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1 Contents Introduction 6 Engine 3 0 Chain Lubrication 54 Safety Precautions 3 3 Specifications 4 3. Engine Engine (USA only) 4 3. Fuel System Ignition System Chain Lubrication Tightening Torques 6 4 Troubleshooting Chart 8 4. Clutch, Chain Drive, Chain Brake, Chain Tensioner 8 4. Rewind Starter Chain Lubrication Ignition System 4.5 Carburetor 4.6 Engine 4 5 Clutch, Chain Drive, Chain Brake and Chain Tensioner 5 5. Clutch Drum / Chain Sprocket 5 5. Chain Catcher Clutch Chain Brake Checking Operation Removing Installing Front Chain Tensioner 5.6 Side Chain Tensioner 6. Muffler/Spark Arresting Screen 3 6. Leakage Test Preparations Pressure Test Vacuum Test Oil Seals Removing and Installing Cylinder Piston Piston Rings Crankshaft Decompression Valve 34 7 Ignition System Spark Plug Boot Ignition Module Testing the Ignition Coil Checking the Wiring Harness Ignition Timing Removing and Installing Flywheel Ignition System Troubleshooting 39 8 Rewind Starter 4 8. General 4 8. Removing and Installing Rope Rotor Segment Starter Rope Elastostart Tensioning Rewind Spring Pawl 48 9 AV Handle System/ Handle Housing Annular Buffers Front Handle Handle Housing Switch Shaft Contact Spring Throttle Trigger/ Interlock Lever Pickup Body Connector/ Suction Hose Valve Worm Oil Pump 57 Fuel System 58. Air Filter 58. Carburetor 59.. Leakage Test 59.. Removing and Installing Adjusting (Carburetor without Limiter Cap) 6..4 Adjusting (Carburetor with Limiter Cap) 6..5 Standard Setting (Carburetor with Limiter Cap) 6.3 Tank Vent 63.4 Pickup Body 64.5 Suction Hose 64.6 Manual Fuel Pump 65.7 Hoses 65.8 Fuel Tank 67 Special Servicing Tools 69 3 Servicing Aids 7 q 00 Andreas Stihl AG & Co., Waiblingen MS 0, 30, 50

2 Introduction This service manual contains detailed descriptions of all the repair and servicing procedures specific to this power tool series. As the design concept of model MS 0, 30 and 50 chainsaws is almost identical, the descriptions and servicing procedures in thus manual generally apply to all three models. Differences are described in detail. You should make use of the illustrated parts lists while carrying out repair work. They show the installed positions of the individual components and assemblies. Refer to the latest edition of the relevant parts list to check the part numbers of any replacement parts. A fault on the machine may have several causes. To help locate the fault, consult the troubleshooting charts for all assemblies and systems in this manual and the "STIHL Service Training System". Refer to the "Technical Information bulletins for engineering changes which have been introduced since publication of this service manual. Technical information bulletins also supplement the parts list until a revised edition is issued. The special tools mentioned in the descriptions are listed in chapter "Special Servicing Tools" of this manual. Use the part numbers to identify the tools in the "STIHL Special Tools" manual. The manual lists all special servicing tools currently available from STIHL. Symbols are included in the text and pictures for greater clarity. The meanings are as follows: In the descriptions: : = Action to be taken as shown in the illustration (above the text) = Action to be taken that is not shown in the illustration (above the text) In the illustrations: Pointer (short arrow) Direction of movement (long arrow) Service manuals and all technical Information bulletins are intended exclusively for the use of STIHL servicing dealers. They must not be passed to third parties. Servicing and repairs are made considerably easier if the clamp () is used to mount the machine on assembly stand () so that one clamp screw engages the outer 0 mm bore (3) in the assembly stand. To service the underside of the machine (e.g. remove the oil pump), turn the machine through 80 degrees and mount it so that one clamp screw engages the inner 0 mm bore () in the assembly stand. Note: Pull the hand guard back against the front handle for this purpose. Always use original STIHL replacement parts. They can be identified by the STIHL part number, the STIH) logo and the STIHL parts symbol ( This symbol may appear alone on small parts. MS 0, 30, 50

3 Safety Precautions If the engine is started up in the course of repairs or maintenance work, observe all local and countryspecific safety regulations as well as the safety precautions and warnings in the owner s manual. Gasoline is an extremely flammable fuel and can be explosive in certain conditions. Improper handling may result in burns or other serious injuries. Warning! Do not smoke or bring any fire, flame or other source of heat near the fuel. All work with fuel must be performed outdoors only. Spilled fuel must be wiped away immediately. MS 0, 30, 50 3

4 3 Specifications 3. Engine MS 0 MS 30 MS 50 Displacement: 35. cm cm cm 3 Bore: 40 mm 40 mm 4.5 mm Stroke: 8 mm 3 mm 3 mm Engine power to ISO 793:.6 kw (. HP) at 9,000 rpm.0 kw (.7 HP) at 0,000 rpm.3 kw (3. HP) at 0,000 rpm Max. permissible engine speed (with bar and chain):,500 rpm 4,000 rpm 4,000 rpm Idle speed:,800 rpm Clutch: Centrifugal clutch without linings Clutch engages at: 4,00 rpm Crankcase leakage test at gauge pressure: 0.5 bar under vacuum: 0.5 bar 3.. Engine (USA only) MS 0 MS 30 MS 50 Displacement:.5 cu. in.45 cu. in.77 cu. in Bore:.57 in.57 in.67 in Stroke:.0 in.6 in.6 in Engine power to ISO 793:.5 kw (.0 HP).9 kw (.55 HP). kw (.95 HP) Max. permissible engine speed (with bar and chain):,500 rpm 4,000 rpm 4,000 rpm Idle speed:,800 rpm Clutch: Centrifugal clutch without linings Clutch engages at: 4,00 rpm Crankcase leakage test at gauge pressure: 7.5 psi under vacuum: 7.5 psi 4 MS 0, 30, 50

