Instruction Manual
Page 2
... Chain Drive, Chain Brake, Chain Tensioner 9 3.3 Chain Lubrication 11 3.4 Rewind Starter 12 3.5 Ignition System 14 3.6 Carburetor 15 3.7 Engine 18 4. Engine 32 6.1 6.2 6.2.1 6.2.2 6.2.3 6.3 6.3.1 6.3.2 6.4 6.5 6.6 6.7 6.8 6.9 Muffler 32 Leakage Test 33 Preparations 33 Vacuum Test ...Machines with Manual Fuel Pump 85 12.5 Carburetor 88 12.5.1 Leakage Test 89 RA_737_00_01_01 MS 231, MS 231 C, MS 251, MS 251 C q © ANDREAS STIHL AG & Co. Specifications 5 2.1 Engine 5 2.2 Fuel System 5 2.3 Ignition System 5 2.4 Chain Lubrication 5 2.5 Tightening ...
... Chain Drive, Chain Brake, Chain Tensioner 9 3.3 Chain Lubrication 11 3.4 Rewind Starter 12 3.5 Ignition System 14 3.6 Carburetor 15 3.7 Engine 18 4. Engine 32 6.1 6.2 6.2.1 6.2.2 6.2.3 6.3 6.3.1 6.3.2 6.4 6.5 6.6 6.7 6.8 6.9 Muffler 32 Leakage Test 33 Preparations 33 Vacuum Test ...Machines with Manual Fuel Pump 85 12.5 Carburetor 88 12.5.1 Leakage Test 89 RA_737_00_01_01 MS 231, MS 231 C, MS 251, MS 251 C q © ANDREAS STIHL AG & Co. Specifications 5 2.1 Engine 5 2.2 Fuel System 5 2.3 Ignition System 5 2.4 Chain Lubrication 5 2.5 Tightening ...
Instruction Manual
Page 4
... on the machine, may have been introduced since they, depending on the engine housing. The meanings are intended exclusively for all special servicing tools currently available from STIHL. They must not project since publication of properly equipped repair shops. MS 231, MS 231 C, MS 251, MS 251 C 3 To help locate the fault, consult the chapter on "Special Servicing...
... on the machine, may have been introduced since they, depending on the engine housing. The meanings are intended exclusively for all special servicing tools currently available from STIHL. They must not project since publication of properly equipped repair shops. MS 231, MS 231 C, MS 251, MS 251 C 3 To help locate the fault, consult the chapter on "Special Servicing...
Instruction Manual
Page 5
... local and countryspecific safety regulations as well as necessary. They can be identified by hand, to ensure the tightness of STIHL press fluid, b 14. Preparations for wear or damage before carrying out repairs or mounting the machine to the assembly stand...engine damage due to a specific torque or coated with local environmental regulations. 1.2 Safety Precautions If the machine is otherwise a risk of injury from the fanwheel and a risk of heat near the fuel. All work , observe all machine components that have to be tightened to overheating. 4 MS 231, MS 231 C, MS 251, MS 251...
... local and countryspecific safety regulations as well as necessary. They can be identified by hand, to ensure the tightness of STIHL press fluid, b 14. Preparations for wear or damage before carrying out repairs or mounting the machine to the assembly stand...engine damage due to a specific torque or coated with local environmental regulations. 1.2 Safety Precautions If the machine is otherwise a risk of injury from the fanwheel and a risk of heat near the fuel. All work , observe all machine components that have to be tightened to overheating. 4 MS 231, MS 231 C, MS 251, MS 251...
Instruction Manual
Page 6
... engine speed with bar and chain: Idle speed: Clutch: Clutch engages at: Crankcase leakage test at gauge pressure: under vacuum: 2.2 Fuel System 2.3 Ignition System 2.4 Chain Lubrication MS 231 40.6 cm3 41.5 mm 30.0 mm 2.0 kW (2.7 bhp) at 9,500 rpm 13,000 rpm 2,800 rpm Centrifugal clutch without linings 3,500 rpm 0.5 bar 0.5 bar MS 251... (resistor type): Electrode gap: 0.30 (+ 0.05/- 0.10) mm NGK CMR 6 H 0.5 mm Speed-controlled Ematic oil pump Oil delivery rate: 8.0 (+/3.0) cm3/min at 10,000 rpm MS 231, MS 231 C, MS 251, MS 251 C 5 2.
