CONTENTS
CHAPTER 1 GENERAL INFORMATION 1
ENGINE IDENTIFICATION 1
Tecumseh engine model, specification, and serial numbers or (date of manufacture, DOM) are stamped into the blower housing or located on a decal on the engine in locations as illustrated.
INTERPRETATION OF MODEL NUMBER 1
The first letter designation in a model number indicates basic type of engine.
The number designations following the letters indicate the horsepower or cubic inch displacement.
The number following the model number is the specification number. The last three numbers of the specification number indicate a variation to the basic engine specification.
The serial number or D.O.M. indicates the production date.
SHORT BLOCKS 2
New short blocks are identified by a tag marked S.B.H. (Short Block Horizontal) or S.B.V. (Short Block Vertical). Original model identification numbers of an engine should always be transferred to a new short block for correct parts identification.
FUEL 2
Tecumseh strongly recommends the use of fresh clean unleaded regular gasoline in all engines. Unleaded gasoline burns cleaner, extends engine life and promotes better starting by reducing build-up of combustion chamber deposits.
REFORMULATED AND OXYGENATED FUELS
Reformulated fuels containing no more than 10% Ethanol, 15% MTBE, 15% ETBE or premium gasoline can be used if unleaded regular gasoline is not available. Leaded fuel may be used in countries where unleaded fuel is not available.
NEVER USE FUEL CONTAINING METHANO
ENGINE OIL 3
Use a clean, high quality detergent oil. Be sure original container is marked: A.P.I. service SF thru SJ. The use of multigrade oil may increase oil consumption under high temperature, high load applications.
Change the oil after the first two (2) hours of operation and every 25 hours thereafter, or more often if operated under dusty or dirty conditions, extreme temperature, or high load conditions.
Check the oil each time the equipment is used or every 5 hours. Position the equipment so the engine is level when checking the oil.
TUNE-UP PROCEDURE 3
The following is a minor tune-up procedure. When this procedure is completed, the engine should operate properly. Further repairs may be necessary if the engine's performance remains poor.
STORAGE 4
(IF THE ENGINE IS TO BE UNUSED FOR 30 DAYS OR MORE)
Gasoline can become stale in less than 30 days and form deposits that can impede proper fuel flow and engine operation. To prevent deposits from forming, all gasoline must be removed from the fuel tank and the carburetor. An acceptable alternative to removing all gasoline is adding a fuel stabilizer to the gasoline. Fuel stabilizer (such as Tecumseh's Part No. 730245) is added to the fuel tank or storage container. Always follow the mix ratio found on the stabilizer container. Run the engine at least 10 minutes after adding the stabilizer to allow it to reach the carburetor.
Change Oil: If the oil has not been changed recently, this is a good time to do it.
Clean Engine: Remove the blower housing and clean all dirt, grass or debris from the intake screen, cylinder head,
cylinder cooling fins, carburetor, governor levers and linkage.
CHAPTER 2 AIR CLEANERS 5
The air cleaner is the device used to eliminate dust and dirt from the air supply. Filtered air is necessary to assure that abrasive particles are removed before entering the carburetor and combustion chamber. Dirt allowed into the engine will quickly wear the internal components and shorten the life of the engine.
Tecumseh engines use either a polyurethane or a paper type air filter system. A polyurethane pre-cleaner or a flocked screen may be used in conjunction with the main filter.
Snow King® engines do not use an air filter.
Extremely dirty conditions may require more frequent filter cleaning or replacement.
CHAPTER 3 CARBURETORS AND FUEL SYSTEMS
GENERAL INFORMATION 5
Tecumseh uses two basic types of carburetors, float and diaphragm type carburetors. Float type carburetors use a hollow float to maintain the operating level of fuel in the carburetor. Diaphragm type carburetors use a rubber-like diaphragm.
One side is exposed to intake manifold pressure and the other side to atmospheric pressure. The diaphragm provides the same basic function (maintaining the proper fuel level in the carburetor) as the float.
An advantage of the diaphragm carburetor over the float style is that the diaphragm carburetor will allow the engine to operate at a greater degree of tiltability.
Tecumseh carburetors are identified by a manufacturing number and date code stamped on the carburetor as illustrated.
When servicing carburetors, use the engine model and specification number to obtain the correct carburetor part number. An alternate method of finding the correct carburetor part number is to use the manufacturing number stamped on the carburetor and convert this number to a part number. In the carburetor section of the Master Parts Manual, Microfiche Catalog or computer parts look-up system, a cross reference chart will convert a carburetor manufacturing number to a Tecumseh part number.
Complete carburetor replacement may be accomplished with a standard service carburetor. A standard service carburetor is a basic carburetor that may require the use of original carburetor parts or additional new parts to adapt to the specification.