5 3. Fuel System Carburetor leakage test at gauge pressure: Function of tank vent at gauge pressure: Fuel: 0.8 bar (.6 psi) 0.3 bar (4.35 psi) 0.05 bar (0.7 psi) see owner s manual 3.3 Ignition System Air gap between ignition module and fanwheel: Spark plug (resistor type): Electrode gap: 3.4 Chain Lubrication mm ( in) Bosch WSR 6F NGK BPMR 7A 0.5 mm (0.0 in) Fully automatic speed-controlled oil pump with rotary piston Oil delivery rate: approx. 7.5 cc/min (0.46 cu in/min) at 0,000 rpm MS 0, 30, 50 5

6 3.5 Tightening Torques DG screws are used in the polymer and light-alloy components. These screws form a permanent thread when they are installed for the first time. They can be removed and installed as often as necessary without detrimentally affecting the strength of the screwed assembly, providing the specified tightening torque is observed. For this reason always use a torque wrench. Fastener Thread size For component Torque Remarks kpm Nm Spline screw IS-M4x5 Cain brake cover 0..0 Spline screw IS-D4x5 Handle molding Spline screw IS-P5x6 Connector (engine housing/oil pump) Spline screw IS-M4x5 Ground wire (to cylinder) Spline screw IS-DG5x4 Handle housing/front handle Spline screw IS-DG5x4 Hand guard Spline screw IS-DG5x4 Fan housing Spline screw IS-DG5x4 Buffer (to front handle) Spline screw IS-DG5x4 Buffer (to engine housing) Spline screw IS-DG5x4 Ignition module (to engine housing) Spline screw IS-DG5x4 Cylinder (to engine housing) Collar screw DG 8x8 Guide bar mounting.6 6 Collar screw (rear) DG8x8 Guide bar mounting Mx Carrier (clutch) M4x.5 Spark plug.5 5 Collar locknut M5 Muffler Collar locknut M5 Filter housing/carburetor Collar nut M8x Flywheel to crankshaft.8 8 Mx.5 Decompression valve.4 4 Spline screw IS-DG5x6 Spiked bumper MS 0, 30, 50

7 Use the following procedure to fit a DG screw in an existing thread: Place the DG screw in the hole and rotate it counterclockwise until drops down slightly. Tighten the screw clockwise to the specified torque. This procedure ensures that the screw engages properly in the existing thread and does not form a new thread, which would weaken the assembly. Note: Power screwdriver speed setting for polymer: DG screws max. 500 rpm MS 0, 30, 50 7

8 4 Troubleshooting Chart 4. Clutch, Chain Drive, Chain Brake, Chain Tensioner Condition Cause Remedy Saw chain stops under load at full throttle Clutch shoes badly worn Clutch drum badly worn Install new clutch Install new clutch drum Brake band stuck Check freedom of movement and function of brake band Saw chain rotates at idle speed Engine idle speed too high Readjust with idle speed screw (counterclockwise) Clutch springs stretched or fatigued Clutch spring hooks broken Replace the clutch springs Replace the clutch springs Loud noises Clutch springs stretched or fatigued Replace all clutch springs Needle cage damaged Clutch shoe retainer broken Clutch shoes and carrier worn Fit new needle cage Fit new retainer Install new clutch Chain sprocket wears rapidly Chain not properly tensioned Tension chain as specified Saw chain does not stop immediately when brake is activated Wrong chain pitch Brake spring stretched or broken Brake band stretched / worn / broken Fit chain of correct pitch Fit new brake spring Fit new brake band 8 MS 0, 30, 50

9 4. Rewind Starter Condition Cause Remedy Starter rope broken Rope pulled out too vigorously as far as stop or over edge, i.e. not vertically Fit new starter rope Normal wear Fit new starter rope Rewind spring broken (rope does not rewind) Starter rope can be pulled out almost without resistance (crankshaft does not turn) Starter rope is difficult to pull and rewinds very slowly Spring overtensioned no reserve when rope is fully extended Very dirty or corroded Guide peg on pawl or pawl itself is worn Spring clip fatigued Starter mechanism is very dirty (dusty conditions) Lubricating oil on rewind spring becomes viscous at very low outside temperatures (spring windings stick together) Fit new rewind spring Clean or replace rewind spring Fit new pawl Fit new spring clip Thoroughly clean complete starter mechanism Apply a few drops of kerosine (paraffin) to spring, then pull rope carefully several times until normal action is restored MS 0, 30, 50 9

10 4.3 Chain Lubrication Important! In the event of trouble with the chain lubrication system, always investigate the other possible sources of faults before disassembling the oil pump. Condition Cause Remedy Chain receives no oil Oil tank empty Fill up with oil Oil inlet hole in guide bar is blocked Intake hose or pickup body (strainer) clogged or intake hose ruptured Valve in oil tank blocked Teeth on pump piston and/or worm worn Clean oil inlet hole Wash intake hose and pickup body (strainer) in fresh STIHL cleaner or replace if necessary Clean or replace valve Install new oil pump and/or new worm Machine losing chain oil Oil seal leaking Replace oil seal Oil pump delivers too little oil Bore in pump housing worn Control screw and/or control edge on pump piston worn Bore in pump housing worn Fit new pump housing / oil pump Fit new control screw and/or new pump piston Fit new pump housing / oil pump 0 MS 0, 30, 50

11 4.4 Ignition System Warning! Exercise extreme caution while carrying out maintenance and repair work on the ignition system. The high voltages which occur can cause serious or fatal accidents! Condition Cause Remedy Engine runs roughly, misfires, temporary loss of power Spark plug boot is loose Press boot firmly onto spark plug and fit new spring if necessary Spark plug sooted, smeared with oil Weak spark or no spark Incorrect air gap between ignition coil and flywheel Flywheel cracked or has other damage Crankcase damaged (cracks) No ignition spark Clean the spark plug or replace if necessary Faulty insulation on ignition lead or short circuit wire. Use ohmmeter to check ignition lead for break. If break is detected or high resistance measured, fit a new ignition lead Set air gap correctly Install new flywheel Install new crankcase Check operation of Master Control lever, ignition module and ignition lead MS 0, 30, 50