... engine speed with bar and chain: Idle speed: Clutch: Clutch engages at: Crankcase leakage test at gauge pressure: under vacuum: 2.2 Fuel System 2.3 Ignition System 2.4 Chain Lubrication MS 231 40.6 cm3 41.5 mm 30.0 mm 2.0 kW (2.7 bhp) at 9,500 rpm 13,000 rpm 2,800 rpm Centrifugal clutch without linings 3,500 rpm 0.5 bar 0.5 bar MS 251... (resistor type): Electrode gap: 0.30 (+ 0.05/- 0.10) mm NGK CMR 6 H 0.5 mm Speed-controlled Ematic oil pump Oil delivery rate: 8.0 (+/3.0) cm3/min at 10,000 rpm MS 231, MS 231 C, MS 251, MS 251 C 5 2.
Instruction Manual
Page 7
... first time. 2.5 Tightening Torques DG and P (Plastoform) screws are installed for bar / engine housing 16.0 (repair solution) P 5x18 Cover, chain brake / engine housing 4.0 M 5 Filter base / baffle / carburetor 3.5 P 6x26.5 Handlebar / tank ... / engine housing 4.0 P 4x12 Air baffle / engine housing 2.0 M 12x1 L Carrier / crankshaft 50.0 P 6x28 Engine housing / bearing plug 6.0 D 4x16 Oil pump 4.0 M 5x16 Muffler / cylinder 10.0 M 8x1 Flywheel / crankshaft 28.0 P 4x10 Retainer 1.0 Q B 2), 3) 2) 1), 3) 1), 3) 1), 3) 2), 3) 4) 6 MS 231, MS 231 C, MS 251, MS 251 C...
... first time. 2.5 Tightening Torques DG and P (Plastoform) screws are installed for bar / engine housing 16.0 (repair solution) P 5x18 Cover, chain brake / engine housing 4.0 M 5 Filter base / baffle / carburetor 3.5 P 6x26.5 Handlebar / tank ... / engine housing 4.0 P 4x12 Air baffle / engine housing 2.0 M 12x1 L Carrier / crankshaft 50.0 P 6x28 Engine housing / bearing plug 6.0 D 4x16 Oil pump 4.0 M 5x16 Muffler / cylinder 10.0 M 8x1 Flywheel / crankshaft 28.0 P 4x10 Retainer 1.0 Q B 2), 3) 2) 1), 3) 1), 3) 1), 3) 2), 3) 4) 6 MS 231, MS 231 C, MS 251, MS 251 C...
Instruction Manual
Page 8
.... Fastener Thread size For component Torque Nm Remarks Screw Screw Screw Screw P 4x12 P 4x10 M 10x1 D 4x20 D 5.3x41 Pre-separator / engine housing Elbow connector / air guide shroud Spark plug / cylinder Ignition module/cylinder Cylinder / engine housing 2.0 1.6 12.0 4.5 11.0 1), 3) Remarks: 1) Screws with binding head 2) Micro-encapsulated screws 3) Waxed screws 4) Degrease crankshaft/flywheel and mount... refitting a DG or P screw in an existing thread: Place the screw in the existing thread and does not form a new thread and weaken the assembly. MS 231, MS 231 C, MS 251, MS 251 C 7
.... Fastener Thread size For component Torque Nm Remarks Screw Screw Screw Screw P 4x12 P 4x10 M 10x1 D 4x20 D 5.3x41 Pre-separator / engine housing Elbow connector / air guide shroud Spark plug / cylinder Ignition module/cylinder Cylinder / engine housing 2.0 1.6 12.0 4.5 11.0 1), 3) Remarks: 1) Screws with binding head 2) Micro-encapsulated screws 3) Waxed screws 4) Degrease crankshaft/flywheel and mount... refitting a DG or P screw in an existing thread: Place the screw in the existing thread and does not form a new thread and weaken the assembly. MS 231, MS 231 C, MS 251, MS 251 C 7
Instruction Manual
Page 9
... full load Cause Clutch shoes badly worn Clutch drum badly worn Remedy Install new clutch Install new clutch drum Saw chain rotates at idle speed Engine idle speed too high Clutch springs stretched Clutch springs broken Readjust idle speed screw LA Replace the clutch springs or install new clutch Replace the... Clutch shoe retainer broken Clutch shoes and carrier worn Replace all clutch springs Fit new needle cage Install new retainer or clutch Install new clutch 8 MS 231, MS 231 C, MS 251, MS 251 C 3.
... full load Cause Clutch shoes badly worn Clutch drum badly worn Remedy Install new clutch Install new clutch drum Saw chain rotates at idle speed Engine idle speed too high Clutch springs stretched Clutch springs broken Readjust idle speed screw LA Replace the clutch springs or install new clutch Replace the... Clutch shoe retainer broken Clutch shoes and carrier worn Replace all clutch springs Fit new needle cage Install new retainer or clutch Install new clutch 8 MS 231, MS 231 C, MS 251, MS 251 C 3.
