Engine Textbook
Engine Textbook
Contents 1 Basic Structure of of an Engine . . . . . . . . . . . . . . . . . . . . . . 1
6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Basic structure of a two-cycle engine . . . . . . . . . . . . . . . . . . . . . . . . 1
1 Spark plug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2 Principles of of Two-cycle Engine Engine Operation Operation . . . . . . . . . . . . 1
2 Cylinder and its elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3 Engine chain saw - Characteristics of vertical engines engines . . . . . . . . . . 25
3 Functions Functions of the Engine Engine Compone Components nts . . . . . . . . . . . . . . . 2
4 Engine oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
1 Fuel ( Gasoline ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
5 Seizure of the cylinder and piston . . . . . . . . . . . . . . . . . . . . . . . . . 26
2 Engine oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
6 Operating principle of the auto-return choke choke . . . . . . . . . . . . . . . . . 26
2-1 Effects of oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
7 Two-cycle engine exhaust gas control . . . . . . . . . . . . . . . . . . . . . . 27
2-2 Viscosity of oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
8 Principle of the new starter starter system, "Karugaru Start ( Quick and Easy Start Start )" . . . . . . . . . . . . . . . . . . . . 28
2-3 Types of engine engine oils and required performance . . . . . . . . . 2 3 Lubricatio Lubricationn mechanism mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3-1 Mixed fuel methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3-2 Mixed gasoline for two-cycle engines engines . . . . . . . . . . . . . . . . 3 3-3 Deterioration of gasoline quality . . . . . . . . . . . . . . . . . . . . 3 4 Air-fuel mixture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4-1 Principle Principle of of the carbure carburetor tor mechani mechanism sm . . . . . . . . . . . . . . . 4 4-2 Types of carburetors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4-3 Fuel-air mixture ratio ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4-4 Operating statuses statuses and mixture ratios ratios . . . . . . . . . . . . . . . . 6 4-5 Role of the choke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 Valve mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5-1 Piston valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5-2 Reed valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6 Ignition system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6-1 Types of ignition systems . . . . . . . . . . . . . . . . . . . . . . . . . 7 6-2 Flywheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6-3 Ignition coil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6-4 Comparison of of ignition system characteristics characteristics . . . . . . . . . . 8 6-5 Spark plug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4 Troubleshooting Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1 Three major elements and inhibitory elements of the normal operation of engines . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2 Troubleshooting and countermeasures countermeasures . . . . . . . . . . . . . . . . . . . . . 10 3 Inspection and cleaning of components components . . . . . . . . . . . . . . . . . . . . . 11
3-1 Inspection of the fuel filter filter . . . . . . . . . . . . . . . . . . . . . . . . 11 3-2 Cleaning of the the air-exhaust port port of the muffler and cylinder . . . . . . . . . . . . . . . . . . . . . . . . . 11 3-3 Cleaning of the the air cleaner . . . . . . . . . . . . . . . . . . . . . . . 11 4 Operation and inspection inspection of the carburetor . . . . . . . . . . . . . . . . . . 12
4-1 Operation of the Walbro WA diaphragm type type carburetor carburetor . . 12 4-2 Operation of the the TK diaphragm . . . . . . . . . . . . . . . . . . . . 16 5 Inspection and adjustment of of the ignition coil . . . . . . . . . . . . . . . . . 20
5-1 Inspection of the ignition coil . . . . . . . . . . . . . . . . . . . . . . 20 5-2 Adjustment of the ignition coil . . . . . . . . . . . . . . . . . . . . . 20 6 Inspection of sparking of the spark plug . . . . . . . . . . . . . . . . . . . . . 21
5 Startup Startup and Storage Storage of of an Engine Engine . . . . . . . . . . . . . . . . . 22 1 Startup procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2 Storage Storage of the engine engine for for a long time time ( more than than one month month ) . . . . 22
1 Basic Structure of an Engine Engines offer a means to produce power regardless of work site locations. For engine-loaded tools categorized as power tools, small and light two-cycle engines are the most appropriate. In this document, we introduce the principles of an engine's operation and structure with a focus on two-cycle engines. The basic structure of a two-cycle engine is illustrated below.
Spark plug
Cylinder Combustion chamber
Choke Carburetor
Air filter
Muffler
Fuel tank
Piston
Scavenging port Needle valve Connecting rod Float Crankshaft Crankcase
2 Principles of Two-cycle Engine Operation
Scavenging
Compression and intake
Compression
Explosion
Exhaust
Explosion Exhaust
Air intake Scavenging
Scavenging
[ One rotation to complete four processes ]
An engine that completes air intake, air compression, air expansion, air exhaust, and air scavenging while the piston makes a single reciprocating motion is called a two-cycle engine. Compression and air intake and air expansion (combustion) and air precompression are performed at the same time in the cylinder and crankcase respectively. 1
3 Functions of the Engine Components Ignition coil
Spark-timing control Spark plug
Air
Air filter
Fuel
( Mixture of gasoline with oil )
Carburetor Produces air-fuel mixture (air-fuel ratio)
1 2 3
Crank chamber Intakes air.
4
Scavenging ( Combustion chamber )
Compression
5
Explosion
Air exhaust
Muffler
6
1. Fuel ( Gasoline ) • Gasoline is made from the distillate fraction of crude oil, in the first stage of crude oil distillation, with a boiling point range of 30 to 200 ºC. Gasoline is divided into premium gasoline of higher octane values and regular gasoline of lower octane values. • For two-cycle engines, regular gasoline (octane value: 89 or higher) is used. Gasoline of a low boiling point is highly combustible. The flammability of gasoline having a high boiling point is low and leaving it as it is over time will allow the combustible contents of gasoline to vaporize and the nonflammable contents to remain.
