Makita EM4251 Service Manual

OHV Petrol Engine Service ManualModel: EM4250, EM4251

P 7 / 45 4. GENERAL DESCRIPTION OF ENGINE COMPONENTS4 - 1 Cylinder and CrankcaseThe cylinder and crankcase are aluminum die castings split in upper a

P 8 / 45 4 - 4 Piston RingsThe piston rings are made of special iron. The top ring is a barrel face one, the second ring is a tapered one, and the oi

P 9 / 45 4 - 8 Ignition System4 - 9 Carburetor4 - 10 Air CleanerThe ignition system is a TIC flywheel magneto type one. The ignition timing is 25 deg

P 10 / 45 4 - 12 Sectional View of EngineOil GaugeCheck BallMufflerMufflerCoverConnecting RodExhaust ValveIntake ValveBreather PipeCarburetorAir Clean

P 11 / 45 4 - 12 Sectional View of EngineOil TubeRecoil StarterCam GearPiston PinPiston RingPistonPush RodRocker ArmSpark PlugIgnition CoilFlywheelFue

P 12 / 455. DISASSEMBLING AND REASSEMBLING5 - 1 Preparations and Suggestions5 - 2 Procedures for Disassembling(1) When disassembling the engine, memor

P 13 / 452Air Cleaner, Insulator,Insulator carburetor,1) Remove air cleaner cover and element. See Fig.5-6. 1) Remove separator plate. See Fig.

P 14 / 453Step Parts to be removed Remarks and procedures FastenersMuffler and Muffler CoverRecoil StarterFuel TankPulleyRemove muffler cover from muf

P 15 / 454Step Parts to be removed Remarks and procedures FastenersBlower housingBlower housingClutchRemove blower housing from cylinder and crank cas

P 16 / 45 5Step Parts to be removed Remarks and procedures FastenersFlywheelIgnition coilSpark plugRemove flywheel from crankshaft.* After taking off

CONTENTS - 1/2Section Title Page1 1SPECIFICATIONS OF ENGINE2 2PERFORMANCE3 4FEATURES4 7GENERAL DESCRIPTION OF ENGINE COMPONENTS5 12DISASSEMBLING AND R

P 17 / 456Step Parts to be removed Remarks and procedures FastenersOil caseOil tube and Retainer plateAfter taking off screws M5x18, remove oil case f

P 18 / 45 7Step Parts to be removed Remarks and procedures FastenersRocker coverRocker armCam gear cover Cam lifter, Cam gear and Push rodRemove rock

P 19 / 45 Recoil sideRecoil sideSocket head bolt M5x14 : 8 pcs. Cylinder blockFig.5-198Step Parts to be removed Remarks and procedures Fasten

P 20 / 45 9Step Parts to be removed Remarks and procedures FastenersValve, Valve spring and Spring retainerHold intake and exhaust valves from the ins

P 21 / 4510Step Parts to be removed Remarks and procedures FastenersPiston and Piston ring1) Take off clips from piston pin. So, piston pin can be

P 22 / 455 - 3 Procedures for Reassembling* Precautions for reassembling1) Clean parts thoroughly before reassembling. Pay most attention to keep cl

P 23 / 45 5 - 3 - 2 Connecting rod, Piston and Piston ringInstalling the piston on the connecting rod(1) After installing piston rings, apply 4-cycle

P 24 / 45 5 - 3 - 3 Cylinder block and CrankcaseInstalling cylinder block and crankcaseTightening torque of hexagonal socket head bolts(8 pcs.) for fa

P 25 / 45 5 - 3 - 4 Oil CaseInstalling oil case Install the lead valve with the cutout facing the oil pouring port.Fasten retainer plate with hexagon

P 26 / 455 - 3 - 5 Oil CaseInstalling flywheel5 - 3 - 6 Ignition coilInstalling ignition coil (Air gap adjustment)Air gap : 0.3mmFasten ignition coil

CONTENTS - 2/2Section Title Page4310 TROUBLESHOOTING4411 INSTALLATION10 - 1 Starting Difficulties4311 - 1 Installing4411 - 2 Ventilation4511 - 3 Exhau

P 27 / 455 - 3 - 8 Cam gear5 - 3 - 9 Push rod, Cam lifter and Rocker armInstalling cam gear(1 )Align the mark punched on the flywheel (key position g

P28 / 45 (3) Install rocker arm assembly. When doing so, align push rod point with the ball groove of rocker arm assembly. When installing

P 29 / 45 Screw M5 with washer : 3 pcs.Rocker cover gasketRocker coverFig. 5 - 405 - 3 - 12 Rocker coverBefore installing rocker cover, apply oil on t

P 30 / 455 - 3 - 15 Insulator and carburetor insulatorCover insulator with carburetor insulator and fasten them together, with screw M5 x 18 (2 pcs.)