Instruction Manual
Page 10
... Brake band blocked Install new clutch Install new clutch drum Check freedom of movement and operation of brake band Saw chain rotates at idle speed Engine idle speed too high Clutch springs stretched Clutch springs broken Readjust idle speed screw LA Replace the clutch springs or install new clutch Replace the... Brake spring stretched or broken Fit new brake spring Brake band stretched or worn Clutch drum worn Fit new brake band Install new clutch drum MS 231, MS 231 C, MS 251, MS 251 C 9
... Brake band blocked Install new clutch Install new clutch drum Check freedom of movement and operation of brake band Saw chain rotates at idle speed Engine idle speed too high Clutch springs stretched Clutch springs broken Readjust idle speed screw LA Replace the clutch springs or install new clutch Replace the... Brake spring stretched or broken Fit new brake spring Brake band stretched or worn Clutch drum worn Fit new brake band Install new clutch drum MS 231, MS 231 C, MS 251, MS 251 C 9
Instruction Manual
Page 12
... cracked Install new oil pump Install new oil intake hose Install new engine housing Oil pump delivers insufficient oil Oil pump damaged or worn Worm driver is loose Install new oil pump Install new worm MS 231, MS 231 C, MS 251, MS 251 C 11 rectify other sources of trouble with the chain lubrication system, check and . 3.3 Chain...
... cracked Install new oil pump Install new oil intake hose Install new engine housing Oil pump delivers insufficient oil Oil pump damaged or worn Worm driver is loose Install new oil pump Install new worm MS 231, MS 231 C, MS 251, MS 251 C 11 rectify other sources of trouble with the chain lubrication system, check and . 3.3 Chain...
Instruction Manual
Page 15
... break in flywheel Install new flywheel Irregular spark Check operation of adjustment - 3.5 Ignition System Condition Engine runs roughly, misfires, temporary loss of the spark plug, clean or replace spark plug if necessary. 14 MS 231, MS 231 C, MS 251, MS 251 C Check operation of power Cause Remedy Spark plug boot is loose Press boot firmly onto spark...
... break in flywheel Install new flywheel Irregular spark Check operation of adjustment - 3.5 Ignition System Condition Engine runs roughly, misfires, temporary loss of the spark plug, clean or replace spark plug if necessary. 14 MS 231, MS 231 C, MS 251, MS 251 C Check operation of power Cause Remedy Spark plug boot is loose Press boot firmly onto spark...
Instruction Manual
Page 16
... Fit a new metering diaphragm Tank vent faulty Replace tank vent Leak on fuel hose from tank to carburetor Seal connections or install new fuel hose Engine loses power during acceleration Sealing ring or spring in valve seat or cone Remove and clean the inlet needle, clean the carburetor Inlet needle worn... control lever sticking on spindle Check the inlet control lever and replace if necessary. foreign matter in accelerator Install new carburetor pump worn or damaged MS 231, MS 231 C, MS 251, MS 251 C 15 engine stalls Cause Remedy Inlet needle not sealing -
... Fit a new metering diaphragm Tank vent faulty Replace tank vent Leak on fuel hose from tank to carburetor Seal connections or install new fuel hose Engine loses power during acceleration Sealing ring or spring in valve seat or cone Remove and clean the inlet needle, clean the carburetor Inlet needle worn... control lever sticking on spindle Check the inlet control lever and replace if necessary. foreign matter in accelerator Install new carburetor pump worn or damaged MS 231, MS 231 C, MS 251, MS 251 C 15 engine stalls Cause Remedy Inlet needle not sealing -
Instruction Manual
Page 17
...Reset idle speed screw (LA) high idle speed screw (LA) correctly Oil seals/engine pan leaking Seal or replace oil seals/engine pan Throttle shutter does not close Install new carburetor Engine stops while idling Idle jet bores or ports blocked Low speed screw too rich ...to carburetor Seal connections or install new fuel hose Engine idle speed too high Readjust with idle speed screw LA (counterclockwise) Clutch springs stretched or fatigued Replace the clutch springs or install new clutch Clutch spring hooks broken Replace the clutch springs 16 MS 231, MS 231 C, MS 251, MS 251 C
...Reset idle speed screw (LA) high idle speed screw (LA) correctly Oil seals/engine pan leaking Seal or replace oil seals/engine pan Throttle shutter does not close Install new carburetor Engine stops while idling Idle jet bores or ports blocked Low speed screw too rich ...to carburetor Seal connections or install new fuel hose Engine idle speed too high Readjust with idle speed screw LA (counterclockwise) Clutch springs stretched or fatigued Replace the clutch springs or install new clutch Clutch spring hooks broken Replace the clutch springs 16 MS 231, MS 231 C, MS 251, MS 251 C
Instruction Manual
Page 18
Condition Cause Engine speed drops quickly under Air filter dirty load - low power Remedy Clean air filter or replace if necessary Throttle shutter not opened fully Tank vent ... Clean fuel strainer in flywheel has sheared off Install new flywheel Engine running extremely rich, has Choke shutter does not open no power and a very low maximum speed Check carburetor and choke shaft, service or replace if necessary MS 231, MS 231 C, MS 251, MS 251 C 17 key in carburetor, replace if necessary Leak on fuel hose...