2. Engine oil 2-1. Effects of oil 1 Lubricating effect :
Oil enters conflicting surfaces between metal parts and supports the load with oil membranes such that the metals do not touch each other directly.
2 Sealing effect :
Oil maintains the gaps between the cylinder, piston, and piston rings sealed to prevent leakage of gas.
3 Cooling effect :
Oil reduces the heat generated on the cylinder, piston, bearing, etc. by thermal propagation effect.
4 Cleaning effect :
Oil washes off carbon, deposit, sludge, etc. generated in the mechanism.
5 Rust-preventive effect : The oil film protects metal surfaces from rust.
2-2. Viscosity of oil Viscosity, or stickiness, is an important property of oil. 1 High viscosity • Strong oil film : Serves as effective lubricating oil. • Low fluidity : Results in a large power loss due to high resistance. 2 Low viscosity • Weak oil film : Has lower lubricating effect. • High fluidity : Has low resistance.
2-3. Types of engine oils and required performance Degree of necessity (compared within a single required performance item :
Required performance
Type of oil
Cleaning effect Dispersibility Acid neutralizing property Oxidative stability Corrosion-resistant and rust preventive property Combustibleness
Wear-resistant and seize-resistant property 2
Gasoline engine oil Two-cycle engine oil Four-cycle engine oil
Diesel engine oil
>
)
3. Lubrication mechanism The lubrication mechanisms of two-cycle gasoline engines are divided into mixed fuel methods in which engine oil is mixed with fuel beforehand and separated lubrication methods in which engine oil and fuel are supplied separately to be mixed subsequently.
3-1. Mixed fuel methods 1 Most two-cycle gasoline engines employ mixed fuel in which engine oil is mixed with fuel beforehand.
Mixed gasoline
2 The typical fuel-to-oil mixture ratio is 25:1. However, oils having a mixture ratio of 50:1 are available in the market as the quality of engine oils have been improved recently. 3 Mixed fuel is atomized by the carburetor and brought into the crankcase. Then, oil adheres to the inner wall and rotating elements in the combustion chamber to serve for lubricating and cooling effects. Finally, the mixed fuel is delivered to the combustion chamber for combustion.
Carburetor
4 Mixed fuel methods have the following advantages and disadvantages. Advantages • The structure is simple without the need for any feeding pump or feeding can. • Fuel feeding is secured even at the start of operation. • Fresh lubricant is always supplied inside the engine. Disadvantages • Oil consumption is large. • Much exhaust smoke and deposit
3-2. Mixed gasoline for two-cycle engines Fuel prepared by mixing gasoline with two-cycle engine oil is called mixed fuel.
20 : 1=5% 25 : 1=4% 33 : 1=3% 50 : 1=2%
Mixture ratio Gasoline: Oil 20 : 1 25 : 1 33 : 1 50 : 1
Oil 1
Gasoline from 20 to 50
3-3. Deterioration of gasoline quality Mixed gasoline, if stored over a long time, may deteriorate due to volatilization, separation, chemical change, or bacterial effect. Bacteria break down gasoline into alcohol and water which cause rust. In addition, the sediment of the dead bodies of bacteria clogs the fuel passage. Volatilization Bacteria Gasoline Oil Water
[Deteriorated gasoline] 3
4. Air-fuel mixture 4-1. Principle of the carburetor mechanism 1 The explosive combustion of fuel to expand the air volume within the cylinder is necessary for the rotation of a gasoline engine. Gasoline is not fed to the cylinder as it is; it has to be atomized for efficient combustion.
[ A ]
[B]
[C]
Venturi tube ( A )
Throttle valve
Nozzle ( B ) Air
2 A carbure tor mixes fuel wit h air by the principle of an atomizer; the atomized fuel is drawn into the engine in accordance with the operating conditions and compressed in the engine. The atomized mixture is gasified. 3 With an atomizer, the pressure at the tip of a narrow stream of strongly pressurized air [ A ] becomes negative ( lower than the atmospheric air pressure ). Due to a difference between the pressure at the liquid level of the nozzle [ B ] and the atmospheric pressure working on the surface [ C ], the liquid is suctioned out of the nozzle and atomized by the flow of the air. 4 The carbu retor ope rates in the manne r that the atmospheric air is suctioned inside the crankcase via the suction passage of the carburetor as the pressure inside the crankcase becomes negative as a result of the rotation of the engine which raises the piston.
Air-fuel mixture
Fuel ( C )
5 At the very moment mentioned above, negative pressure is caused at the narrowest point of the venturi tube ( A ) to make the fuel ( C ) spray out of the nozzle ( B ) for atomization.
4-2. Types of carburetors Carburetors are classified into the float type, diaphragm type, circulation type and other types in accordance with the respective methods of maintaining the fuel in the carburetor ( fuel chamber in the carburetor ) at a fixed level.
• Float type carburetor Suction passage
Needle valve
Float
1 In the case of a float type carburetor, a float is positioned in the fuel to maintain the fluid level fixed and the fuel inflow is adjusted by interlocking the changed fluid level according to the consumption of the fuel with the needle valve.
Fluid level Float arm Float chamber
Drain
• Diaphragm type carburetor High-speed needle
Suction passage Main nozzle
Diaphragm 4
Metering lever
Inlet needle valve
1 In the case of a diaphragm type carburetor, a rubber film called a "diaphragm" is used in place of a float and the fuel is suctioned by the pressure variations in the crank chamber. In this method, the inflow of fuel is controlled on the basis of the pressure difference between the fluid pressure and atmospheric pressure working on both surfaces of the metering diaphragm, with which the needle valve for the control is interlocked.
• Circulation type carburetor 1 The fuel suctioned up by the fuel pump is overflowed from the weir in the chamber to maintain the fluid at a fixed level.