12 4.5 Carburetor Condition Cause Remedy Carburetor floods; engine stalls Inlet needle not sealing. Foreign matter in valve seat or cone damaged Remove and clean or replace the inlet needle, clean the fuel tank, pickup body and fuel line if necessary Inlet control lever sticking on spindle Free off inlet control lever Helical spring not located on nipple of inlet control lever Perforated disc on diaphragm is deformed and presses constantly against the inlet control lever Inlet control lever too high (relative to design position) Remove the inlet control lever and refit it correctly Fit a new metering diaphragm Set inlet control lever flush with top edge of housing or metering chamber face Poor acceleration Idle jet too lean Back off low speed screw (L) slightly Main jet too lean Inlet control lever too low (relative to design position) Inlet needle sticking to valve seat Connecting bore to atmosphere blocked Diaphragm gasket leaking Metering diaphragm damaged or shrunk Back off high speed screw (H) slightly Set inlet control lever flush with top edge of housing or metering chamber face Remove inlet needle, clean and refit Clean bore Fit a new diaphragm gasket Fit a new metering diaphragm MS 0, 30, 50

13 Condition Cause Remedy Engine will not idle, idle speed too high Throttle shutter opened too wide by idle speed screw (LA) Reset idle speed screw (LA) correctly Engine leaking Seal the engine Engine stalls at idle speed Idle jet bores or ports blocked Clean jet bores and ports with compressed air Engine speed drops quickly under load low power Idle jet too rich Setting of idle speed (LA) incorrect throttle shutter completely closed Small plastic plate in valve jet does not close Air filter plugged Tank vent faulty Leak in fuel line between tank and fuel pump Pump diaphragm damaged or fatigued Main jet bores or ports blocked Fuel pickup body dirty Fuel strainers dirty Screw down low speed screw (L) slightly Set idle speed screw (LA) correctly Clean or renew valve jet Clean or renew the air filter Clean tank vent or replace if necessary Seal connections or install new fuel line Fit a new pump diaphragm Clean the bores and ports Clean the pickup body, fit a new filter Clean the fuel strainers MS 0, 30, 50 3

14 4.6 Engine Always check and, if necessary, repair the following parts before looking for faults on the engine: Air filter Fuel system Carburetor Ignition system Condition Cause Remedy Engine does not start easily, stalls at idle speed, but operates normally at full throttle Engine does not deliver full power or runs erratically Engine overheating Oil seals in crankcase damaged Gasket on carburetor spacer flange leaking Engine pan leaking Crankcase damaged (cracks) Muffler leaking Secondary air seepage through leaking gaskets on carburetor spacer flange Piston rings worn or broken Muffler / spark arresting screen carbonized Air filter element dirty Fuel / impulse line severely kinked or damaged Decompression valve sticking Insufficient cylinder cooling. Air inlets in fan housing blocked or cooling fins on cylinder very dirty Replace the oil seals Fit a new gasket Seal the engine pan Replace the crankcase Seal or replace the muffler Fit new gaskets Fit new piston rings Clean the muffler (inlet and exhaust), replace spark arresting screen Replace air filter element Replace lines or position them free from kinks Replace the decompression valve Thoroughly clean all cooling air openings and the cylinder fins 4 MS 0, 30, 50

15 5 Clutch, Chain Drive, Chain Brake and Chain Tensioner 5. Clutch Drum / Chain Sprocket 43RA004 43RA007 Remove the chain sprocket cover. : Disengage the chain brake by pulling the hand guard toward the front handle. : Remove the E-clip (). : Remove the washer (). : Take the needle cage out of the sprocket. Clean and inspect the clutch drum / chain sprocket. 80% 00% : Inspect the clutch drum () for signs of wear. If there are noticeable wear marks on the inside diameter of the clutch drum, check its wall thickness. If it is less than 80% of the original wall thickness, fit a new clutch drum. If the clutch drum has to be replaced, also check the brake band see 5.4.! 48RA0 : If the clutch drum/chain sprocket is still serviceable, use No. 0 emery paper or emery cloth (grain size approx. 0 µm) to clean and roughen its friction surface. Reassemble in the reverse sequence. Clean stub of crankshaft. Wash needle cage in clean white spirit and lubricate with grease see 3. Replace damaged needle cage. Rotate clutch drum/chain sprocket and apply slight pressure at the same time until oil pump drive spring engages properly. If rim sprocket was fitted, reinstall it with the cavities facing outward. Remove the rim sprocket, if fitted. : Pull off the clutch drum / chain sprocket. MS 0, 30, 50 5

16 5. Chain Catcher 5.3 Clutch Troubleshooting chart see 4.. Remove the clutch drum/chain sprocket see 5.. Remove the air filter see.. 08RA RA003 : Sprocket cover with integrally molded chain catcher. If the chain catcher has broken off, repair as follows: : Remove the chain bumper strip (). : Pry the plug () out of the front right-hand AV element. 08RA000 : Oil the cylindrical part () of the replacement chain catcher. : Push the chain catcher into the AV element () and engage the peg (3) in the housing bore (4) at the same time. Fit the chain bumper strip. Assemble all other parts in the reverse sequence. : Take out the shutter. Pull boot off the spark plug. Unscrew the spark plug. 35RA0 Close the decompression valve, if fitted. : Push the locking strip () into the cylinder. 6 MS 0, 30, 50

17 3 35RA03 : Unscrew the clutch from the crankshaft clockwise (left-hand thread). Disassembling the clutch: : Use hook () to remove the clutch springs (). Pull the clutch shoes off the carrier. 08RA03 08RA08 : Pull the retainers, if fitted, off the clutch shoes. Clean all parts with STIHL cleaner. Replace any damaged parts. 08RA06 08RA03 08RA09 : On retainers with tabs (), the narrow side () must be next to the series number (3). 3 : Fit the clutch shoes over the arms () of the clutch carrier so that the series number () is on the same side as the larger hexagon (3). 08RA07 08RA030 Assembling the clutch: : Clamp the clutch in a vise. : Slip the retainers onto the clutch shoes. MS 0, 30, 50 7