Condition Cause Engine speed drops quickly under Air filter dirty load - low power Remedy Clean air filter or replace if necessary Throttle shutter not opened fully Tank vent ... Clean fuel strainer in flywheel has sheared off Install new flywheel Engine running extremely rich, has Choke shutter does not open no power and a very low maximum speed Check carburetor and choke shaft, service or replace if necessary MS 231, MS 231 C, MS 251, MS 251 C 17 key in carburetor, replace if necessary Leak on fuel hose...
Instruction Manual
Page 19
... kinks Clean bore or install new manifold. Air filter - Fuel system - 3.7 Engine Always check and, if necessary, repair the following parts before looking for faults on fan housing 18 MS 231, MS 231 C, MS 251, MS 251 C Clean bore or install new manifold. Carburetor - Air inlets in fan housing ...blocked or cooling fins on cylinder very dirty Thoroughly clean all cooling air openings and the cylinder fins Air inlet in engine damaged at idle speed,...
... kinks Clean bore or install new manifold. Air filter - Fuel system - 3.7 Engine Always check and, if necessary, repair the following parts before looking for faults on fan housing 18 MS 231, MS 231 C, MS 251, MS 251 C Clean bore or install new manifold. Carburetor - Air inlets in fan housing ...blocked or cooling fins on cylinder very dirty Thoroughly clean all cooling air openings and the cylinder fins Air inlet in engine damaged at idle speed,...
Instruction Manual
Page 21
Contamination (with QuickStop Super - Remove the clutch drum, b 4.1 - Starting the engine 2 1 - Disengage the chain brake 2 OP 1 : Turn the brake band (1) to troubleshooting, b 3.2. If the chain brake does not operate properly, refer to one of the most ... inside diameter and/or parts of the chain braking time, i.e. 5. The clutch drum must not rotate. : Pry the brake band (2) out of the machine. 20 MS 231, MS 231 C, MS 251, MS 251 C
Contamination (with QuickStop Super - Remove the clutch drum, b 4.1 - Starting the engine 2 1 - Disengage the chain brake 2 OP 1 : Turn the brake band (1) to troubleshooting, b 3.2. If the chain brake does not operate properly, refer to one of the most ... inside diameter and/or parts of the chain braking time, i.e. 5. The clutch drum must not rotate. : Pry the brake band (2) out of the machine. 20 MS 231, MS 231 C, MS 251, MS 251 C
Instruction Manual
Page 23
...if necessary. 3 2 : Fit the strap (1) on the pivot pins (2) and (3) so that the brake spring attachment point (arrow) is worn, install a new engine housing. - Remove the hand guard and brake lever. - Lubricate the pivot pins, b 14 1 2 1 : Slip the spacer washer (1) onto the pin (2). 1... as stop. : Hold the brake lever (2) so that "TOP" faces outwards and the curve (arrow) faces up the holes. 2310RA023 TG 22 MS 231, MS 231 C, MS 251, MS 251 C Clean the pivot pins and disassembled parts, b 14 - 1 2 1 1 TOP 2310RA021 TG 2310RA019 TG 2310RA016 TG : Remove the retaining ring...
...if necessary. 3 2 : Fit the strap (1) on the pivot pins (2) and (3) so that the brake spring attachment point (arrow) is worn, install a new engine housing. - Remove the hand guard and brake lever. - Lubricate the pivot pins, b 14 1 2 1 : Slip the spacer washer (1) onto the pin (2). 1... as stop. : Hold the brake lever (2) so that "TOP" faces outwards and the curve (arrow) faces up the holes. 2310RA023 TG 22 MS 231, MS 231 C, MS 251, MS 251 C Clean the pivot pins and disassembled parts, b 14 - 1 2 1 1 TOP 2310RA021 TG 2310RA019 TG 2310RA016 TG : Remove the retaining ring...