From the fuel pump Weir
2 The structure provides ease of maintenance without the need for any float or needle valve. Caution: Do not incline the engine more than 60 degrees; the fuel flows out of the chamber into the tank to cause fuel deficiency. 3 The internal elements of the chamber are free of corrosion or rust as the carburetor of this type is provided with an auto-drain mechanism, which automatically discharges the fuel in the chamber to the fuel tank by the capillary phenomenon of the drain wire when the engine is stopped.
Chamber
Drain wire
Caution: The time length required from a full-tank state to an empty state in the chamber is about 40 minutes.
Chamber
To the fuel tank
• Flow-rate control Throttle valve methods are available in butterfly type ( butterfly valve type ), piston valve type, or rotary valve type.
[ Butterfly type ]
[ Piston valve type ]
[ Rotary valve type ]
4-3. Fuel-air mixture ratio 1 The mass ratio of fuel to air mixed in the carburetor is called the mixture ratio ( air-fuel ratio ). For complete combustion of fuel, 15 g of air against 1 g of fuel is necessary; this ratio is called the theoretical mixture ratio. 2 A mixture of a ratio lower than the theoretical mixture ratio "1:15" is called a high-density mixture, while a mixture of a ratio higher than the theoretical ratio is called a low-density mixture. A typical mixture range for normal combustion varies from 1:8 to 1:20. 5
4 - 4 . Operating statuses and mixture ratios High Operating status density
Mixture ratio
Low-temperature startup
1:1
Excessive-density combustible mixture Low-speed idling
1:8
Maximum output operation
1 : 13
Theoretical mixture ratio
1 : 15
Economical operation ratio
1 : 16 – 17
2 For example, the mixture ratio 1:13 to secure the maximum output of an engine is called the maximum-output mixture ratio.
1 : 11
Low Extremely-low density density combustible mixture
1 : 20
1 Though the theoretical mixture ratio is required for complete combustion of fuel, the actual mixture ratio required depends on the operating status of the engine in a practical application.
3 An economical operat ing condition with low fuel consumption is achieved at a ratio of 1:16 or 1:17, which is referred to as the economical mixture ratio.
4 A considerably high density, such as 1:1, is required to increase the starting performance for the mixture used for starting up a cold engine.
4-5. Role of the choke It is difficult to supply fuel sufficiently inside the cylinder when it is cold, because the fuel contained in the air-fuel mixture adheres to the inner wall of the cylinder or around the piston in an atomized condition. As a solution to such a problem, a choke is used to reduce the amount of air and increase the amount of fuel for easier startup of the engine under such low temperature conditions.
5. Valve mechanism The cylinder ports and piston in a two-cycle engine serve as the valves in a four-cycle engine. The timing of valve operation is determined by the positions of the ports.
5-1. Piston valve Piston
Air-fuel mixture
Air-intake port
Crankcase
1 An air-intake port, scavenging port, and exhaust port are provided in the inner wall of the cylinder. The ports are respectively opened or closed by the piston. 2 When the piston starts rising from the bottom dead point, the pressure in the crankcase, which is sealed by the piston and oil seal, is reduced gradually. Immediately before the air-intake port is opened by the piston skirt, the pressure reaches the highest negative pressure. 3 The mome nt the air- inta ke port opens, air- fuel mixture starts flowing into the crankcase.
4 This air flow stops when the piston reaches the top dead point. However, when the rpm exceeds 2,000 min-1 in actual engine operating conditions, the air flow continues even if the piston starts descending after the top dead point until the air-intake port starts closing.
5-2. Reed valve Reed
1 An air-intake port is provided in the crankcase wall. A flat spring called a reed valve is attached to the air-intake port. The ree d valve is ope ned or clo sed by the differ ent ial pressure. 2 The reed valve mechanism can prevent blowback at a low rpm, resulting in improved air-intake efficiency.
Air-intake 3 However, it is important to minimize the resistance of the port Crank chamber
6
air flow during air-intake and it is necessary to take into account the durability and oscillation property of the reed valve itself. A reed valve is an effective means against vapor lock.
6. Ignition system 6-1. Types of ignition systems A flywheel magnet consists of an ignition system including a magneto coil and an interrupting device, and a flywheel. The ignition system is either a contact type, CDI or TCI, both of which are non-contact types.
Ignition system Current-interruption type
Capacity-interruption type
Contact type
Non-contact type
Non-contact type
Point type
TCI
CDI
( Old type )
( Transistor Controlled Ignition )
( Capacitor Discharge Ignition )
Ignition coil
Ignition coil
Flywheel Flywheel
6-2. Flywheel A flywheel is provided with a cast magnet for power generation. The flywheel rotates around the fixed coil to cause flux variation in the coil and generate electromotive force. Flywheels are divided into the inner-magnet type and outer-magnet type depending on the position of the cast magnet.
6-3. Ignition coil An ignition coil is a part that generates high voltage electricity used for spark discharge. A primary coil and a secondary coil are separately wound around an iron core. With the current of the primary coil interrupted, high voltage electricity is generated in t he secondary coil by reciprocal induction. The figure on the right shows the cross-sectional view of an ignition coil. The primary coil of about 50 turns, which is a polyurethane conductor wire ( or polyester conductor wire ) having a diameter of about 0.6 mm, is wound around the iron core which consists of layers of silicon steel sheets. The secondary coil of about 4,000 turns, which is a thin wire having a diameter of about 0.06 mm, is wound over the primary coil. The voltage value of the electricity generated as the secondary voltage is determined by the ratio of turns of the primary coil and secondary coil. For example, when the voltage generated on the primary coil is 200 V, the secondary voltage becomes as high as 16,000 V ( 200 V X 4,000 turns/50 turns ).
