscrew the regulator (L/H thread) from the motor unit (see Fig.1)
9. Using an extractor, remove the complete rear end plate
10. Extract the bearing, the spring washer and the o’ring of the rear end plate
11. Remove the cylinder and the 4 blades
12. Turn the motor unit over and hold the rotor in a vice with protection
13. Unscrew the pinion (R/H thread)
14. Remove the front end plate with the bearing and the O-ring
15. Remove the spacer from the spigot
Reassembling the motor unit
1. Clamp the rotor in a vic e with protection
2. Fit the spacer over the spigot of the rotor. Be carefull to put the chamfer on the rotor side (see Fig.2)
3. Fit a new O-ring into the groove of the front end plate and place it over the spigot of the rotor
4. Position a new bearing onto the tip of the rotor and press it to position first on the outer race of the bearing
and then on the inner race
5. Apply a drop of LOCTITE 243 on the first thread of the pinion and tighten it on the rotor (R/H thread 10 Nm)
6. Turn the motor unit over held by the drive gear in the vice
7. Fit 4 new blades into the rotor slots
8. Place the cylinder on the rotor (ensure correct orientation of the cylinder plate on plate with the pin hole on
the top)
9. Position the rear end plate onto the cylinder (ensure correct orientation and that the pin is placed in the
hole inside the cylinder)
10. Place the spring was her and a new o’ring inside his groove
11. Position a new bearing on the rotor and press it into position
12. Check the motor unit for free rotation
13. Apply a drop of LOCTITE 243 onto the female thread at the end of the rotor
14. Screw the governor onto the motor unit (L/H thread at 1.5 Nm)
15. Place the regulator housing on the rear end plate, fit the 2 pin Spirol with a hammer and screw the
regulator housing (R/H 12 Nm)
16. Place the 4 pistons into the regulator housing and a new o’ring in his groove
17. Remove the motor unit from the vice
18. Clamp vertically the housing of the tool in a vice. Ensure the stop finger is not clamped
19. Slide the motor unit back into the housing. Take care to adjust the plate of the front end plate with the one
of the housing
20. Place and fit the partition into the housing
21. Place the spring cylindrical on the regulator housing
22. Place the valve on the partition and on the 4 piston‘s grooves, then the spring conical
23. Place and centre the handle on the housing, tighten the 4 screws CHc M4x25 (R/H thread 3.5 Nm)
24. Make sure of the good working of the safety lever before plugging on the tool air network
25. Test the tool to make sure it works properly
Fig. 1
Fig. 2

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CP3850 SERVICE
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Shaft unit
Dismantling the shaft unit
1. Remove the safety screw using the provided allen key and
locking the output shaft with the stop finger
2. Unscrew the front flange using the provided pin spanner and
locking the output shaft with the stop finger, then remove the
grinding wheel
3. Tighten the front flange of 2 turns on the shaft and remove t he
autobalancer taking the tool in t he hand slam and taping with a
mallet on the end of the shaft and on the front flange
4. Clamp the head/housing of the tool in a vice. Ensure the stop
finger is not clamped
5. Unscrew the 3 screws CHc M5x12 and remove the washers and
the guard
6. Unscrew the ring screw (R/H thread)
7. Remove the tool from the vice
8. Using a mallet, tap on the housing to slide out the shaft unit
9. Unscrew the nut (R/ H thread)
10. Using an extractor, remove the bevel gear and the deflector
11. Using an extractor, remove the bearing
Reassembling the shaft unit
1. Position the new bearing ont o the spindle and press it into
position
2. Press the parallel key
3. Place the deflector onto the new bevel gear
4. Position the bevel gear onto the output shaft
5. Apply a drop of LOCTITE 243 on the first thread of the shaft and
tighten the nut (R/H thread 25 Nm)
6. Apply the recommended quantity of grease, réf. 6159901480 (19
ml), onto the shaft bevel gear
7. Clamp horizontally the head/housing of the tool in a vice. Ensure
the stop finger is not clamped
8. Slide the output shaft into the housing and fit it into the needle
bearing taping carefully with a mallet. Check the output for free
rotation
9. Apply a drop of LOCTITE 243 on the first ring screw thread (R/H
thread 45 Nm)
10. Place the guard onto the housing and tighten the 3 screws CHc
M5x12 (R/H thread 5 Nm) with there washer
11. Place the autobalancer on the output shaft
12. Place a new grinding wheel and screw on the front flange with
the provided pin spanner
13. Tighten the safety screw with the provided Allen key
14. Test the tool to make sure it works properly
Bearing
Nut
Bevel gear
Déflector
Output spindle
Parallel key
25 Nm
LOCTITE 243

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CP3850 SERVICE
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CP3850 SERVICE
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Handle complete
Handle
Bushing
inlet
O’ring
Screen
Spring
conical
Ball
Ball chair
Spring
cylindrical
Needle
Lever
Latch lever
Spring
Grooved
pin
Ball
Inlet
bushing
60 Nm

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CP3850 SERVICE
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Dismantling of the handle
1. Clamp vertically the housing of the tool in a vice. Ensure the stop finger is not clamped
2. Unscrew the 4 screws CHc M4x25 and remove the handle
3. Remove the inlet bushing
4. Clamp the handle in a vice with protection
5. Unscrew the bushing inlet and remove the o’ring
6. Remove the screen, the spring conical, the ball and the ball chair
7. Remove the handle from the vice
8. Slide out the needle and take the spring cylindrical
9. Clamp the handle in a vice with protection
10. With a drift punch, remove the grooved pin that holds the latch lever and the latch lever springl
11. With a drift punch, remove the grooved pin that holds the lever
Reassembling of the handle
1. Clamp the handle in a vice with protection
2. Place the latch lever and his spring into the handle, t hen fit the smallest of the 2 grooved pin with a
hammer and a drift punch
3. Place the lever into the handle, then fit the longgest of the 2 grooved pin with a hammer and a drift punch
4. Remove the handle from the vice
5. Slide the needle by the back of the handle until it comes in contact with the lever, fit the spring on the lever
6. Clamp the handle in a vice with protection
7. Fit the ball chair into the handle
8. Fit the ball, the spring conical and the screen
9. Place a new o’ring on the bushing inlet and tighten it (R/H thread 60 Nm)
10. Remove the handle from the vice
11. Fit the inlet bushing
12. Clamp vertically the housing of the tool in a vice. Ensure the stop finger is not clamped
13. Place and centre the handle on the housing, tighten the 4 screws CHc M4x25 (R/H thread 3.5 Nm)
14. Make sure of the good working of the safety lever before plugging on the tool air network
15. Test the tool to make sure it works properly

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CP3850 SERVICE
MANUAL
Tool performance
Performance data, based on a 6.3 bars dynamic line pressure at the hos e inlet.
Any reduction in air pressure may result in a loss of performance.
Declared speed :
8500 rpm
8500 rpm
8500 rpm
7700 rpm
6500 rpm
6500 rpm
6000 rpm
Copyright 2015, Chicago Pneumatic Tool Co. LLC
All rights reserved. Any unauthorised use or copy of the contents herein, whether in part or in full, is prohibited.
This particularly applies to trademarks, brand names, part numbers and drawings.
Only genuine parts used. Warranty or Product Liability does not cover any damages or malfunction due to the use
of unauthorised parts.
CP3850-85AB7V
CP3850-85AH7VE
CP3850-85AB7VE
CP3850-77AB7V
CP3850-65AB9VE
CP3850-65AH9VE
CP3850-60AB9V