Instruction Manual
Page 24
... spring's anchor pin is not the case, replace the brake spring. - MS 231, MS 231 C, MS 251, MS 251 C 23 - If the groove in the reverse sequence. 2310RA026 TG : Push the flat spring (1) slightly to the anchor pin (arrow). - If this is worn, install a new engine housing, b 6.6 2310RA028 TG : Use the assembly tool (2) 1117 890 0900 to...
... spring's anchor pin is not the case, replace the brake spring. - MS 231, MS 231 C, MS 251, MS 251 C 23 - If the groove in the reverse sequence. 2310RA026 TG : Push the flat spring (1) slightly to the anchor pin (arrow). - If this is worn, install a new engine housing, b 6.6 2310RA028 TG : Use the assembly tool (2) 1117 890 0900 to...
Instruction Manual
Page 25
... housing, b 8.2 - Check the cam on Machines with QuickStop Super 2 2 - Remove the brake spring from the anchor pin (arrow). - The brake spring is worn, install a new engine housing. - Troubleshooting, b 3.2 - Check the anchor pin - if it is now relaxed. : Use the assembly tool 1117 890 0900 to disconnect the brake spring (1) from the... and brake lever. 2310RA033 TG 1 : Take the brake lever (2) out of the flat spring (1) into its seat (arrow) as far as stop. 2310RA020 TG 24 MS 231, MS 231 C, MS 251, MS 251 C
... housing, b 8.2 - Check the cam on Machines with QuickStop Super 2 2 - Remove the brake spring from the anchor pin (arrow). - The brake spring is worn, install a new engine housing. - Troubleshooting, b 3.2 - Check the anchor pin - if it is now relaxed. : Use the assembly tool 1117 890 0900 to disconnect the brake spring (1) from the... and brake lever. 2310RA033 TG 1 : Take the brake lever (2) out of the flat spring (1) into its seat (arrow) as far as stop. 2310RA020 TG 24 MS 231, MS 231 C, MS 251, MS 251 C
Instruction Manual
Page 27
...in the relaxed condition. Troubleshooting, b 3.2 TOP 2310RA043 TG : Attach the spring (1) to check free travel is the distance the lockout lever (1) can be tightly against engine housing (arrows) and the clutch drum must be depressed without the brake lever moving. Release the lockout lever. - Adjust the brake cable, b 5.4.1 - Remove the ...this is in that the open side of the spring hook (arrow) is released. : Carefully press the lockout lever (1) to the brake lever (arrow). 26 MS 231, MS 231 C, MS 251, MS 251 C If the groove in hand guard, b 14 - Free travel -
...in the relaxed condition. Troubleshooting, b 3.2 TOP 2310RA043 TG : Attach the spring (1) to check free travel is the distance the lockout lever (1) can be tightly against engine housing (arrows) and the clutch drum must be depressed without the brake lever moving. Release the lockout lever. - Adjust the brake cable, b 5.4.1 - Remove the ...this is in that the open side of the spring hook (arrow) is released. : Carefully press the lockout lever (1) to the brake lever (arrow). 26 MS 231, MS 231 C, MS 251, MS 251 C If the groove in hand guard, b 14 - Free travel -
Instruction Manual
Page 28
...on the brake cable retainer. 1 2 : Use 6mm open end wrench the set free travel . 1 1 - The brake band (1) must locate snugly against engine housing (arrows) and the clutch drum must rotate freely. 2 1 - Take care not to reduce free travel. : When the setting is correct, tighten down... b 5.4 1 - clockwise to stretch the hose. 2310RA044 TG 2310RA057 TG - Check the brake cable (1) and retainer (2), replace if necessary MS 231, MS 231 C, MS 251, MS 251 C 27 Adjusting brake cable - Reassemble all other parts in that position. Remove the switch lever, b 10.3.1 2 -
...on the brake cable retainer. 1 2 : Use 6mm open end wrench the set free travel . 1 1 - The brake band (1) must locate snugly against engine housing (arrows) and the clutch drum must rotate freely. 2 1 - Take care not to reduce free travel. : When the setting is correct, tighten down... b 5.4 1 - clockwise to stretch the hose. 2310RA044 TG 2310RA057 TG - Check the brake cable (1) and retainer (2), replace if necessary MS 231, MS 231 C, MS 251, MS 251 C 27 Adjusting brake cable - Reassemble all other parts in that position. Remove the switch lever, b 10.3.1 2 -
