Stihl 028 038 Chainsaw Full Service & Repair Manual

F SERVICE MANUAL 028/038 FOREWORD This Service Manual covers model 028 chain saws up to machine number 5561640 as well as later machines unless technical information bulletins have been issued in the meantime with updated repair procedures. Models 038 have substantially the same constructional features as model 028 chain saws" This Serv- ice Manual can therefore be used for the 038 chain saws as well. In the event of faults it is quite pos-, sible that a single malfunction may have several causes. It is, therefore, advisable to consult the "troubleshooting charts" when tracing faults" We also recommend that you make use of the exploded views in the illustrated parts lists while carrying out repair work. This service manual and all technical information bulletins are in- tended exclusively for the use of STIHL servicing staff and dealers and must not be passed on to third parties. STI H L® Andreas Stihl Postfach 1760 Repair work is made considerably easier if the chain saw is mounted on assembly stand 59108503100. The saw is easily attached to the stand by means of the two stud bolts and collar nuts for bar mount- ing" While on the assembly stand, the chain saw can be swivelled into any required position to suit the repair in question" This not only has the advantage of keeping the compo- nent in the best position for the repair, but also leaves both hands free for the work, and thus repre- sents a considerable time-saving. 0-7050 Waiblingen SPECIAL TOOL MANUAL 1 Our special tool manual illustrates and lists the part numbers of all available machine-related tools as well as general purpose tools for all machines. The special tool manual is available in various languages and can be ordered by quoting the appropriate part number listed hereunder. German English French Spanish Yugoslav Swedish Italian Portuguese 0455 901 0023 04559010123 0455 901 0223 0455 901 0323 0455 901 0423 0455901 0523 0455 901 0723 0455 901 1223

p 2 CONTENTS 1 . Specifications 4 4 .. Ignition System 26 4 .. 5 .. 1 Checking on breaker- 4.1 Construction 26 controlled ignition 45 4 .. 2 Operation 26 4.5.2 Adjustment on breaker- 2 .. Clutch, Chain Drive 4 . .2 .. 1 General information 26 controlled ignition 45 and Chain Brake 7 4.2.2 Breaker-controlled 4 .. 5 .. 3 Checking on electronic 2.1 Construction magneto ignition 27 ignition 47 and operation 7 4 . .2 .. 3 Bosch transistor-controlled 4.6 Magneto edge gap 48 2 .. 1.1 Clutch and chain sprocket 7 magneto ignition 28 2 .. 1.2 Chain brake 8 4.2.4 SEM thyristor-controlled 2.2 Troubleshooting chart 8 magneto ignition 29 2.3 Disassembly and repair 9 4 .. 2.4..1 Charging the storage 5 .. Rewind Starter 49 2 .. 3.1 Clutch 9 capacitor 29 5 .. 1 Construction 2.3 . .2 Chain brake 12 4.2 .. 4.2Triggering the thyristor 29 and operation 49 2.4 Assembly 13 4 . .2.4..3 Ignition 30 5.2 Troubleshooting chart 49 2.4.1 Chain brake 13 4 .. 3 Troubleshooting chart 31 5.3 Disassembly 50 2.4 . .2 Clutch 14 4.3.1 Breaker-controlled 5.4 Replacing the starter ignition system 31 rope 50 4 .. 3 . .2 Electronic ignition 5.5 Replacing the rewind 3 .. Engine 15 system 32 spring 51 3.1 Construction 15 4.4 Function and repair 5 .. 6 Tensioning the rewind 3.2 Troubleshooting chart 15 of components 33 spring 51 3 .. 3 Exposing the cylinder 16 4.4..1 Spark plug 33 5.7 Replacing starter rope 3.4 Disassembly of cylinder 4.4..2 Ignition lead 34 guide bush 52 and piston 16 4 .. 4.3 Short-circuit wire/ground 5 .. 8 Routine maintenance 52 3.5 Assembly of piston wire 35 and cylinder 17 4.4.4 Short-circuit contact 36 3 .. 6 Disassembly of crankcase 4.4.5 Flywheel 37 - removal of crankshaft 19 4 .. 4.6 Armature (Bosch)/ignition 6 .. AV Handle System 53 3 . .7 Installing the Crankshaft module (SEM) 39 6 .. 1 Construction - assembly of crankcase21 4.4..6 .. 1 Resistance test on and operation 53 3.8 Leakage testing primary winding 39 6 . .2 Repair 53 the crankcase 23 4.4..6.2Resistance test on 3 .. 8.1 Pressure test 23 secondary winding 39 3 . .8.2 Vacuum test 25 4.4..6 .. 3 Ignition coil tester 40 3.8 .. 3 Replacing the oil seals 25 4.4..6.4 Disassembly 7 .. Master Control 55 and assembly 40 7.1 Construction 4.4.7 Condenser 41 and operation 55 4.4.8 Contact set 42 7 . .2 Disassembly 4.4..9 Trigger plate 44 and assembly 55 4 .. 5 Ignition timing 44

