4-CYCLE OVERHEAD VALVE ENGINES - Small Engine Discount

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GENERAL INFORMATION OPERATION CHAPTER 6 ELECTRICAL SYSTEMS The electrical system consists of three main elements: a battery, a starting circuit, and a charging circuit. The battery is part of both the starting and charging circuit. The battery should be checked before going into any extensive starter or charging system checks. If a battery has a shorted cell, overcharging can result, and the regulator or rectifier may appear to be at fault. If a cell has an open or high resistance connection, the electric starter operation will be affected. The power source used to provide the energy to turn an electric starter motor on Tecumseh engines is either 120 volt A.C. current or 12 volt D.C. A 120 volt A.C. starter circuit utilizes a 120 volt power source instead of a battery. The 12 volt battery models require a charging system to maintain proper battery charge. The starting circuit includes the battery, battery cables, starter or ignition switch, safety switches, starter solenoid, and an electric starter motor. The charging system consists of alternator charge coils, rectifiers or diodes, regulator, ignition switch, flywheel magnets, and a battery. All engines that have a charging system will use a combination of some or all of these features. STARTING CIRCUIT AND ELECTRIC STARTERS After all of the safety interlock switches have been activated, the starter switch closes the starting circuit. A strong magnetic force is produced by the electrical BOLT current running through the armature windings. The BRUSHES armature magnetism repels the magnetism produced by the permanent field magnets of the electric starter. BRUSH SPRINGS The repelling magnetic forces cause the armature to BRUSH CARD rotate, moving the drive pinion laterally on the splined HOUSING armature shaft, meshing the starter pinion gear with the flywheel ring gear. When the drive pinion contacts the stop at the end of the armature shaft, the pinion rotates along with the armature shaft to crank the engine. The armature and pinion remain positively engaged until the engine fires and the flywheel rotates SPRING faster than the armature. The greater momentum of RETAINER the flywheel throws the starter pinion gear out of mesh and forces the starter pinion back to the disengaged RETAINER position. After the switch is released, the starting GEAR SPRING circuit is opened and the armature coasts to a stop. DUST COVER A small anti-drift spring holds the pinion in the disengaged position (diag. 1). LOCK NUT END CAP END CAP WASHER NUTS ARMATURE THRUST WASHER ENGAGING NUT 1 CHARGING CIRCUIT The charging system works independently of any manual controls. The engine needs to be running to produce an electric current flow. When a conductor (alternating coils) cuts the magnetic field generated by the magnets in the flywheel, a current is induced in the alternator coil. The permanent magnets in the flywheel have a magnetic field in which the lines of magnetic force run from the North Pole to the South Pole. As the flywheel rotates and the position of the magnets change, the direction of the magnetic field changes or alternates. The alternating coils are wound in different directions to allow current to flow as an A.C. waveform (diag. 2). ROTATION OF FLYWHEEL Not For Resale www.SmallEngineDiscount.com 2 35
CONVERTING ALTERNATING CURRENT TO DIRECT CURRENT ANODE CATHODE In order to charge a battery, it is necessary to convert alternating current (A.C.) to direct current (D.C.). This is accomplished by using a diode or rectifier (diag. 3). A single diode makes use of only one half of the A.C. signal and is known as HALF WAVE RECTIFICATION (diag. 4). This is acceptable in certain applications. In certain situations it is necessary to make use of the entire A.C. signal. To accomplish this, multiple diodes in a bridge configuration are used to produce FULL WAVE RECTIFICATION (diag. 5). BAND OR OTHER MARKING INDICATES CATHODE END 3 Current flows through a diode when the anode is more positive than the cathode. The cathode end of the diode should point toward the battery when diode is used between a charging system and a battery. Half Wave Rectifier Single Diode The single diode allows only the positive half of the A.C. signal through. It does not allow the negative portion through. + VOLTAGE HALF WAVE RECTIFIER (SINGLE DIODE) + VOLTAGE - VOLTAGE A.C. INPUT - VOLTAGE D.C. OUTPUT 4 Full Wave Rectifier Bridge Rectifier The full wave rectifier makes use of the entire A.C. signal, converting it to D.C. + VOLTAGE FULL WAVE RECTIFIER (BRIDGE RECTIFIER) COMPONENTS - VOLTAGE A.C. INPUT BATTERY The batteries used in conjunction with Tecumseh engines are 12 volt lead acid or “maintenance free” style. The chemical energy produced by the dissimilar metals of the battery plates provides a electrical potential that is used to power the electric starter or unit accessories. Consult the original equipment manufacturer’s service manual for battery size, capacities, and testing procedure. A.C. INPUT + VOLTAGE - VOLTAGE D.C. OUTPUT + VOLTAGE (D.C.) 5 WIRING The wires used in Tecumseh electrical systems are copper stranded with an insulated coating around the copper strands. CONDITION: All wiring must be fully insulated between connection points, securely fastened and free of foreign material (such as rust and corrosion) at the connection points. This is especially important in the use of batteries where much of the potential may be lost due to loose connections or corrosion. Remember to check the insulation on the wire. All it takes is a pin hole for leakage to "ground out" on the engine or frame. This is of special concern when moisture or water is present. 36 Not For Resale www.SmallEngineDiscount.com
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Page 3 and 4: Page TESTING PROCEDURE ............