Primary coil Iron core
Secondary coil
[Ignition coil]
7
6-4. Comparison of ignition system characteristics Ignition system
Ignition signal
Characteristics
• Interruptor ( point ) Point type ( current• Cam interruption type ) • Ignition coil
• ( Trigger coil ) TCI type • Electronic circuit of ( currentthyristor and transistor interruption type ) • Ignition coil
• ( Trigger coil ) CDI type • Electronic circuit of ( capacitythyristor and transistor interruption type ) • Ignition coil
1 The structure is comparatively simple and the price is low. 2 Point-caused problems occur frequently, requiring periodical maintenance. ( Ignition timing is affected due to stain, heat damage, or wear in the point. ) 3 Stable sparking performance is available as the follow-up performance is high during a high speed rotation.
1 The unit ( electronic circuit ) used in place of an interruptor and capacitor is small in size and the number of parts is also limited. 2 Ignition timing does not vary, requiring no adjustment. 3 Ignition characteristic is excellent due to a long secondary discharge time. 4 Stable sparking performance is available as the follow-up performance is high during a high speed rotation.
1 A compact and light type with coils and unit integrated has been developed. 2 Ignition timing does not vary, requiring no adjustment. 3 The secondary voltage is high and the rise of the voltage is very quick, resulting in an excellent ignition characteristic even when the spark plug is stained and excellent acceleration and high-speed operation characteristics.
6-5. Spark plug • Structure 1 The spark plug igni tes the air-fuel mixture by emitting sparks to the air gap by the effect of the high-voltage developed by the ignition coil.
Terminal nut Center electrode
Corrugation
Main metal body
2 When the spark plug is stained or carbon adheres to and is accumulated on the insulating material to lower the insulation resistance, a short-circuit fault is caused and sparking is disabled, resulting in malfunctioning of the engine.
Insulating material
Gasket Fixing screw
Gas volume
Air gap 0.6 — 0.7mm
Lateral electrode
B Screw diameter: 14 mm Standard hex screw subtense size: 20.6 mm Screw diameter
A B C
8
18mm 14mm 10mm
3 A preferable condition of electrode burn includes a thin layer of dry cinder colored light gray, golden brown, or white over the insulating material.
P
M
R
6
L
A
Protrudedinsulation type
Small-size plug ( Bantam type )
With resistance for noise prevention
Thermal value
Screw length: 11.2 mm
Special specification
M Small-size plug P Protruded type R With resistance
2 Burn type Low 4 5 n o t 6 i a i 7 d a R 8 9 10 Cold type High
Screw diameter No indication
L H E
9.5mm 11.2mm 12.7mm 19.0mm
A Special specification S Standard specification V-grooved center Y electrode (excellent ignition characteristic)
4 Troubleshooting 1. Three major elements and inhibitory elements of the normal operation of engines • Gasoline of poor quality • Clogged carburetor jet orifice or the like • Inadequate aperture of adjusting needle • Hardened diaphragm • Clogged tank filter • Clogged tank air vent • Clogged cock or fuel tube • Air leakage • Overheated carburetor (due to vapor lock)
• Clogging between plug electrode • Stained plug • Wet plug • Leakage between high-voltage cable and plug cap • Leakage in primary wire • Plug gap failure • Excessively large gap between flywheel and coil • Dislocated flywheel (without key) • Ignition coil failure • Unit failure
Fuel Proper air-fuel mixture
Spark
“Engine Engine Starts without Fail” Fail
Correct sparks and ignition timing
Pressure No pressure leakage in the combustion chamber and crank chamber
• Worn piston rings • Worn cylinder bore • Stuck piston rings • Cracked oil seal in the crank chamber • Damaged gasket • Seizure of the piston and crank shaft • Clogged muffler • Clogged cylinder exhaust port
9
2. Troubleshooting and countermeasures Condition Starter handle cannot be pulled
Crankshaft does not rotate Crankshaft rotates
Plug is not wet with gasoline even if startup operation is repeated
Cause
Seizure of piston rings Seizure of connection rod bearing Recoil starter failure Fuel tank has no fuel Fuel filter is clogged
Air vent of tank (chamber valve) is faulty
Replacement
Aperture of low-speed fuel adjusting screw is faulty
Adjustment Cleaning Proper activation procedure Cleaning or replacement Inspection and/or replacement Repair or replacement Repair Replacement Repair
Carburetor assembly is clogged with dirt Stained or affected plug Poor connection of a plug cap
No spark
Poor connection or disconnection of high-voltage cable Earthing of high-voltage cable Poor connection or disconnection of ignition coil Poor connection or damage of lead wire
Plug electrodes are short-circuited with foreign matter clogged between them
No compression
Faulty piston rings Worn piston Service life of oil seal in crank chamber has expired Stained or affected plug
Weak sparking
Engine starts but it does not continue idling
Weak compression
Faulty air gap Ignition coil failure Worn piston rings Service life of oil seal in crank chamber has expired Carburetor assembly is clogged with dirt
Strong sparking and Fuel filter is clogged good compression Aperture of low-speed fuel adjusting screw is faulty
Engine stalls Engine starts but acceleration is ...