8" Electric Handle Heating System 56 8,,1 Construction and operation 56 8.2 Troubleshooting 56 8,,3 Disassembly and assembly 58 8.3.1 Switch 58 8,,3,,2 Heating element in pistol grip 58 8.3.3 Handlebar 58 8,,3..4 Generator 59 9" Chain Lubrication 60 9.1 Construction and operation of oil pump 60 9,,2 Troubleshooting chart 61 9,,3 Oil tank/tank vent 62 9..4 Repair of pickup body and valve 62 9.5 Disassembly and repair of oil pump 63 1O" Fuel System 64 1 0,,1 Construction and operation of carburetor 64 10"1,, 1 Operation of fuel pump 64 1 0.1,.2 Operation of carburetor 64 10,,2 10,,3 10..4 10.5 10,,6 10,,6,,1 Troubleshooting chart 66 Leakage test on carburetor 68 Disassembly of carburetor 68 Repair of carburetor 69 Carburetor adjustment 71 Notes for fine adjustment of carburetor 71 3 10.7 Fuel line and tank vent 71 10.8 Air filter and choke 72

4 1. SPECIFICATIONS 1.1 Engine 1.2 Fuel System STIHL single cylinder, two-stroke engine with special impregnated cylinder bore Displacement: Bore:. Stroke: Compression ratio:: Max. torque: Max. permissable engine speed: Mean idle speed: Crankshaft: Crankshaft bearings: Crankpin: Big-end bearing: Piston pin: Small-end bearing: Rewind starter: Starter rope: Clutch: Clutch engages at: Crankcase leakage test: with overpressure:: with vacu u m: Carburetor: Adjustment: high-speed adjustment screw H: low-speed adjustment screw L: Carburetor leakage test with overpressure: Fuel capacity: 47 cm 3 (2 .. 87 tu. in) 44 mm (1.73 in) 31 mm (1.22 in) 9.5:1 2 .. 65 Nm (1..95 Ibf. ft) at 6000 rpm 12000 rpm 2200 rpm Two-part, drop-forged 2 deep-groove ball bearings 14..4 mm (0.57 in) dia. Needle cage 10 .. 0 mm (0 .. 39 in) dia. Needle cage Pawl engagement with automatic starter rope rewind mechanism 3.5 mm (0 .. 14 in) dia., 1060 mm (41.8 in) long Centrifugal clutch without linings, 76 mm (3 in) dia. Approx. 3100 rpm po = 0 .. 5 bar (7 .. 1 Ibf/in2) pu = 0.5 bar (7.1 Ibflin2) All-position diaphragm carburetor with integral fuel pump Open approx. 11/4 turns Open approx .. 1114 turns (basic setting with screws initially hard against their seats) po = 0.4 bar (5 .. 7 Ibflin2) 0.52 L (1..1 U.S.pt)