OPERATION 5
The outer cover encapsulates the air filter element(s) and prevents large particles from entering the filter box. Air is filtered through the pre-cleaner or flocked screen (if equipped) and the polyurethane or paper filter element. Precleaners or flocked screens provide additional air cleaning capacity.
COMPONENTS 5
TROUBLESHOOTING OR TESTING 5
If the engine's performance is unsatisfactory (needs excessive carburetor adjustments, starts smoking abnormally, loses power), the first engine component to be checked is the air cleaner. A dirt restricted or an oil soaked element will cause noticeable performance problems. A polyurethane element may be cleaned following the service procedure listed under "Service" in this chapter. A paper type air filter should only be replaced. A paper-type element cannot have an oil film present on the paper. Follow the procedure listed in the "Service" section of this chapter for replacement. Re-try the engine after filter replacement or service.
SERVICE 6
Service on the polyurethane element (cleaning and oiling) is recommended every three months or every twenty five operating hours, whichever comes first. Extremely dirty or dusty conditions may require daily cleanings.
The paper filter element should be replaced at least once a year or more frequently if operated in dusty or dirty conditions.
DISASSEMBLY PROCEDURE 6
POLYURETHANE-TYPE FILTER ELEMENT 6
This type of air filter can be serviced when restricted with dust or dirt. Wash the filter or pre-cleaner in a liquid detergent and water solution until all the dirt is removed. Rinse in clear water to remove the detergent solution. Squeeze the element (do not twist) to remove the excess water. Wrap the element in a clean cloth and squeeze it (do not twist) until completely dry.
Re-oil the element by applying engine oil and squeezing it vigorously to distribute the oil. Roll the element in a cloth and squeeze it (do not twist) to remove the excess oil.
PAPER-TYPEAIR FILTER ELEMENT 6
Paper type air filter elements can only be serviced by replacement. Do not attempt to clean a paper filter element.
CHAPTER 3 CARBURETORS AND FUEL SYSTEMS 7
GENERAL INFORMATION 7
OPERATION 8
In the “CHOKE” or “START” position, the choke shutter is closed and the only air entering the engine enters through openings around the shutter. As the engine starts to rotate, downward piston travel creates a low air pressure area (or vacuum) above the piston. Higher pressure (atmospheric) air rushes into the engine and fills this low pressure area. Since the majority of the air passage is blocked by the choke shutter, a relatively small quantity of air enters the carburetor at an increased speed. The main nozzle and both idle fuel discharge ports are supplying fuel due to the low air pressure in the engine intake. Maximum fuel flow through the carburetor orifices combined with the reduced quantity of air that passes through the carburetor, make a very rich fuel mixture which is needed to start a cold engine.
At engine IDLE speed, a relatively small amount of fuel is required to operate the engine. The throttle is almost completely closed. Fuel is supplied through the primary idle-fuel discharge orifice.
FUEL PRIMERS 8
Primers may be mounted remotely or as an integral part of the carburetor. The basic function of the primer is to supply a charge of air to the carburetor main well, or carburetor bowl. On diaphragm carburetors it displaces fuel directly into the carburetor venturi. This displaced fuel provides a rich mixture necessary for engines to start easily on the first or second attempt.
IMPULSE FUEL PUMPS 9
Impulse fuel pumps may either be mounted externally onto the carburetor fuel inlet or remotely mounted. These pumps are connected in the fuel line between the fuel supply and the carburetor or directly to the fuel inlet.
FLOAT STYLE CARBURETORS 9
A float is used to maintain the operating volume of fuel in the carburetor bowl. As the fuel is used by the engine, the fuel volume in the carburetor bowl drops and the float moves downward. This allows the inlet needle valve to move off the sealing seat. Fuel flows by gravity or a pulse pump into the fuel bowl. As the fuel volume in the bowl again rises, it raises the float. This upward float motion moves the inlet needle valve to the closed position. When the needle contacts the seat, the fuel flow is stopped. The tapered end of the inlet needle varies the fuel flow rate so that the fuel volume in the carburetor bowl will remain constant (diag. 7). The float height is set according to the service procedure.
DIAPHRAGM CARBURETORS (PRESSURE DIFFERENTIAL) 9
This type of carburetor uses a rubber-like diaphragm which is exposed to intake manifold pressure on one side and to atmospheric pressure on the other. Tecumseh diaphragm carburetors use the diaphragm as a metering device. As the intake manifold pressure decreases due to downward piston travel, the atmospheric pressure on the vented side of the diaphragm moves the diaphragm against the inlet needle. The diaphragm movement overcomes the spring tension on the inlet needle and moves the inlet needle off the seat. This permits the fuel to flow through the inlet valve to maintain the correct fuel volume in the fuel chamber. The inlet needle return spring closes the inlet valve when the pressure on the diaphragm equalizes or a pressure higher than atmospheric exists on the intake side (upward piston travel). The diaphragm meters a correct fuel volume in the fuel chamber to be delivered to the mixing passages and discharge ports.