Acceleration is not smooth or rpm does not rise
Disassembling and parts replacement Fuel replenishment Cleaning or replacement
Improper operation of throttle or pump
Engine does not start
Countermeasure
Idling rpm is too low Carburetor assembly is clogged with dirt Aperture of high-speed fuel adjusting screw is too small Fuel filter is clogged Aperture of high-speed fuel adjusting screw is faulty Muffler is clogged with carbon Air cleaner is clogged Chain brake is set for activation
Removal of foreign matter or overhaul and cleaning of engine if short-circuit occurs frequently Parts replacement Cleaning or replacement Adjustment Replacement Replacement Replacement Cleaning or replacement Adjustment Cleaning Adjustment Cleaning or replacement Adjustment Cleaning Release of brake
Aperture of high-speed fuel adjusting screw is too small Adjustment High-speed fuel passage is clogged with dirt Adjustment Engine starts but ... Fuel consumption is Aperture of high-speed fuel adjusting screw is too large. Adjustment too large Air cleaner is clogged. Cleaning There is no oil in the tank Oil replenishment Oil feeding port is clogged Oil feeding port in the guide bar is clogged Cleaning Chain oil is not discharged Oil filter is clogged Rotation fluctuates at a high speed
Adjustment of chain oil discharge is faulty
10
Adjustment
3. Inspection and cleaning of components 3-1. Inspection of the fuel filter Pull out the fuel filter by using a wire or the like through the fuel filler port and wash the filter with gasoline, by rubbing it with fingers as necessary. After cleaning, remove the fuel filter and blow it with your breath to see whether air passes through it. Replace the filter with a new one if the air does not pass through it.
Fuel filter
3-2. Cleaning of the air-exhaust port of the muffler and cylinder To clean the muffler, insert a screwdriver or the like into the muffler air-exhaust port or heat the muffler with a burner to burn off the carbon in the muffler. To clean the air-exhaust port of the cylinder, remove the muffler, block the air-exhaust port with the piston so that the carbon in the air exhaust port does not enter the cylinder, and then scrape off the carbon with a screwdriver or the like. Caution : Be careful not to damage the piston. Spark plug
Air-intake port
Screwdriver
Block the air-intake port with the piston.
3 - 3 . Cleaning of the air cleaner Remove the air cleaner cover assembly and brush off the chips and dust from the air filter, seal, and air cleaner cover assembly. If the air filter is stained excessively, wash the air filter with gasoline. Make sure to dry the filter before use.
Cleaner cover
Air filter cover
Air Filter
11
4.Operation and inspection of the carburetor 4-1. Operation of the Walbro WA diaphragm type carburetor Engine side
Air cleaner side Engine impulses activate the pump diaphragm for the suction of fuel.
Crank chamber
Fuel flows in through the main nozzle at high speeds.
Fuel tank
The amount of air and air speed are changed by the aperture of the throttle valve, to change the inlet flow of fuel.
Inlet valve
Fuel flows into from the idle port at low speeds.
It is necessary to maintain the fluid level fixed for flow of a fixed amount of fuel into the engine according to the aperture of the throttle valve. The same amount of fuel as that flows out of the fuel chamber is taken by the function of both the metering diaphragm and inlet valve, resulting in a fixed amount of fuel in the carburetor.
Idle port
• Idling aperture Low-speed fuel adjusting screw
• Intermediate aperture Pump diaphragm
Venturi tube
Throttle valve
High-speed fuel adjusting screw
Main nozzle
Idle port
Metering diaphragm
1 The th rott le va lve is part ia lly open. As the air speed near the throttle valve is faster than that in the venturi tube, the resultant negative pressure causes the fuel to be ejected out of the idle port.
12
• Full aperture
2 The pressure nea r the ven tur i tube becomes negative as the rpm increases with increasing aperture of the throttle valve and the fuel starts to flow in from the main nozzle partially.
3 Th e ai r spee d in th e ve nt ur i tube is maximized as the aperture of the throttle valve is fully opened and the fuel mainly flows in through the main nozzle. The idle port also ejects the fuel as the negative pressure near the venturi tube also helps.
4-1-1. Inspection points
Completely fastened? Adjusted correctly? (See pgs. 15 and 16.)
No damage, looseness, or hardening?
No damage or leakage?
(See p. 20)
Positioned correctly without deformation?
Valve is worn or clogged with dirt?
Overflow. No fuel flows out.
rpm of the engine is abnormal. Startup is difficult.
Clogged with dirt?
Adjusted correctly? (See pgs. 15 and 16.)
Insufficient acceleration. Unstable at low speeds. Unstable at high speeds.
No damage, looseness, or hardening?
No damage or leakage?
• Fuel does not flow in. • rpm of the engine is abnormal. • Engine startup is difficult.
Completely fastened
13
4-1-2. Inspection procedure 1 When washing the body, use gasoline or t he like for washing and blow it with air after washing. 2 Check the main jet for adhered dirt or corrosion. Wash the jet, if dirt is detected, and blow it with air after washing. Replace the jet with a new one if corrosion is detected. 3 Inspect the gasket and the like for deformation or damage. Replace them with new ones if they are deformed or damaged. 4 Inspect the pump diaphragm for hardening or damage. Check the inlet valve and outlet valve to make sure they are flat, free from bends. 5 Inspect the metering diaphragm to make sure it is free from hardening, damage, or bends in the plate. 6 Inspect the pump body after washing, for deformation in the metering lever and spring, faulty lever height, dirt in the inlet screen, malfunction of the valve, or leakage in the valve. To check the valve for normal operation, blow the check valve in the pump body with your breath, with the use of rubber or vinyl pipe or the like. If the valve stops when you blow the air and the valve opens when you suck the air, the check valve function is in good order. ( Caution: Do not blow the check valve with high-pressure air. )
4-1-3. Adjustment of carburetor Operate the following three types of s crews for the adjustment of the carburetor.
d o h t e m g n i t s u j d A
d r a d n a t S
Idling adjusting screw
High-speed fuel adjusting screw
Low-speed fuel adjusting screw
Air volume during idling is adjusted. Rotating the screw ( the stopper on the throttle valve close side ) clockwise increases the engine rpm, while rotating it counterclockwise decreases the engine rpm.
Fuel flow rate during high-speed operation is adjusted. Rotating the screw clockwise reduces the fuel flow rate ( thin fuel ), while rotating it counterclockwise increases the fuel flow rate ( thick fuel ).