1.3 Ignition System Fuel mixture: Air filter:: 028 AV and 028 AVQ Type: Magneto edge gap: Air gap: Ignition timing: Ignition advance angle: Breaker point gap:: Condenser: Armature: 028 AVE Type: Air gap: Ignition timing:: Ignition advance angle: Armature: 028 AVEQ Type: Air gap: Ignition timing: All Models Spark plug (suppressed): Spark plug thread: Fuel mix 1 :40 with STIHL two-cycle engine oil; 1:25 for other branded two-cycle engine oils Flat wire mesh filter Breaker-controlled magneto ignition system 4 .. " 8 mm (0,,16 . " . 0.31 in) 0,,2 ... 0.3 mm (0.008" " . 0.012 in) 2.2 .. ,,2,,3 mm (0.087" , ,,0.091 in) before T..D"C. 27"".28° 5 0.35 ... 0.4 mm (0.014. , .0.016 in) Capacitance 0.15" " . 0.19 IlF Coil resistors Primary 0..7 ... 1,,00 Secondary 7..7 ... 10.3 kQ Transistor-controlled (breaker- less) magneto ignition system 0.2. " . 0,,3 mm (0,,008,. , 0.012 in) 2.6 mm (0,,1 in) before T.D.C" at 8000 rpm 30° at 8000 rpm as 028 AV/028 AVQ Thyristor-controlled (breaker- less) magneto ignition system 0,,2 ... 0.3 mm (0.008 ... 0,,012 in) 2.6 mm (0,,1 in) before T.D.C" at 8000 rpm Bosch WSR 6 F or Champion RCJ 6 Y Heat range: 200 Electrode gap:: 0.5 mm (0,,02 in) M 14x1..25; 9.5 mm (0.37 in) long

6 1.4 Tightening Torques Crankshaft nut (ignition side) M 8 x 1: 30 Nm (22 Ibf. ft) Hub/spider (output side):, 50 Nm (37 Ibf. ft) M 5 socket head screws: 8 Nm (6 Ibf.. ft) M 5 cheese-head screws: 5 Nm (3,,7 Ibf. ft) M 4 cheese-head screws:, 2.5 Nm (1.8 Ibf.. ft) M 5 nuts: 5 Nm (3.7 Ibf.. ft) Spark plug: 25 Nm (18,,4 Ibf.. ft) Important: The M 5 x 12 screws on the front handguard and the M 4 x 8 screws on the spider are fitted with LOCTITE. 1.5 Cutting Attachment Guide bars:, STIHL Duromatic guide bars with stellite-tipped bar nose; STIHL Rollomatic guide bars with sprocket nose. Both types with corrosion resistant finish and induction hardened track Bar lengths: Duromatic 40 and 45 cm (16 and 18 in) Rollomatic 32, 37, 40 and 45 cm (13,14.6,16 and 18 in) Chain:, 0.325" (8,,25 mm) pitch Chain sprocket:: 7 -tooth for 0.325" chain Chain speed:, 16.4 m/s (53.8 ft/sec) at 8500 rpm Chain lubrication:, Speed-controlled oil pump with lift plunger, operative only when chairi is running Oil delivery rate: 8 cm3 /min (0,,49 cu. in/m in) at 6000 rpm Oil tank capacity:, 0.3 L (0,,63 U"S"pt) 1.6 Weights Model: AV/AVE AVQ/AVEQ Dry weight with 32 cm bar and chain:, 6,,5 kg (14.3 Ib) 6,,6 kg (14.5 Ib) 1,,7 Special Accessories STIHL rescue kit 028 11189005000 Gasket set 028 11180071050