18 5.4 Chain Brake 5.4. Checking Operation 08RA033 50RA008 The chain brake is one of the most important safety devices on the chainsaw. Its efficiency is measured in terms of the chain braking time, i.e. the time that elapses between activating the brake and the saw chain coming to a complete standstill. The shorter the braking time, the better the efficiency and protection offered against being injured by the rotating chain. : Attach one end of each spring () to the clutch shoes. : Use the hook () to attach other ends of springs and press them firmly into the clutch shoes. : Screw on the clutch and tighten down to 50 Nm (37 lbf.ft). Install the clutch drum / chain sprocket see RA04 Remove locking strip from the cylinder. Insert spark plug and tighten down to 5 Nm (8.5 lb.ft). : If spark plug has a separate terminal nut, make sure it is properly tightened down. Fit boot on the spark plug. Contamination (with chain oil, chips, fine particles of abrasion, etc.) and smoothing of the friction surfaces of the brake band and clutch drum impair the coefficient of friction. This, in turn, reduces the frictional forces and thus prolongs the braking time. A fatigued or stretched brake spring has the same negative effect. Start the engine. With the chain brake activated (locked), open throttle wide for a brief period (max. 3 seconds) the chain must not rotate. With the chain brake released, open throttle wide and activate the brake manually the chain must come to an abrupt stop. The braking time is in order if deceleration of the saw chain is imperceptible to the eye. : Fit the shutter so that its lugs engage the recesses in the handle housing. Install the air filter see.. 8 MS 0, 30, 50

19 5.4. Removing Remove the clutch drum / chain sprocket see 5.. Release brake spring tension by pushing hand guard forward. Remove upper bumper strip from the tensioner. 35RA07 35RA08 : Take out the screws. Remove the cover. 35RA06 : Pry the brake band out of the engine housing. Disconnect the brake band from the bell crank. Install a new brake band if: there are noticeable signs of wear (large areas on inside diameter and/or parts of outside diameter) and its remaining thickness is less than 0.6 mm (0.04"). Important! Thickness of brake band must not be less at any point. : If the brake band is still serviceable, use No. 0 emery paper or emery cloth (grain size approx. 0 µm) to clean and roughen its entire friction surface (inside diameter). 70RA04 : Remove the screw (arrow) from the hand guard. : Remove the E-clip. 35RA09 35RA030 : Carefully ease the brake spring off the anchor pin and take it off the bell crank. : Remove strap from bell crank pivot pin (). : Push the strap sideways and lift it off the hand guard pivot pin (). MS 0, 30, 50 9

20 5.4.3 Installing Lubricate sliding and bearing points of chain brake with STIHL multipurpose grease or, preferably, molybdenum grease (e.g. Molykote) see 3. Install the flat spring. 35RA03 : Remove the washer. : Carefully pry the hand guard () and bell crank () off their pivot pins and lift away together. Pull the bell crank out of the hand guard. 35RA03 : Remove the flat spring. Inspect parts and replace if damaged. Clean the entire housing recess for the chain brake. If the groove of the brake spring anchor pin is worn, replace the housing. : Insert the bell crank in the side of the hand guard so that the short arm of the bell crank points to top of hand guard. 35RA034 0 MS 0, 30, 50

21 08RA09 35RA03 35RA038 : Position the hand guard () against the pivot pin and fit the other side of the hand guard over the housing. : Position the bell crank () against the pivot pin. : Push the hand guard and bell crank onto their pivot pins. 35RA036 : Fit the washer. : Fit strap on the pivot pin () and engage it in the pivot pin's groove. : Slip the other end of the strap over the bell crank pivot pin (). Secure strap with E-clip. Coat the brake band with chain oil (STIHL Bioplus), see 3, to protect it from corrosion and help reduce "snatching" during the first few brake applications. 35RA037 : Hook the brake spring onto the bell crank. : Position the brake band around the clutch and push it into the engine housing. 35RA039 35RA040 : Check that flat spring () is properly located on face () of hand guard bearing boss. : Attach the brake spring to the bell crank. MS 0, 30, 50

22 5.5 Front Chain Tensioner 5.6 Side Chain Tensioner 35RA04 35RA043 35RA044 : Use the hook () to attach the brake spring () to the anchor pin. Fit the bushing () in the hand guard (). : Insert M5x4 screw (3) and tighten down to 3.5 Nm (.6 lbf.ft). Fit the cover. 3 Tighten screws to.0 Nm (.5 lbf.ft). Fit upper bumper strip on tensioner. Install clutch drum/chain sprocket see 5.. Check operation of chain brake see RA004 Remove the chain sprocket cover. : Pull the cover out of the housing. 3 : Unscrew the nut () from the adjusting screw (). : Take the adjusting screw out of the cover (3). Reverse the above sequence to install the chain tensioner. 43RA05 Remove the chain sprocket cover. : Take out the screw. Pull tensioner assembly out of the engine housing. 4 3 : Take the thrust pad () off the adjusting screw (). : Rotate the spur gear (3) until the adjusting screw comes out of the tensioner slide (4). : Pull the spur gear out of the cover. 35RA045 35RA046 MS 0, 30, 50