Fuel flow rate during low-speed operation ( idling ) is adjusted. Rotating the screw clockwise reduces the fuel flow rate ( thin fuel ), while rotating it counterclockwise increases the fuel flow rate ( thick fuel ).
2,700 to 3,500 min -1 (Make sure that the blade does not rotate.)
Rotate the screw backward 1 and 1/8 turns from the fully-closed position ( 1 to 1 and 1/2 turns depending on the model ).
Rotate the screw backward 1 and 1/8 turns from the fully-closed position ( 1 to 1 and 1/2 turns depending on the model ).
The procedure to "rotate the screw backward 1 and 1/8 turns from the fully-closed position" in the standard setting for the high-speed fuel adjusting screw and low-speed fuel adjusting screw refers to a position of each screw which is to be reached finally for the setting by rotating the screw backward 1 and 1/8 turns from the extreme position reached first by rotating the adjusting screw clockwise slowly.
Idling adjusting screw (T) High-speed fuel adjusting screw (H)
Low-speed fuel adjusting screw (L)
14
4-1-4. Fine adjustment Generally speaking, the optimum adjusted position of an engine carburetor varies with the temperature and idling conditions. Carry out fine adjustment of the carburetor in accordance with the following procedure if each standard setting does not result in satisfactory engine performance. When the high-speed fuel adjusting screw or low-speed fuel adjusting screw is rotated with the engine activated, the rpm of the engine varies as shown in the figure on the right. In short, rotating a fuel adjusting screw clockwise or counterclockwise, with the throttle aperture fixed, finds a certain position where the engine rpm becomes the highest level.
Position of the screw for Setting the highest engine rpm position E n g i n e r p m
Too thin
Too thick
A. Idling adjustment 1 The rpm is adjusted with the idling adjusting screw so that the engine can rotate steadily without the rotation of the blade. If the rpm is not obtained, standard setting with the low-speed fuel adjusting screw shall be performed.
1/8 to 1/4 turns Counterclockwise
Clockwise
Fuel adjusting screw
2 The position at which the engine reaches the highest rpm shall be determined by rotating the low-speed fuel adjusting screw clockwise or counterclockwise. 3 The set positi on shall be at a position reache d by rotating the low-speed fuel adjusting screw counterclockwise by 1/8 to 1/4 turns from the position determined in the step 2 above ( the engine rpm is reduced by 200 to 300 min-1 as a result ). 4 Operate the idling adjusting screw so that the idling rpm reaches 2,700 to 3,500 min-1. B. High-speed adjustment Rotate the high-speed adjusting screw, in the same manner as with the low-speed adjusting screw, clockwise or counterclockwise to find a position where the engine reaches the highest rpm. The set position shall be at a position reached by rotating the high-speed fuel adjusting screw counterclockwise by 1/8 to 1/4 turns from the position determined above. If the highest rpm does not result from this procedure, use the standard setting. Fuel that is too thin may cause seizure and fuel that is too thick may cause carbon clogging. ( The setting is usually made for the same effect as with the low-speed fuel adjusting screw. ) C. Height of metering lever 1 Bend the metering lever in the carburetor slightly so that the height of the metering level is 1.65 mm as shown in the figure on the right. The height varies with the model.
Metering lever 1.65mm
Carburetor body
Clever suggestion Operate the low-speed fuel adjustment first and return the high-speed fuel adjusting screw to the same position obtained by the low-speed fuel adjustment ( by the same number of screw turns ) for quick adjustment.
15
4-2. Operation of the TK diaphragm
Primer pump
1 Pressing the primer pump repeatedly causes the pressure inside the metering chamber to become negative and turns the diaphragm upward. As a result of this, the needle valve opens to suction the fuel from the fuel tank. 2 After the metering chamber is filled with the fuel, the fuel is discharged out of the return port to return to the fuel tank. Finish the primer pump operation after confirming the completion of this particular circulation cycle of fuel. 3 While the primer pump is operated, the check valve is closed by the negative pressure; thus preventing the air from being suctioned from the nozzle. 4 When the engine is cold, close the choke valve and pull the recoil starter so that more fuel than usual is introduced via the needle jet as the negative pressure of engine increases for suction. This is done to realize a thick mixture suitable for startup of the engine. Open the choke valve after the engine starts.
Check valve Metering chamber
Fuel tank
Choke valve
5 Once the engine is started and warmed up, restarting the engine can be made without closing the choke valve. However, operate the priming procedure once again when the fuel is completely consumed. 6 For idling aperture, the aperture of the throttle valve must be adjusted by operating the idling adjusting screw. The fuel flow rate is controlled by the gap between the needle jet and jet needle.
Air
7 The idling negative pressure adjusting groove provided at the bottom of the throttle valve can optimize the negative pressure that works on the fuel injection hole, thus smoothing the fuel flow during idling operation. 8 In the case of intermediate aperture, the fuel flow rate is controlled by the gap between the needle jet and jet needle.
Metering chamber
9 In the case of full aperture, the fuel flow rate is mainly controlled by the needle jet, with the main adjusting screw used for adjustment.
Idling negative pressure adjusting groove Throttle valve
Needle jet
Jet needle
Idling aperture 16
Intermediate aperture
Full aperture
4 - 2 - 1. Inspection points
Idling adjusting screw Inspect it to make sure it is adjusted properly. Low-speed rpm: 2,700 to 3,500 min -1
E-ring
Jet needle
Inspect it for deformation and make sure it is adjusted properly.
Replace it with a new one if found worn. If verdigris has adhered to it, clean it as well as the needle jet.
Gasket Carburetor body Inspect the fuel passage for clogging with dirt, corrosion, or wear. Clean or repair it as necessary.
Metering lever spring
Inspect it for damage or leakage. Pump diaphragm Inspect it for damage, hardening, or warpage. Pay attention to the correct assembling order of the parts
Pump gasket Inspect it for damage or leakage.