2. CLUTCH, CHAIN DRIVE AND CHAIN BRAKE 2 .. 1 Construction and Operation 2 .. 1 .. 1 Clutch and Chain Sprocket The transmission of power from the engine to the saw chain is effected via a centrifugal clutch .. O~ "Quick- stop" models, the centrifugal clutch incorporates an isolating clutch which isactuated by the chain brake. On the Quickstop version the hub screwed to the crankshaft is the clutch element which absorbs the torque and acceleration of the crankshaft.. It is essential that the hub is always tightened down to the specified torque .. The clutch spider is supported on the hub by a needle sleeve and located axially with a circlip .. The driving plate is located on thethree lugs of the clutch spider and can move axially while remai- ning in constant mesh with the spider .. The flat spring between the spider and driving plate presses the driving plate against the release plate; this means that the internal teeth of the driving plate are always in mesh with the teeth of the hub when the chain brake is released, and thus provides positive transmission of engine torque to the clutch spider .. When the chain brake is actuated, the release plate disengages the driving plate from the hUb .. The clutch spider and hub can then rotate independently. On the standard version the clutch spider assumes the function of the hub and must therefore always be tightened to the specified torque .. Chain brake engaged The centrifugal clutch has three clutch shoes without linings .. The clutch drum and chain sprocket are separate components. The spur gear which drives the oil pump is a ring-gear, positively mounted to the hub of the clutch drum .. The chain sprocket has two integrally cast lugs which engage in corresponding re- cesses on the drum hub .. As the lugs have odd sizes, the chain sprocket can only be fitted in one position .. When the engine is running at idle speed the clutch shoes are also in the idle position, because the tension of the clutch spring is greater than the centrifugal force .. As engine speed increases, centrifugal force presses the clutch shoes outwards against the clutch drum and thus transmit engine torque positively via the chain sprocket to the saw chain .. The preload and strength of the clutch spring are designed so that 7 Chain brake released the clutch shoes begin to make contact with the clutch drum at an engine speed of approx .. 3100 rpm (engagement speed) .. The clutch engages fully above this speed .. The correct idle setting on the carburetor is therefore essential in order to insure that the clutch engagement speed is not reached when the engine is idling ..

8 2,,1,,2 Chain Brake The chain brake is a spring-loaded band brake without linings" Its main components are the brake band, tension spring, handguard and release plate - which operates the isolating clutch" The chain brake is actuated by means of the handguard which can be used to release and engage the brake" 2.2 Troubleshooting Chart Fault Saw chain turns at idle speed The chain brake is released (reset) by pulling the handguard back against the handlebar" This movement is transmitted via a lever system which preloads the tension spring and disengages the brake band. At the same time the release plate moves back and allows the driving plate to engage in the teeth of the hub" The brake lever, which is connected to the tension spring, brake band and release plate, is locked in the idle position by the relay lever. Cause Engine idle speed too high Clutch spring stretched or fatigued, spring hooks broken Excessive chain sprocket wear Incorrect chain tension Chain stops in mid-cut even with Isolating clutch worn engine at maximum speed - Isolating clutch disengages Flat spring broken during cutting Isolating clutch does not re-engage Engine idle speed too high after releasing chain brake Flat spring broken Saw chain does not stop imme- Tension spring broken diately when chain brake is engaged The chain brake is actuated by mo- ving the handguard towards the bar nose" This movement unlatches the brake lever and causes the brake band to be clamped around the clutch drum by the force of the pre- loaded brake spring" The release plate simultaneously disengages the driving plate from the hub and interrupts the flow of power between the crankshaft and the centrifugal clutch" Clutch drum and saw chain are brought to a standstill within a fraction of a second even if the engine continues running at high speed" Remedy Readjust at idle speed adjustment screw Renew clutch spring Tension saw chain properly Renew hub and driving plate Renew flat spring Readjust at idle speed adjustment screw Renew flat spring Renew tension spring

2,,3 Disassembly and Repair 2,,3,,1 Clutch Top: Chain brake released Bottom: Pressing out the retaining washer First remove chain sprocket cover and cutting attachment.. The chain brake must be released before removing the chain sprocket Use a screwdriver, about 5 mm wide, to press the retaining washer out of the annular groove in the crankshaft. The thrust washer, chain sprocket and needle sleeve can now be pulled off the crankshaft Top: Removing the side plate Center: Releasing the cover Bottom: Ring-gear removed 9 Top: Removing the spur gear Bottom: Clutch drum and needle sleeve removed Remove the inner side plate - se- cured with a single M 4 x 12 cheese- head screw" Unscrew the five M 4 x 12 cheese-head screws and take off the cover" Now remove ring gear from clutch drum hub and the spur gear (with worm) from the oil pump shaft by turning it clockwise. Pull clutch drum and needle sleeve off the crankshaft

Stihl 028 038 Chainsaw Full Service & Repair Manual

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