23 6 Engine 6. Muffler/Spark Arresting Screen This machine does not have a conventional crankcase. The engine consists of the cylinder, piston, crankshaft and engine pan. Troubleshooting chart see RA047 35RA05 : Pull the tensioner slide off the cover. Take the adjusting screw out of the cover. Inspect the teeth on the spur gear and adjusting screw. Replace both parts if necessary. Reverse the above sequence to install the chain tensioner. Coat teeth of adjusting screw and spur gear with grease, see 3, before refitting. : Unscrew the nuts. Remove the muffler. 35RA048 08RA006 : Muffler with push-fit upper and lower casings: Remove the upper casing from the lower casing. : Muffler with push-fit upper and lower casings: If necessary, take the baffle out of the lower casing. 35RA05 35RA053 : Pull off or lever off the cover plate depending on type fitted. : Remove the gasket () and heat shield (), if fitted. Remove spark arresting screen, if fitted. Clean the screen or fit a new one if necessary. MS 0, 30, 50 3

24 6. Leakage Test 6.. Preparations Defective oil seals and gaskets or cracks in castings are the usual causes of leaks. Such faults allow supplementary air to enter the engine and upset the fuel-air mixture. : Remove the screws from the flange. Reassemble in the reverse sequence. Use a new gasket. Fit new locknuts and torque down to 8.0 Nm (5.9 lbf.ft). 35RA054 This makes adjustment of the prescribed idle speed difficult, if not impossible. Moreover, the transition from idle speed to part or full throttle is not smooth. The engine housing can be checked thoroughly for leaks with the carburetor and crankcase tester and the vacuum pump. Remove the muffler see 6.. : Fit the sealing plate () between the mounting screws. The sealing plate must completely fill the space between the two mounting screws. : Slip the flange () over the screws. : Fit the sleeves (3) on the screws. : Fit the nuts (4) and tighten down securely. Remove the carburetor see... Set the piston to top dead center (T.D.C.). This can be checked through the inlet port. 35RA056 : Inspect carburetor gasket and fit a new one if necessary. 4 MS 0, 30, 50

25 6.. Pressure Test 08RA007 : Fit the test flange () in place of the carburetor. : If decompression valve is fitted, pull out the button. Check that spark plug is properly tightened down. Perform leakage test with tester and vacuum pump Carry out preparations see 6... : Connect pressure hose of tester to nipple on test flange. : Close the vent screw () on the rubber bulb. Pump air into the engine housing with the rubber bulb until the gauge indicates a pressure of 0.5 bar (7.5 psi). If this pressure remains constant for at least 0 seconds, the engine or decompression valve, if fitted, is airtight. 43RA046 : However, if the indicated pressure drops, the leak must be located and the faulty part replaced. To find the leak, coat the suspect area with oil and pressurize the engine again. Bubbles will appear if a leak exists. If the decompression valve is leaking, fit a new one see 6.9. Repeat the pressure test. Carry out the vacuum test see After finishing the test, open the vent screw and disconnect the hose. Remove the test flange. Install the carburetor see... Remove the flange. Remove the sealing plate. Install the muffler see 6.. MS 0, 30, 50 5

26 6..3 Vacuum Test 6.3 Oil Seals Oil seals tend to fail when subjected to a vacuum, i.e. the sealing lip lifts away from the crankshaft during the piston's induction stroke because there is no internal counterpressure. An additional test can be carried out with the vacuum pump to detect this kind of fault. Carry out the preparations see 6... : Connect suction hose of vacuum pump to test flange nipple. 3 35RA06 If the vacuum reading remains constant, or rises to no more than 0.3 bar (4.5 psi) within 0 seconds, it can be assumed that the oil seals are in good condition. However, if the pressure continues to rise (reduced vacuum in the engine housing), the oil seals must be replaced. After finishing the test, open the vent screw and disconnect the hose. Remove the test flange. Install the carburetor see... Remove the flange. Remove the sealing plate. Install the muffler see 6.. It is not necessary to disassemble the complete engine housing if only the oil seals have to be replaced. Clutch side: Remove the clutch see 5.3. Remove the oil pump see 0.5. : Ease the retaining ring out of the crankshaft. 35RA06 : Close the vent screw () on the pump. : Operate the lever () until pressure gauge (3) indicates a vacuum of 0.5 bar (7.5 psi). 6 MS 0, 30, 50

27 35RA063 43RA064 35RA064 : Apply puller () (jaws with No. 6 profile). Clamp the puller arms. Pull out the oil seal. Take care not to damage the crankshaft stub. : If an oil seal with clamping ring () is installed, use puller and No. 3. jaws to remove the clamping ring. Pry the sealing ring () out of the housing. Clean sealing face with STIHL cleaner see 3. If the cylinder and engine pan are assembled, only oil seal (with clamping ring) may be installed. Lubricate sealing lip of oil seal with grease see 3. Thinly coat the outside diameter of the oil seal with sealant see 3. Place the oil seal in position with the clamping ring faces up. : Use the press sleeve () to install the oil seal. Wait about one minute, then rotate the crankshaft. Fit a new retaining ring. Install the oil pump see 0.5. Install the clutch see 5.3. Ignition side: Remove the flywheel see RA065 : Apply puller () (jaws with No. 6 profile). Clamp the puller arms. Pull out the oil seal. MS 0, 30, 50 7

28 6.4 Removing and Installing Take care not to damage the crankshaft stub. Remove oil seal with clamping ring as described for clutch side. Cleaning sealing face with STIHL cleaner see 3. If the cylinder and engine pan are assembled, only oil seal (with clamping ring) may be installed. Lubricate sealing lip of oil seal with grease see 3. Thinly coat the outside diameter of the oil seal with sealant see 3. 35RA066 : Use the press sleeve () to install the oil seal. Wait about one minute, then rotate the crankshaft. Install the flywheel see RA067 Always check and, if necessary, repair the fuel system, carburetor, air filter and ignition system before looking for faults on the engine. Remove the handle housing see 9.3. Remove the oil pump see 0.5. : Pull off the worm with drive spring. 35RA068 35RA069 : Place the oil seal () in position with the clamping ring facing up. : Take out the ground wire fastening screw. : Screw the guide sleeve () onto the crankshaft. 8 MS 0, 30, 50