COMPONENTS 10
CARBURETOR IDENTIFICATION 11
Tecumseh has a variety of carburetors. To help identify these carburetors here are some simple procedures to follow.
DUAL SYSTEM CARBURETORS 11
SERIES 1 CARBURETORS 11
SERIES 3 & 4 CARBURETORS 11
DIAPHRAGM CARBURETORS 11
SERIES 6 CARBURETORS 4-CYCLE 12
SERIES 8 12
SERIES 9 12
SERIES 10 (EMISSION) 12
NON-TECUMSEH CARBURETORS -- DELLORTO CARBURETOR 12
ENGINE TROUBLESHOOTING CHART 13
CARBURETION TROUBLESHOOTING CHART 14
TESTING 15
SERVICE 15
CARBURETOR PRE-SETS AND ADJUSTMENTS 15
FINAL ADJUSTMENTS (NON-EMISSION ENGINES) 16
NON-ADJUSTABLE CARBURETOR 16
DISASSEMBLY PROCEDURE 17
FLOAT STYLE CARBURETORS 17
DIAPHRAGM CARBURETORS 19
FLOAT ADJUSTING PROCEDURE 19
INSPECTION 20
After careful disassembly of the carburetor and the removal of all non metallic parts, the carburetor body and all other metallic parts should be cleaned with solvent, or commercial carburetor cleaner, no longer than 30 minutes. Use compressed air and soft tag wire to clean internal carburetor passages. To do a proper cleaning job, the welch plugs must be removed to expose the drilled passages.
ASSEMBLY 21
STANDARD SERVICE CARBURETORS 24
CHAPTER 4 GOVERNORS AND LINKAGE 26
GENERAL INFORMATION 26
This chapter includes governor assembly and linkage illustrations to aid in governor or speed control assembly.
Tecumseh 4 cycle engines are equipped with mechanical type governors. The governor’s function is to maintain a constant R.P.M. setting when engine loads are added or taken away. Mechanical type governors are driven off the engine’s camshaft gear. Changes in engine R.P.M. cause the governor to move the solid link that is connected from the governor lever to the throttle in the carburetor. The throttle is opened when the engine R.P.M. drops and closes as the engine load is removed.
OPERATION 26
As the speed of the engine increases, the governor weights (on the governor gear) move outward by centrifugal force. The shape of the governor weights force the governor spool to lift. The governor rod maintains contact with the governor spool due to the governor spring tension. As the spool rises, the governor rod rotates, causing the attached outer governor lever to pull the solid link and close the throttle opening. When the engine speed decreases, the lower centrifugal force allows the governor weights to be pulled in by the governor spring. As the spool lowers, the governor rod rotates and the solid link pushes the throttle to a more open position.
INTERNAL COMPONENTS (VARIOUS STYLES) 26
TROUBLESHOOTING 26
Engine problems where the governor is suspected to be the cause, may actually be the result of other engine system problems. Hunting (engine R.P.M. surging up and down) indicates that the engine is incapable of maintaining a constant R.P.M. with or without an engine load. Engine overspeeding (either with or without throttle movement) must be corrected immediately before serious engine damage occurs. Use the following procedure to diagnose a suspected governor problems.
ENGINE OVERSPEEDING 27
ENGINE SURGING 27
SERVICE 27
GOVERNOR ADJUSTMENT 27
GOVERNOR ADJUSTMENT PROCEDURE FOR SHORT BLOCK INSTALLATIONS 27
GOVERNOR GEAR AND SHAFT SERVICE 28
SPEED CONTROLS AND LINKAGE 29
CHAPTER 5 REWIND STARTERS 35
GENERAL INFORMATION 35
Rewind starters used on vertical shaft Tecumseh engines are top mount horizontal pull style or side mount vertical pull style. Horizontal shaft engines use side mounted starters which can be mounted to pull either vertically or horizontally. All rewind starters except the vertical pull style turn the engine over by engaging a dog(s) into the starter cup attached to the engine flywheel. The vertical pull starter engages the starter gear into the ring gear of the flywheel to turn the engine over. All starters are spring loaded to retract the dog(s) or starter gear when the engine speed exceeds the turning speed of the starter.