Main adjusting screw Inspect it for wear and make sure it is adjusted properly. High-speed rpm: 10,500 to 11,000 min -1
Pump cover Inspect the fuel passage for clogging with dirt or damage.
Metering lever spring Inspect it for deformation and make sure it is positioned in place.
Needle valve
Gasket
Inspect it for wear or dirt. Air tightness test Valve-opening pressure: 0.14 Mpa Valve-closing pressure: 0.049 Mpa or more
Inspect it for damage or leakage.
Metering lever Inspect it to make sure it is adjusted properly. Lever height: 2.1 to 2.4 mm from the bottom of the carburetor body
Priming pump Inspect it for cracks, damage, or leakage.
Diaphragm gasket Inspect it for damage or leakage.
Metering diaphragm Inspect it for damage, hardening, or warpage. Replace it with a new one if found defective.
Combination valve Metering lever pin
Inspect it for clogging with dirt or warpage.
Check valve Inspect it for damage, hardening, or warpage.
17
4-2-2. Adjustment of the carburetor assembly 1 Adjustment of idling rpm Operate the adjusting screw to adjust the idling rpm. • Rotating the screw clockwise increases the rpm. • Rotating the screw counterclockwise decreases the rpm. If the cutting blade rotates in idling mode, decrease the rpm so that the blade does not rotate. If the rpm is too low in idling mode, the engine may stop. If that happens, increase the rpm by making sure that the cutting blade does not rotate.
Adjusting screw
Main adjusting screw
2 Adjustment of low-speed and intermediate-speed rpm The low-spe ed and intermedi ate-speed rpm is determined by the position of the jet needle clip. 3 Adjustment of high-speed rpm The high-speed rpm is adjusted by operating the main adjusting screw. • Rotating the screw clockwise reduces the flow rate ( thin mixture ). ( The engine rpm increases normally. ) • Rotating the screw counterclockwise increases the flow rate ( thick mixture ). ( The engine rpm decreases normally. ) Basically, use the standard setting. When adjusting the rpm under unavoidable circumstances, rotate the main adjusting screw clockwise or counterclockwise with the cutting blade in place. After finding a position where the rpm becomes the highest, rotate the screw backward by 1/8 turns counterclockwise. 4 Standard setting of the carburetor assembly is completed as described below.
Adjusting screw
2,700 to 3,500 min-1 ( Make sure that the blade does not rotate. )
Position of jet needle clip
Middle of the three positions
Main adjusting screw
1 and 3/4±1/2 turns backward from fully-closed
The standard setting of the main adjusting screw is completed by rotating the screw clockwise slowly to its extreme end and then returning the screw counterclockwise. 5 The jet needle of the throttle valve is fixed in position with an E-ring. Changing the position of the E-ring varies the gap between the jet needle and needle jet; thus changing the fuel flow rate and adjusting the air-fuel ratio. • Attaching the E-ring to the upper groove of the clip reduces the flow rate ( thin mixture ). Standard position of the clip (middle level) • Attaching the E-ring to the lower groove of the clip Fuel is thinner. increases the flow rate ( thick mixture ). 6 When the jet needle is worn to result in an excessive amount of fuel after using the equipment for a long time or if the fuel consumption is excessive by the use in a cold region, change the position of the clip for adjustment.
E-ring Fuel is thicker.
Jet needle
18
7 Inspection of the inlet valve A
Stepped wear
1 Remove the dirt around the needle valve. Replace the valve with a new one when the tapered top of the needle valve has worn with a step of about 0.5 mm or more. 2 Since the mounting load of the metering lever spring (B) is important, be careful not to expand the spring or change the free length. 3 Make sure that the spring is securely seated over the convex section of the metering lever.
B
Dirt
8 The standard height of the control lever is 2.1 to 2.4 mm from the surface of the packing. The level is satisfactory as long as the lever is flush with the plate surface. Adjust the control lever height, checking with a rule or other similar tool.
Control lever 2.1 to 2.4 mm Packing surface
Control lever
Plate
Plate
19
5. Inspection and adjustment of the ignition coil 5-1. Inspection of the ignition coil • Inspect the ignition coil for coil disconnection and layer short with a tester.
Inspection of the primary coil
Inspection of the secondary coil
Resistance of the secondary coil K Ω
Model
Resistance of the secondary coil K Ω
CS35EC
1.2 — 1.8 ( CDI )
CG24E
1.3 — 1.8 ( CDI )
CS35ED
1.2 — 1.8 ( CDI )
CG22ED
1.5 — 2.5 ( CDI )
CS40ED
1.2 — 1.8 ( CDI )
CG24ED
1.3 — 1.8 ( CDI )
CS35EC2 (S)
1.2 — 1.8 ( CDI )
CG26ED
12 — 13 ( TCI )
CS35ED2 (S)
1.5 — 2.5 ( CDI )
CG26EF
12 — 13 ( TCI )
CS35ED2
1.5 — 2.5 ( CDI )
FCG21E
1.5 — 2.5 ( CDI )
CS40ED2
1.5 — 2.5 ( CDI )
FCG23E
1.3 — 1.8 ( CDI )
CS40EF
1.5 — 2.5 ( CDI )
FCG25E
12 — 13 ( TCI )
CS45EF
1.5 — 2.5 ( CDI )
E12
10 ± 20% ( TCI )
E20SA
10 ± 20% ( TCI )
E26SA
10 ± 20% ( TCI )
Model
5-2. Adjustment of the ignition coil Adjustment of the gap between the periphery of the magneto rotor and the ignition coil 1 Loosen the hexagon socket head screw in the manner that the ignition coil is fastened temporarily.