29 6.5 Cylinder 35RA070 35RA07 : Unscrew the engine pan mounting screws. : Remove engine sideways from housing. Install in the reverse sequence. Tighten down the engine pan mounting screws to 9.5 Nm (7 lbf.ft) and the ground wire fastening screw to 3.5 Nm (.6 lbf.ft). Remove the engine see 6.4. Take out the spark plug. : Remove baffle plate. : Pull the manifold () off the intake port. : Disconnect the impulse hose (). 35RA073 35RA074 : Lift the crankshaft and pull the piston out of the cylinder at the same time. Inspect ball bearings and oil seals and replace if necessary see 6.8. Inspect the cylinder and replace it if necessary. : On easy start version, unscrew the decompression valve. If a new cylinder has to be installed, always fit the matching piston. Replacement cylinders are only supplied complete with piston for this reason. Thoroughly clean all residue of sealant from the cylinder and engine pan mating faces. Apply a thin coating of sealant to the outer diameters of the oil seals see 3. : Pull the engine pan off the cylinder. Lubricate piston and piston ring with oil. MS 0, 30, 50 9

30 35RA080 : Position the piston rings so that the radii at the ring gap meet at the fixing pin in the piston groove when the rings are compressed. : Slide piston carefully into the cylinder. The piston rings are compressed by the inner taper of the cylinder. 35RA079 : Position the crankshaft so that the long crankshaft stub () points to the right, looking at exhaust port (). Push piston home until ball bearings are seated. 35RA08 : Fit the engine pan so that the seat () for the oil pump is at the same side as the long crankshaft stub (). : On easy start version, unscrew the plug, screw home the decompression valve and tighten it to 4 Nm (0.3 lbf.ft). : Apply a thin bead of sealant to the engine pan mating face see 3. Follow manufacturer s instructions for use of sealant. : Push the manifold on to the intake port so that the straight faces are in alignment. Assemble all other parts in the reverse sequence. 30 MS 0, 30, 50

31 6.6 Piston 35RA085 35RA087 Pull the piston out of the cylinder see 6.5. : Ease the hookless snap rings out of the grooves in the piston bosses. : Use the assembly drift () to push the piston pin () out of the piston. If the piston pin is stuck, release it by tapping the end of the drift lightly with a hammer. Hold the piston steady during this process to ensure that no jolts are transmitted to the connecting rod. Remove the piston from the connecting rod. Inspect needle cage and replace if necessary. If needle cage is press-fitted, replace the crankshaft. : Inspect piston rings and replace if necessary see 6.7. : Fit needle cage (arrow) in the connecting rod (not MS 0). Oil the needle cage. : Push the assembly drift, small diameter first, through the piston and small end (needle cage) and line up the piston. : Fit the piston pin () on the assembly drift () and slide it into the piston (the pin slides home easily if the piston is warm). a b 35RA093 : To ease assembly, heat the piston slightly and push it over the connecting rod. Installed position of piston: = Arrow = Long stub of crankshaft : Modify sleeve of the installing tool as shown: a = 6 mm (/6") b = 8 mm (5/6") MS 0, 30, 50 3

32 49RA44 : Remove the sleeve from the tool. : Attach the snap ring () to the magnet () so that the snap ring gap is on the flat side of the tool's shank. 49RA45 49RA47 49RA46 : Stand the installing tool, sleeve downward, on a flat surface (wooden board) and press vertically downwards until the sleeve butts against the tool's shoulder. : Remove the sleeve and slip it onto the other end of the shank. Inner pin must again point toward flat face. 49RA48 49RA50 49RA49 Fit the snap rings so that their gaps are on the piston's vertical axis (they must point either up or down see arrow). Install the piston see 6.5. : Push the large slotted diameter of the sleeve over the magnet and snap ring. Position the sleeve so that the inner pin () points toward the flat face () of tool's shank. : Apply the installing tool to the piston boss, hold the piston steady, center the tool shank exactly and press home until the snap ring slips into the groove. 3 MS 0, 30, 50

33 6.7 Piston Rings 6.8 Crankshaft Pull the piston out of the cylinder see 6.6. Remove rings from the piston. 35RA097 : Use a piece of old piston ring to scrape the grooves clean. 35RA095 35RA096 : The crankshaft () and connecting rod are an inseparable unit. This means the crankshaft must always be replaced as a complete unit. The needle bearing () is replaceable on models MS 30 and MS 50. When fitting a replacement crankshaft, always install new ball bearings and oil seals. 70RA096 : Pull off the oil seals () and ball bearings (). : Heat ball bearing to approx. 50 C (0 F) and, with closed side facing outwards, push it on to the crankshaft stub as far as stop. If the crankshaft has been removed, the oil seals used in production ( with rigid housing) may be installed. Lubricate sealing lips of oil seals with grease see 3. 35RA00 : Install the new piston rings in the grooves so that the radii face upward. Install the piston see 6.6. Remove the piston see 6.6. : Remove the retaining ring (arrow). MS 0, 30, 50 33

34 6.9 Decompression Valve 7 Ignition System Exercise extreme caution when troubleshooting and carrying out maintenance or repair work on the ignition system. The high voltages which occur can cause serious or even fatal accidents!! 35RA0 Troubleshooting on the ignition system should always begin at the spark plug see 4.4. : Slide oil seals over the crankshaft stubs so that their open sides are facing the ball bearings. Install new retaining ring in crankshaft groove. Install the piston see 6.6. Remove the front handle see 9.. : Use standard 3 mm socket to unscrew the decompression valve. Install new decompression valve and torque down to 4 Nm (0.5 lbf.ft). Refit the front handle. The electronic (breakerless) ignition system basically consists of an ignition module () and flywheel (). 35RA06 34 MS 0, 30, 50