OPERATION 35
As the starter rope is pulled, the starter pulley rotates on the center pin. The starter dog(s) is pinned or pocketed in the pulley hub and extends outward when the pulley's rotation forces the starter dog(s) to contact the ears on the retainer. The retainer ears act as a ramp to fully extend the starter dog(s). The fully extended starter dog(s) locks in contact with notches in the starter cup. When the engine fires and the rotational speed of the starter cup exceeds the starter pulley, the starter dog(s) disengages from the starter cup. The starter dog spring(s) returns the starter dog(s) to the disengaged position. The recoil spring turns the starter pulley in the opposite direction, retracting the starter rope until the handle contacts the stop.
COMPONENTS 35
SERVICE 35
Starter related problems will require the starter to be removed from the engine to diagnose the cause. Visually inspect the starter dog(s), starter cup, retainer, springs, rope, washers, and the starter pulley for wear or breakage. Use one of the following procedures that applies to your application, to disassemble, repair, and assemble the starter. Always consult the Tecumseh Master Parts Manual for the correct replacement parts.
ROPE SERVICE 35
RETAINER REPLACEMENT 36
STYLIZED REWIND STARTER (TVS, HM, TVM, TVXL), AND STAMPED STEEL STARTER (HM, VM, TVM, TVXL) 36
STYLIZED REWIND STARTER WITH PLASTIC RETAINER 37
STANDARD STAMPED STEEL AND CAST ALUMINUM STARTER (HM, VM) 38
VERTICAL PULL STARTER HORIZONTAL ENGAGEMENT TYPE 39
VERTICAL PULL STARTER VERTICAL ENGAGEMENT TYPE 40
CHAPTER 6 ELECTRICAL SYSTEMS 42
GENERAL INFORMATION 42
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. An 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, 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.
OPERATION 42
STARTING CIRCUIT AND ELECTRIC STARTERS 42
After all of the safety interlock switches have been activated, the starter switch will complete the circuit. A strong magnetic force is produced by the electrical current running through the armature windings. The armature magnetism repels the magnetism produced by the permanent field magnets of the electric starter. The repelling magnetic forces cause the armature to rotate, moving the drive pinion laterally on the splined 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 faster than the armature. The greater momentum of the flywheel throws the starter pinion gear out of mesh and forces the starter pinion back to the disengaged position. After the switch is released, the starting circuit is opened and the armature coasts to a stop. A small anti-drift spring holds the pinion in the disengaged position.
CHARGING CIRCUIT 42
When a conductor (alternating coils) cuts the magnetic field generated by the magnets in the flywheel, a current will be 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.
CONVERTING ALTERNATING CURRENT TO DIRECT CURRENT 43
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.
HALF WAVE RECTIFIER SINGLE DIODE 43
The single diode allows only the positive half of the A.C. signal through. It does not allow the negative portion through.
FULL WAVE RECTIFIER BRIDGE RECTIFIER 43
The full wave rectifier makes use of the entire A.C. signal, converting it to D.C.
COMPONENTS 43
BATTERY 43
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.
WIRING 43
The wires used in Tecumseh electrical systems are copper stranded with an insulated coating around the copper strands.
ELECTRICAL TERMS 44
ALTERNATOR - An alternator consists of coils of wire wound around a metal lamination stack. When a magnet is moved past the coils, a current is induced in the coils. In general, the greater the number of coils, the greater the output of the alternator (diag. 7).
IGNITION COIL - The ignition coil is used to fire the spark plug. It is completely independent from the alternator coils. RECTIFIERS and DIODES - Charging a battery requires that the alternating current produced by the alternator be changed to direct current. This is accomplished by using a diode or rectifier.
REGULATOR/RECTIFIERS - This combines a regulator with a rectifier. The regulator prevents overcharging of the battery and the rectifier changes the alternating current to direct current (diag.8, 9, 10).
CONDUCTORS - A conductor is a material that allows an electric current to pass through it. All metals are conductors of electricity, but some are better conductors than others. Silver, copper and gold are some of the better known conductors. As the temperature of the conductor increases, the resistance increases.
INSULATORS - An insulator is a material that will not allow an electric current to pass through it. Some of the more common materials that are insulators are glass, plastic, rubber, ceramics and porcelain.
BASIC CHECKS 45
TROUBLESHOOTING ELECTRICAL STARTER CIRCUIT FLOW CHART 46
TROUBLESHOOTING ELECTRICAL CHARGING CIRCUIT FLOW CHART 47
TESTING PROCEDURE 48
STARTING CIRCUIT 48
CHARGING CIRCUIT 48
The following pages will show wiring diagrams of several Tecumseh charging systems. The charging system used on the engine is best identified by obtaining the engine model number and the specification number on the engine.
Consult a Tecumseh dealer or a parts manual to identify the charging system. To make many of the tests it is necessary to run the engine and measure alternator output with a voltmeter. When making voltage tests with the engine running, it is not necessary to take readings at all the listed R.P.M.s. Checking at one of the speeds is sufficient.