P 31 / 45 5 - 3 - 16 Carburetor and air cleaner(1) Assemble the following parts. Plate, Choke plate Air cleaner element Carburetor Gask

P 32 / 45 Breather pipeHose clampPlate upper part clawPipeTubeTubeFig. 5 - 46(b) Install the fuel tank tube on the fuel joint of the carburetor. (B

P 33 / 45The tightening torque for bolt M4-16 : 1 - 2 N.m (10 - 20 Kg.cm) (0.7 - 1.4 ft.lb.)The tightening torque for sc

P 34 / 45Oil gaugeFig. 5 - 50Upper limit(Mouth of the oilcharging port)Oil levelFig. 5 - 515 - 3 - 20 Engine oil, Oil gauge(1) Place the engine horizo

P 35 / 456. MAGNETO6 - 1 Flywheel magnetoThe engine system of the EH025 is a contactless magnet T.I.C. Ignition system.6 - 2 Ignition of magnetoWhen t

P 36 / 45 7. Automatic decompression system7 - 1 Functions and construction7 - 2 InspectionThe decompression system is installed on the camshaft for

1. SPECIFICATIONS OF ENGINEP 1 / 45Model No.TypeBore x Stroke 34 mm x 27 mm (1.5/16" x 1-1/16")0.55kW (0.75HP) / 7,000 r.p.m.0.81kW (1

P 37 / 45 8. Carburetor8 - 1 Operation and Construction8 - 1 - 1 Functions and Construction of the Diaphragm systemThis engine is equipped with a dia

P 38 / 45 8 - 2 Disassembly and reassembly1. Screw2. Plug3. Swivel4. Washer5. Spring retaining ring6. Throttle valve assembly7. Carburetor body assem

P 39 / 458 - 2 - 1 Precautions8 - 2 - 2 Procedures for disassembling and reassembling8 - 2 - 3 Precautions for inspection8 - 2 - 4 Marks punched on th

P 40 / 45 9. Recoil starter9 - 1 DisassemblingThe recoil starter presents practically no failure under normal use. When it fails, however, or when ref

p 41 / 459 - 2 Reassembling(1) First, pass starter rope through starter knob and make an overhead knob as shown in Fig. 9 - 3. Next, pass the opp

P 42 / 459 - 3 Check after reassembling9 - 4 Other guides(1) Pull starter rope a few times to check, if: A. Starter knob is too heavy to pull, check

P 43 / 4510. Trouble shooting10 - 1 Starting difficulties10 - 1- 1 Fuel system10 - 1- 2 Compression system10 - 1- 3 Compression system10 - 2 Engine mi

P 44 / 45 10 - 3 Engine stops(1) Fuel tank empty. Water, dirt, gum, etc. in gasoline.(2) Vapor lock, i.e., gasoline evaporating in the fuel lines due

P 45 / 4511 - 3 Exhaust gas discharge Exhaust gas is noxious. When operating the engine indoors, be sure to discharge the exhaust gage outdoor.If a lo

2. PERFORMANCE2 - 1 Maximum OutputThe maximum output is the output of an engine with its throttle valve fully opened under the condition that all the

P 3 / 452 - 4 Performance Curves000.20.40.60.81.00.20.40.60.81.01.2OUTPUT(PS) (kW)(N.m)(kg-m)0.060.080.100.120.60.81.01.2Torque(g/kWh)(g/PSh)250300400

P 4 / 453. FEATURES3 - 1 The Smallest and Lightest 4-Stroke Engine in the Trade1) Small-sized lubricant oil tank. thanks to the lubrication system dev

P 5 / 45 (a) Since the lubricating system operates by making use of the pressure fluctuations in the crankcase, a lead valve is arranged at the lo

P 6 / 45 Fig. 3-2Fig. 3-3(b) When the engine is tilted with the muffler down In the same way as in the case in which the engine tilts with the