35 7. Spark Plug Boot 7. Ignition Module Remove the air filter see.. Pull out the shutter see 5.3. Pull boot off the spark plug. The ignition lead is molded to the module. 35RA08 08RA008 : Use pliers to grip the leg spring and pull it out of the spark plug boot. Unhook the leg spring from the ignition lead. Pull the spark plug boot off the ignition lead. Coat end of the ignition lead (about 0 mm/3/4") with oil. Fit spark plug boot over the ignition lead. Use pliers to grip the end of the ignition lead inside the spark plug boot and pull it out. 35RA07 : Pinch the hook (arrow) of the leg spring into the center of the lead, i.e. about 0 mm (3/8") from the end of the lead. : Pull the lead back into the boot so that the leg spring locates properly inside it (see arrow). If the spark plug has a separate terminal nut, make sure that it is properly tightened down. Fit boot on the spark plug. Fit the shutter see 5.3. Install the air filter see.. 7RA46 The ignition module accommodates all the components required to control ignition timing. There are two electrical connections on the coil body: : the high voltage output with ignition lead (), : the connector tag () for the short circuit wire. Accurate testing of the ignition module is only possible with a special tester. For this reason it is only necessary to carry out a spark test in the workshop. A new ignition module must be installed if no ignition spark is obtained (after checking that wiring and stop switch are in good condition). MS 0, 30, 50 35

36 7.3 Testing the Ignition Coil 7.4 Checking the Wiring Harness To test the ignition module, use either the ZAT 4 ignition system tester or the ZAT 3 ignition system tester The ignition test refers only to a spark test, not to ignition timing. Before starting the test, check that the spark plug is in good condition. Test the ignition coil only with the spark plug properly installed in the cylinder. : Using the ZAT 4 ignition tester : Pull the boot off the spark plug and connect it the input terminal (). Push the tester s output terminal (3) onto the spark plug. Pull the rewind starter and check the sparkover in the tester s window (). 3 08RA053 ZAT It is necessary to use the ZAT 3 ignition system tester to test the auxiliary spark gap. Before starting the test, install a new spark plug in the cylinder and tighten it down firmly see 3.5. : Pull the boot off the spark plug boot and connect it to terminal (). : Attach ground terminal () (alligator clip) to spark plug. Use adjusting knob (3) to set spark gap to about mm. While using the ZAT 3, hold it only by the handle or position it in a safe place. Warning! High voltage risk of electrocution. Crank engine with rewind starter (min.,000 rpm) and evaluate spark in spark window. 3 If a spark is visible, the ignition system is in order. If no spark is visible, check the wiring harness and contact spring see RA054 If the spark plug, ignition lead and spark plug boot are in order, use an ohmmeter to check the short circuit wire, ground wire and contact spring for a break. : Pull the short circuit wire (arrow) off the tag on the ignition module. Connect ohmmeter to ground and the short circuit wire. Set Master Control lever to "0". The measured resistance must be about 0 Ohm. If the reading is much higher, there is a break in the wire and the wire or Master Control lever must be replaced. Set Master Control lever to "". The measured resistance must be infinitely high. If not, install a new Master Control lever. 35RA 36 MS 0, 30, 50

37 7.4. Ignition Timing 7.4. Removing and Installing If no fault is found, perform the following additional checks: Check flywheel for damage see Check air gap between flywheel and ignition module see 7.5. If no fault is detected in these areas either, install a new ignition module see Ignition timing is not adjustable. Since there is no mechanical wear in these systems, ignition timing cannot get out of adjustment. However, an internal fault in the circuit can alter the switching point in such a way that a spark test will still show the system to be in order although timing is outside the permissible tolerance. This will impair engine starting and running behavior. Remove the fan housing see 8.. : Pull the short circuit wire off the tag on the ignition module. : Take out the screws (arrows). 35RA 35RA 08RA0 Pull the ignition module forward a little. : Take the short circuit wire () out of the retainer (). MS 0, 30, 50 37

38 7.5 Flywheel 35RA6 : Push baffle plate () in direction of fanwheel and carefully pull out the ignition lead (). Place the module in position, insert the screws but do not tighten them down yet. : Secure ground wire () with outer screw. : Slide the setting gauge () between the arms of the ignition module and the flywheel magnet poles. Press the ignition module against the setting gauge and tighten down the mounting screws to 4 Nm (3 lbf.ft). Reassemble all other parts in the reverse sequence. Removing the flywheel: Fit the locking strip to block the piston see 5.3. Remove the fan housing see 8.. Unscrew the flywheel nut. Pull off the flywheel. 35RA7 Inspect flywheel () and magnet poles () for cracks or other damage. If you find any damage, install a new flywheel. Installing the flywheel: Degrease crankshaft stub and bore in flywheel with STIHL cleaner see 3. Fit the flywheel. Check position of slot. Assemble all other parts parts in the reverse sequence. Tighten the flywheel nut to 8 Nm (0.6 lbf.ft). If the flywheel cannot be removed by hand, screw on the puller () and tap its end to release the flywheel. Remove the puller. 38 MS 0, 30, 50

39 7.6 Ignition System Troubleshooting Engine does not run Master Control lever/slide control or separate stop switch in position ""? Check the spark plug: Smeared with oil, black? Sooted? Electrode gap correct? Contacts shorted? Clean the plug, reset or replace Check spark plug boot: Firmly seated on plug (leg spring)? Leg spring hook in center of ignition lead? Boot damaged? If necessary, install new spark plug boot and/or leg spring Test ignition system with ZAT3 or ZAT4 (use ZAT 3 as main spark gap see TI 3.94) MS 0, 30, 50 39

40 Powerful spark? yes no Check air gap and reset if necessary Check flywheel: Have pole shoes turned blue? Install new flywheel Disconnect short circuit wire from ignition module Check ignition lead: Severe chafing? Spark plug boot: Holes/cracks? Resistance spark plug boot to ground: spec..5 kω Check resistance of ignition lead: spec. < 0 Ω, If necessary, install new spark plug boot and/or ignition lead 3 40 MS 0, 30, 50