In some cases an open circuit D.C. check cannot be made. An SCR (Silicon Controlled Rectifier) is located in the circuit which requires a minimum “turn on” voltage to allow it to conduct. Without the battery in the circuit this “turn on” voltage is not present. The SCR “senses” this and there will be no D.C. output from the regulator or rectifier. Each charging system has its own testing procedure.
VOLTAGE REGULATIONS 56
If a known good or load tested battery fails to maintain a charge, the charging system and the regulator can be checked using a voltmeter. Set the voltmeter on the 0-20 Volt D.C. scale and connect the probes across the battery terminals as shown. Note the battery voltage. Start the engine, the voltage reading should increase from the noted battery voltage but not exceed 15 Volts D.C. If no voltage increase is noted, proceed to make an A.C. voltage check using the applicable procedure. If the battery voltage exceeds 15 Volts D.C., or the proper minimum A.C. voltage is noted during the check, replace the regulator.
LOW OIL SHUTDOWN SWITCHES 56
Check the LOS switch while it is in the engine. The engine must be level, and the oil level at the full mark. Place the speed control in the run position. Remove the spark plug wire from the spark plug. Install a gap type tester connected to the spark plug wire and a good engine ground. Spin the engine over using the electric or recoil starter. A bright blue spark should be seen at the tester. If not, remove the blower housing and disconnect the LOS lead from the ignition module. Reinstall the blower housing and spin the engine over. If spark occurs now, replace the LOS switch. If no spark is seen, replace the ignition module.
SERVICE 57
This section covers the service procedures for the 12 and 120 volt electric starters. For diagnosis of the starting circuit see “Electrical Starter Troubleshooting” in this chapter. Illustrations may not be identical in configuration to the starter being serviced, but procedures and tests apply unless otherwise stated.
12 VOLT OR 120 VOLT ELECTRIC STARTERS WITH EXPOSED SHAFT 57
12 VOLT D.C. OR 120 VOLT A.C. ELECTRIC STARTERS WITH THE STARTER GEAR UNDER
THE CAP ASSEMBLY 57
INSPECTION 58
CHAPTER 7 FLYWHEEL BRAKE SYSTEMS 59
GENERAL INFORMATION 59
Tecumseh’s brake systems provide two methods of meeting compliance standards which has become a federal law as of June 30, 1982. There are two additional methods used by equipment manufacturers that also meet compliance standards and they are as follows:
1. Use of the blade brake clutch in conjunction with either a top or side mounted recoil starter or 12 volt electric starter. The blade stops within three seconds after the operator lets go of the blade control bail at the operator position and the engine continues to run. Starter rope handle is either on the engine or on the equipment handle.
2. Use of a recoil starter (top or side mounted) with the rope handle on the engine as opposed to within 24 inches (60.9 cm) of the operator position. This method is acceptable if the mower deck passes the 360 degree foot probe test. A specified foot probe must not contact the blade when applied completely around the entire blade housing. This alternative can be used with engine mounted brake systems and typical bail controls. The blade stops within three seconds after the operator lets go of the engine/blade control bail at the operator position.
Tecumseh’s Flywheel Brake system provides consumer safety by stopping the engine and blade within three seconds after the operator releases the engine/blade control bail at the handle of the lawnmower. These systems are available on both recoil and electric start models. The engine stopping time is affected by the engine R.P.M. Consult microfiche card #30, the Plus 1 or Parts Smart Look-Up system, or Service Bulletin #107 to determine the correct engine RPM or blade tip speed.
OPERATION 59
BOTTOM SURFACE SYSTEM 59
INSIDE EDGE SYSTEM 60
COMPONENTS 60
Both the Bottom Surface and the Inside Edge systems use the following components:
The brake lever and pad assembly consists of a steel lever with a brake pad bonded to the lever.
The ignition kill switch is a plastic block with a wire extending out of it. The wire is attached to a terminal which is connected to the ignition kill wire. The brake lever contacts and grounds the wire of the switch when the engine / blade control is released, and the ignition module is grounded. This in turn kills the ignition.
The interlock switch is a push button switch that is activated by the brake lever when the engine / blade control is actuated. If there is a starter switch used to start the engine, the interlock switch acts as a safety switch and will not allow the starter to crank unless the engine / blade control is depressed. Where a two motion control is used the interlock switch is utilized as the starter switch.
The Torsion Spring supplies the pressure to the brake lever and brake pad to stop the flywheel.
The Control Cable transfers the motion of the engine / blade control to the brake system.