Page 5 and 6: SHORT BLOCKS SBV OR SBH IDENTIFICAT
Page 7 and 8: STORAGE (IF THE ENGINE IS TO BE UNU
Page 9 and 10: TROUBLESHOOTING OR TESTING If the e
Page 11 and 12: 8 CHAPTER 3 CARBURETORS AND FUEL SY
Page 13 and 14: CARBURETOR VISUAL IDENTIFICATION Se
Page 15 and 16: TESTING 12 1. After repeated effort
Page 17 and 18: If further adjustment is required,
Page 19 and 20: FLOAT ADJUSTING PROCEDURE All Tecum
Page 21 and 22: ASSEMBLY PROCEDURE Welch Plugs To i
Page 23 and 24: Inlet Needle and Seat Make sure the
Page 25 and 26: 22 CHAPTER 4 GOVERNORS AND LINKAGE
Page 27 and 28: Governor Shaft Replacement, Retaini
Page 29 and 30: NOTE: Early production OHH engines
Page 31 and 32: OVM, OVXL, OHV VERTICAL SPEED CONTR
Page 33 and 34: CAUTION: HANDLE MATCHES SAFELY TO A
Page 35 and 36: 32 4. Use a small Phillips screwdri
Page 37: Stylized Starter (OHV 13.5 -17) 34
Page 41 and 42: TROUBLESHOOTING ELECTRICAL STARTER
Page 43 and 44: TESTING PROCEDURE STARTING CIRCUIT
Page 45 and 46: 3 AMP DC ALTERNATOR SYSTEM - DIODE
Page 47 and 48: CHECKING THE SYSTEM: To check the s
Page 49 and 50: 10 Amp A.C. Alternator CHECKING THE
Page 51 and 52: LOW OIL PRESSURE SENSOR Test the se
Page 53 and 54: CHAPTER 7 FLYWHEEL BRAKE SYSTEMS GE
Page 55 and 56: BRAKE BRACKET ASSEMBLY Late product
Page 57 and 58: The flywheel with magnets provide t
Page 59 and 60: SERVICE To remove the ignition modu
Page 61 and 62: CHAPTER 9 INTERNAL ENGINE AND CYLIN
Page 63 and 64: COMPONENTS The cylinder block house
Page 65 and 66: ENGINE OPERATION PROBLEMS ENGINE MI
Page 67 and 68: ENGINE VIBRATES EXCESSIVELY 64 1. R
Page 69 and 70: 10. Remove the flywheel key and alt
Page 71 and 72: CYLINDERS Visually check the cylind
Page 73 and 74: PISTONS, RINGS, AND CONNECTING RODS
Page 75 and 76: Mechanical Compression Release (MCR
Page 77 and 78: CRANKCASE BREATHERS The breather el
Page 79 and 80: SERVICE BUSHING We are supplying th
Page 81 and 82: 8. Mount the cylinder cover or flan
Page 83 and 84: 13. On engine models OHH and OVRM,
Page 85 and 86: 22. Attach the fuel tank (if applic
Page 87 and 88: 84 ENGINE SPECIFICATIONS OVRM40 OVR
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OVERHEAD VALVE TORQUE SPECIFICATION
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CHAPTER 11. EDUCATIONAL MATERIALS A
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OIL SEAL DRIVER OIL SEAL REMOVER No
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