41 3 yes Check operation of Master Control lever/slide control or separate stop switch Short circuit wire chafed? Contact gap (contact springs) If necessary, install new ignition lead and/or contact springs Re-connect short circuit wire Powerful spark? Install new ignition module Engine runs no yes no Check ON/STOP function on Master Control lever/ slide contro or separate stop switch Look for fault in fuel system or carburetor, check engine for leaks, check position of flywheel on crankshaft MS 0, 30, 50 4

42 8 Rewind Starter 8. General 8. Removing and Installing 8.3 Rope Rotor If the action of the starter rope becomes very stiff and the rope rewinds very slowly or not completely, it can be assumed that the starter mechanism is in order but plugged with dirt. At very low outside temperatures the lubricating oil on the rewind spring may thicken and cause the spring windings to stick together. This has a detrimental effect on the function of the starter mechanism. In such a case it is sufficient to apply a few drops of paraffin (kerosine) to the rewind spring. Carefully pull out the starter rope several times and allow it to rewind until its normal smooth action is restored. If clogged with dirt or pitch, the entire starter mechanism, including the rewind spring, must be removed and disassembled. Take special care when removing the spring. Wash all parts in STIHL cleaner. Lubricate the rewind spring and starter post with STIHL special lubricant, see 3, before installing. : Remove the screws (arrows) from the fan housing and hand guard. Lift away the fan housing with rewind starter. Reassemble in the reverse sequence. Tighten down screws to 6 Nm (4.4 lbf.ft). 08RA00 Troubleshooting chart see 4.. Remove the fan housing see 8.. Relieving tension of rewind spring: The rewind spring will not be under tension if the starter rope is broken. Pull out the starter rope about 5 cm (") and hold the rope rotor steady. While still holding the rope rotor steady, take three full turns off the rope rotor. Pull out the rope with the starter grip and slowly release the rope rotor. 08RA034 Removing the rope rotor: : Use a screwdriver or suitable pliers to carefully remove the spring clip from the starter post. 4 MS 0, 30, 50

43 08RA035 49RA4 08RA036 : Remove the washer (arrow). : Carefully pull the rope rotor off the starter post. To replace the rope rotor, first remove the starter rope see 8.5. The rewind spring may pop out and unwind if rope rotor is not removed very carefully. 08RA037 Installing the rope rotor: Coat bore in rope rotor with STIHL special lubricant see 3. : Fit the rotor on the starter post so that the lug () on the rope rotor slips behind the inner spring loop (). Check that spring loop has engaged by turning rope rotor slightly and letting it go it must spin back. Fit washer and push the spring clip into the groove in the starter post. Make sure the spring clip () engages the pawl guide peg () and points in the clockwise direction. The spring clip must be handled very carefully. If it is bent during disassembly or assembly, the rewind starter may not function properly. Install the starter rope see 8.5. Tension the rewind spring see MS 0, 30, 50 43

44 8.4 Segment 8.5 Starter Rope Remove the rope rotor see 8.3. Remove the rope rotor see 8.3. Remove the remaining rope from the rope rotor and the starter grip. 35RA9 : Use a screwdriver to pry the segment () out of the upper retainers (4). Pull the segment upwards and remove. Reassemble in the following sequence. : Place the segment () in position and push it under the retainer (). : Engage lugs (3) flush with housing. : Push segment into retainers (4). Reassemble all other parts in the reverse sequence. : Thread end of new rope through the hole in the side of the rotor, pull it out. Secure the rope with a simple overhand knot. 08RA038 08RA040 : Thread the other end of the rope through the guide bush from inside. : Then through the underside of the starter grip and pull it out. 08RA0039 : Pull the rope back until the knot locates in the recess (arrow) in the rope rotor. 44 MS 0, 30, 50

45 8.5. Elastostart 98RA036 08RA05 08RA049 : Tie one of the special knots shown. Pull the rope back into the starter grip. Install the rope rotor see 8.3. Tension the rewind spring see : Pry the nipple of the starter rope out of the starter grip. Pull out the starter rope. : Thread new starter rope through the top of the starter grip. 08RA05 : Thread the other end of the rope, from outside, through the guide bush in the fan housing. Fit the rope in the rope rotor see 8.5. Install the rope rotor see 8.3. Fit the fan housing see RA050 : Pull out the starter rope until the nipple () locates in the starter grip. MS 0, 30, 50 45

46 8.5. Tensioning 08RA0 08RA04 35RA : Make a loop in the starter rope. : Grip the rope next to the rotor and use it to turn the rope rotor six times clockwise. 08RA03 : Hold the rope rotor steady. : Pull out the rope with the starter grip and straighten it out. Hold the starter grip firmly to keep the rope tensioned. Let go of the rope rotor and slowly release the starter rope so that it can rewind properly. The rewind spring is correctly tensioned when the starter grip sits firmly in the rope guide bush without drooping to one side. If this is not the case, tension the spring by one additional turn. When the starter rope is fully extended, it must still be possible to rotate the rope rotor at least another half turn before maximum spring tension is reached. If this is not the case, pull the rope out, hold the rope rotor steady and take off one turn of the rope. Do not overtension the rewind spring as this will cause it to break. Fit the fan housing see MS 0, 30, 50

47 8.6 Rewind Spring Remove the rope rotor see 8.3. The replacement spring comes ready for installation and is secured with a frame. a 43RA Lubricate the spring with a few drops of STIHL special lubricant before installation see 3. : The frame () slips off as the rewind spring is pushed into the fan housing. Press the anchor loop () into the recess in the fan housing at the same time. The rewind spring may pop out and uncoil during installation. If the rewind spring has popped out, refit it in the assembly tool as follows: : Position the anchor loop about 0 mm (3/4") (dimension 'a') from the edge of the assembly tool. : Fit the rewind spring in the counterclockwise direction, starting from outside and working inwards. Place wooden block over the assembly tool to simplify this operation. Slip the assembly tool with rewind spring over the starter post. 43RA : Push the rewind spring into the fan housing and then remove the assembly tool. Install the rope rotor see 8.3. Tension the rewind spring see 8.6. MS 0, 30, 50 47