SERVICE 61
FLYWHEEL REMOVAL 61
BRAKE LEVER AND PAD 61
IGNITION GOUNDOUT TERMINAL 61
STARTER INTERLOCK SWITCH 62
CONTROL CABLE 62
BRAKE BRACKET REPLACEMENT 62
CHAPTER 8 IGNITION 63
GENERAL INFORMATION 63
The ignition systems used on Tecumseh engines are either solid state capacitor discharge modules or magneto ignition systems. The basic functional difference is that the solid state modules are triggered by an electronic switch (SCR). Magneto ignition systems rely on the mechanical action of opening and closing a set of moveable contact points to trigger when the spark will occur.
The solid state ignition system consists of a flywheel magnet and key, charge coil, capacitor, a silicon controlled rectifier, pulse transformer, trigger coil, high tension lead, and a spark plug. Everything except the flywheel magnet, key and the spark plug are located in a encapsulated ignition module. This solid state (CDI - Capacitive Discharge Ignition) module is protected by epoxy filler from exposure to dirt and moisture. This system requires no maintenance other than checks of the high tension lead and spark plug.
The Tecumseh magneto ignition consists of a stator assembly made of laminations, a coil, contact points, condenser, a permanent magnet mounted in the flywheel, high tension lead, and a spark plug. The coil is sealed by epoxy filler, and the points and condenser are sealed from dirt and moisture by a crankshaft seal and cover gasket.
OPERATION 63
SOLID STATE IGNITION SYSTEM (CDI) 63
As the magnets in the flywheel rotate past the charge coil, electrical energy is produced in the module. The energy is stored in the capacitor ( approx. 200 volts) until it is released by an electrical switch (SCR). As the magnet continues to rotate, it travels past a trigger coil where a low voltage signal is produced. This low voltage signal closes the SCR switch, allowing the energy stored in the capacitor to flow to a transformer where the voltage is increased from 200 volts at 200 RPM to 22,000 volts at 3000 RPM. This voltage flows through the high tension lead to the spark plug where it arcs across the electrodes and ignites the air-fuel mixture.
MAGNETO IGNITION SYSTEM (POINTS) 63
As the flywheel turns, the magnets that are mounted in the wheel, pass the coil mounted on the stator. As the magnet's North Pole enters the area of the center leg of the stator, a magnetic field is concentrated through the laminations to the magnet's South Pole. This causes a generation of current flow in the coil's primary winding..
The ignition points are closed.
As the flywheel continues to rotate, the North Pole approaches the last leg of the lamination stack. The magnetic field through the center leg reverses, producing a large change in the magnetic field, and a high current in the primary side of the coil.
At this time, the contacts open and the primary current stops flowing. This change in current causes a voltage in the primary, which induces a high voltage in the secondary winding of the coil. The voltage travels through the spark plug wire, to the spark plug and jumps the gap of the plug to ignite the air/fuel mixture.
IDENTIFICATION OF TECUMSEH IGNITION SYSTEMS 64
COMPONENTS 64
IGNITION TROUBLESHOOTING 66
TESTING PROCEDURE 67
SPARK PLUG SERVICE 68
Spark plugs should be removed, cleaned, and adjusted periodically.
Check the air gap with a spark plug gap gauge and adjust accordingly. Set the spark plug gap at .030" (.762 mm).
Replace the plug if the center and ground electrodes are pitted or burned, or if the porcelain is cracked or discolored.
When reinstalling the plug make sure it is clean of all foreign material.
CONDITIONS CAUSING FREQUENT SPARK PLUG FOULING 68
1. Carburetor setting too rich or air cleaner restricted.
2. Partially closed choke shutter.
3. Poor grade of gasoline.
4. Improper fuel.
5. Restricted exhaust system.
6. Incorrect spark plug.
7. Incorrect spark plug gap.
8. Oil level too high, or breather is restricted.
9. Faulty piston rings.
10. Weak ignition system.
IGNITION TIMING PROCEDURE 68
In order for an engine to run effectively and efficiently, the spark must ignite the compressed air-fuel mixture when the piston is in a specific position to deliver maximum power. This position is known as Before Top Dead Center (BTDC). If the mixture is ignited too soon, kickback can be experienced due to preignition. If the mixture is ignited too late, loss of power can be experienced due to retarded spark.
SERVICE TIPS 71
CHAPTER 9 INTERNAL ENGINE AND CYLINDER 72
GENERAL INFORMATION 72
This chapter covers the cylinder block, piston and rod assemblies, cylinder head, crankshaft, camshaft, valve train, breather, cylinder cover, flywheel, counterbalance systems, and lubrication systems. The governors and the governor systems are covered in Chapter 4.
All Tecumseh engines covered in this manual are four cycle engines with the valves in the engine block. The crankshaft position is designated as either horizontal or vertical as the engine rests on its base. The engines identified by decals or model as XL (Extra Life) or XL/C (Extra Life / Commercial ) are made using aluminum alloy diecast around a cast iron cylinder liner. However, not all engines with cast iron cylinder liners are identified as XL or XL/C. Engine blocks of the heavy frame series (HH, VH) are made of cast iron. All other engines use aluminum alloy for the cylinder block along with pistons that are chromium plated.
OPERATION 72
4-CYCLE ENGINE THEORY 72
All 4-cycle engines require four piston strokes to complete one power cycle. The flywheel on one end of the crankshaft provides the inertia to keep the engine running smoothly between power strokes.
The camshaft gear is twice as large as the mating gear on the crankshaft so as to allow proper engine valve timing for each cycle. The crankshaft makes two revolutions for every camshaft revolution.
1. INTAKE. The intake valve is open and the exhaust valve is closed. The piston is traveling downward creating a low pressure area, drawing the air-fuel mixture from the carburetor into the cylinder area above the piston.
2. COMPRESSION. As the piston reaches Bottom Dead Center (BDC) the intake valve closes. The piston then rises, compressing the air-fuel mixture trapped in the combustion chamber.
3. POWER. During this piston stroke both valves remain closed. As the piston reaches the Before Top Dead Center (BTDC) ignition point, the spark plug fires, igniting the air-fuel mixture. In the time it takes to ignite all the available fuel, the piston has moved to Top Dead Center (TDC) ready to take the full combustive force of the fuel for maximum power during downward piston travel. The expanding gases force the piston down.
4. EXHAUST. The exhaust valve opens. As the piston starts to the top of the cylinder, the exhaust gases are forced out.
After the piston reaches Top Dead Center (TDC), the four stroke process will begin again as the piston moves downward and the intake valve opens.
LUBRICATION SYSTEMS 73
The lubrication system used with all Tecumseh horizontal crankshaft engines covered in this manual utilize a splash type system. An oil dipper on the connecting rod splashes oil in the crankcase to lubricate all internal moving parts. Some engines have the dipper as an integral part of the connecting rod assembly, while others have a dipper that is bolted on with one of the rod bolts.
COUNTERBALANCE SYSTEMS 73
Some Tecumseh engines may be equipped with an UltraBalance® counterbalance system. This system uses a single weighted shaft that is driven off the crankshaft. The shaft's function is to counteract the imbalance caused by the counterweights on the crankshaft and the combustion.
COMPONENTS 74
The cylinder block houses the piston, valves and along with the cylinder cover all the internal components. The block
is a one piece diecast aluminum alloy or cast iron cylinder casting (diag. 10).
The piston transmits the force of the burning and expanding gases through the connecting rod to the crankshaft.
The piston rings provide the seal between the cylinder wall and the piston. The rings keep the combustion pressures
from entering the crankcase and also wipe the oil off the cylinder wall and return it to the sump.
The connecting rod assembly is the link between the piston (piston pin) and the crankshaft.
The cylinder head is a one piece aluminum alloy or cast iron casting that is bolted to the top of the cylinder block. The
many fins provide cooling for the engine.
The crankshaft converts the up and down piston movement to the rotational force (torque) by an offset crankpin or
rod journal.
The camshaft lobes raise and lower the lifters at the proper time to allow air and fuel in and exhaust out of the
cylinder. Teeth on the camshaft gear time the camshaft to the crankshaft.
The valves allow air-fuel mixture to enter the cylinder and exhaust gases to exit. The valves provide a positive seal
when closed.
The valve springs return the valves to the closed position and must be strong enough to maintain valve lifter and cam
lobe contact. The valve retainers lock the spring to the valve stem.
The valve lifters maintain contact on the camshaft and push the valves open.
The crankcase breather is a one way check valve that allows air out and prevents air from coming in. It allows the
engine to develop a partial vacuum in the crankcase during operation.
The cylinder cover (or flange on verticals) provides the bearing surface for the power take off (P.T.O.) end of the
crankshaft and camshaft. This bolted on cover is removed to provide access to all internal components.
The oil pump (vertical shaft only) consists of a steel plunger and a nylon housing that rides on the camshaft eccentric.
The flywheel provides the mass to smooth the effects of one power stroke every other crankshaft revolution. Flywheels
are made of aluminum alloy or cast iron. The flywheel fins act as a fan to cool the engine.
ENGINE OPERATION PROBLEMS TROUBLESHOOTING CHART 75
TESTING 77
ENGINE KNOCKS 77
ENGINE OVERHEATS 77
SURGES OR RUNS UNEVENLY 77
ENGINE MISFIRES 77
ENGINE VIBRATES EXCESSIVELY 78
BREATHER PASSING OIL 78
EXCESSIVE OIL CONSUMPTION 78
LACKS POWER 78
DISASSEMBLY PROCEDURE 79
CYLINDERS 81
CYLINDER HEADS 82
PISTONS, RINGS AND CONNECTING RODS 82
CRANKSHAFTS AND CAMSHAFTS 84
VALVES 85
CRANKCASE BREATHERS 86
CYLINDER COVER, OIL SEAL, AND BEARING SERVICE 87
CRANKSHAFT BEARING SERVICE 88
COUNTERBALANCE SERVICE 89
FLYWHEEL
CHAPTER 10 ENGINE SPECIFICATIONS 90
FOUR CYCLE TORQUE SPECIFICATIONS 91
ENGINE SPECIFICATIONS STANDARD POINT IGNITION 93
SOLID STATE AND EXTERNAL IGNITION 97
CHAPTER 11 EDUCATION MATERIALS AND TOOLS 102
AVAILABLE TECHNICIAN'S HANDBOOKS
692508
Covers the diagnosis and repair of Tecumseh 2-cycle engines. Except the TC Engine and TVS840.
692509
Covers the diagnosis and repair of the Tecumseh 4-cycle light/medium frame engines.
691462A
Covers the diagnosis and repair of Tecumseh 4-cycle large frame engines.
691218
Covers the diagnosis and repair of Peerless® power train components.
694782
Contains technical information for the repair of the TC series, 2-cycle engines.
694988
Contains diagnosis and technical information for the repair of TVS840, HSK/HXL845/850, 2-cycle engines.
695244A
Covers the diagnosis and repair of the OVRM/OVM/OHM/ OHV 4-cycle overhead valve engines.
695578
Covers the diagnosis and repair of the Vector Series, 4-cycle engines.
695185
Electrical Troubleshooting. This video training program will assist the small engine technician in the proper procedures for troubleshooting electrical systems on outdoor power equipment.
695285
An in-depth look at the 800 series transaxles. Detailing the teardown and reassembly procedures for the 800, 801 and 820 transaxles
INSTRUCTIONAL GUIDE
692738
Assists in the use and understanding of the Tecumseh Master Parts Manual. Illustrates time saving features incorporated into the manual. Explains new carburetor parts breakdown format.
4-CYCLE ENGINE FAILURE ANALYSIS
695590
This booklet is designed as a tool for the average technician to correctly assess the cause of failure.
CARBURETOR TROUBLESHOOTING BOOKLET
695907
This booklet is designed as a quick reference to carburetion problems and related repair procedures.
IGNITION SYSTEMS TROUBLESHOOTING BOOKLET
694903
This booklet contains information on the identification, possible problems and related repair procedures of Tecumseh Ignition Systems.
SPECIAL TOOLS BOOKLET
694862
This booklet depicts all specialty tools offered by Tecumseh which can be used on 2 and 4 cycle engines and Peerless units.
QUICK REFERENCE CHART BOOKLET
695933
This booklet contains the quick reference information found on Tecumseh wall charts. This booklet is designed to be used as a work bench quick reference guide when servicing Tecumseh engines and motion drive systems.
TESTER BOOKLETS
694529
Test procedures for Tecumseh electrical components using Graham-Lee Tester 31-SM or 31-SMX-H.
694530
Test procedures for Tecumseh electrical components using Merco-O-Tronic Tester 9800. (Tests are similar for 98, 98A and 79.)
DECIMAL / FRACTION CONVERSIONS
.016 = 1/64
.031 = 1/32
.047 = 3/64
.063 = 1/16
.078 = 5/64
.094 = 3/32
.109 = 7/64
.125 = 1/8
.141 = 9/64
.156 = 5/32
.172 = 11/64
.188 = 3/16
.203 = 13/64
.219 = 7/32
.234 = 15/64
.25 = 1/4
.266 = 17/64
.281 = 9/32
.297 = 19/64
.312 = 5/16
.328 = 21/64
.344 = 11/32
.359 = 23/64
.375 = 3/8
.391 = 25/64
.406 = 13/32
.422 = 27/64
.438 = 7/16
.453 = 29/64
.469 = 15/32
.484 = 31/64
.50 = 1/2
.516 = 33/64
.531 = 17/32
.547 = 35/64
.563 = 9/16
.578 = 37/64
.594 = 19/32
.609 = 39/64
.625 = 5/8
.641 = 41/64
.656 = 21/32
.672 = 43/64
.688 = 11/16
.703 = 45/64
.719 = 23/32
.734 = 47/64
.75 = 3/4
.766 = 49/64
.781 = 25/32
.797 = 51/64
.813 = 13/16
.828 = 53/64
.844 = 27/32
.859 = 55/64
.875 = 7/8
.891 = 57/64
.906 = 29/32
.922 = 59/64
.938 = 15/16
.953 = 61/64
.969 = 31/32
.984 = 63/64
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