Ignition coil Hexagon socket head screw
2 Adjust the gap between the periphery of the magneto rotor and ignition coil in a range of 0.3 to 0.4 mm.
Gap 0.3 to 0.4 mm
3 With the gap as set above, fasten the hexagon socket head screw finally. Magneto rotor
20
6. Inspection of sparking of the spark plug Caution : • Do not touch the metal part of the spark plug when pulling the starter handle. Otherwise an electric shock may be caused. • Wipe off the fuel adhered to parts near the spark plug to prevent them from catching fire. (1) Remove the spark plug off t he cylinder. If carbon has adhered to the e lectrode of the spark plug ( forming bridges ), clean the electrode with a brush. If the electrode gap is faulty, adjust it to a specified dimension. If the electrode is wet with fuel, wipe it off with a cloth. Then, remove the fuel remaining in the cylinder by the procedure mentioned below. 1 Remove the spark plug off the cylinder. 2 Open the choke (with the choke pressed down) . 3 Open the throttle (pulled condition) . 4 Pull the starter handle several times to remove fuel completely.
Electrode gap ( 0.6 to 0.7 mm )
Electrode
Spark plug
(2) Insert the spark plug in the plug cap and make the electrode touch the metal part of the engine. Then, turn the switch to "ON" and pull the starter handle lightly. High-voltage wire
(3) If the setting is in good condition, the spark plug electrode will spark with a pop.
Spark plug cap Spark plug Ignition spark
Engine metal part
[ Defective conditions ]
0.8mm 0.6mm
Smoldering
Flashover
Expanded gap due to friction
Bridge
21
5 Startup and Storage of an Engine 1. Startup procedure 1 Startup procedure : Chain saw A. When the engine is cold 1 Set the chain brake, if any provided. 2 Turn the switch to "ON" (Start). 3 Pull the choke lever ( to close the air passage ). 4 Set the throttle lever to the "half-open" state. 5 Press the primer pump, if provided, several times and confirm that the fuel has entered the primer pump. 6 Pull the starter handle several times. 7 When there is an explosion sound, push in the choke lever (to open the air passage). 8 Pull the starter handle again. 9 Pull once and release the throttle lever to start idling. 0 Release the chain brake. B. When the engine is warmed up 1 Turn the switch to "ON" ( Start ). 2 Pull the starter handle. Caution : If the engine does not start after pulling the starter handle ten times, remove the spark plug and remove the fuel from inside of the cylinder and the spark plug. Then, perform the procedure A above.
2 Startup procedure : Weed cutter A. When the engine is cold 1 Turn the switch to "ON" ( Start ). 2 Press the primer pump, if provided, several times and confirm that the fuel has entered the primer pump. 3 Set the choke lever to "CLOSE". 4 Pull the starter handle several times. 5 With the engine started, adjust the choke lever gradually toward "OPEN." If the engine starts once and stops immediately, open the choke lever and pull the starter handle again to start it again. B. When the engine is warmed up 1 Turn the switch to "ON" ( Start ). 2 Press the primer pump, if provided, several times and confirm that the fuel has entered the primer pump. 3 Pull the starter handle. * Be careful not to cause excessive fuel intake.
2. Storage of the engine for a long time ( more than one month ) 1 Drain the fuel tank completely. 2 In the case of an engine with a primer pump, remove the fuel from the carburetor fuel chamber by the primer pump. 3 Start the engine to consume the fuel in the carburetor passage completely. 4 Remove the spark plug and supply a few drops of two-cycle engine oil through the plug mount hole. Then, pull the starter several times so that oil film is formed over the surfaces of the piston and cylinder wall (rust prevention measure). 5 Set the piston at a level about 10 to 15 mm below the top dead point. (This is to prevent insects from entering via this air-intake port or air-exhaust port.) 6 Attach the spark plug in place and put the engine in a dry and well-ventilated location.
22
6 References 1. Spark plug • Plug with a resistor element
Resistor element
A plug with a resistor element ( R plug ) refers to a spark plug that has a built-in resistor with resistance of about 5 k Ω for the prevention of radio noise. When a plug sparks, radio noise develops as the ignition system undergoes a very rapid change in current. Employing a resistor in a spark plug can suppress such a rapid change in current in the ignition system to alleviate the change in current for the reduction of radio disturbance. Features : 1 The plug eliminates ignition noises that can affect AM/FM radio and television performance. 2 Th e se rv ic e ar ea of mo bi le ha m, bu si ne ss ra di o, or personal radio can be expanded.
Cross-sectional view
3 The plug can prevent the malfunction of electronic control for engine generators.
• Green plug A gre en plug is provided wit h a V-groo ve on the center electrode. Features :
90-degree V-groove at the tip of the center electrode
Flame kernel (source of spark) Anti-inflammatory action by the center electrode is minimized for the machined 90-degree Vgroove.
Center electrode
Outer electrode
1 The V-groove is in parallel with the center electrode to eject sparks outward with respect to the electrode without fail. Since the flame kernel ( source of spark ) is formed in an outer position where anti-inflammatory action ( action of the electrode to deprive the source of spark of heat ) rarely takes place, the ignition characteristic improves. 2 With the ignition characteristic improved, the starting performance, acceleration efficiency, idling stability, and fuel performance are effectively increased. 3 With a V-groove machine in the center electrode, the tip of the center electrode is sharply pointed for increased sparking performance.
The flame kernel (source of spark) is enlarged outward as the anti-inflammatory action is limited.
• Spark plug interchangeability CHAMPION
NGK
DENSO
L86C
B6HS
W20FS
Standard type
CJ8
BM6A
W20M
Insulator-discharging type
CJ8Y
BPM6A
W20MP-U
Insulator-discharging type
CJ7Y
BPM7A
W22MP-U
Plug with resistor
RCJ8Y
BPMR6A
W20MPR-U
—
BPM7Y
—
Green plug
23
2. Cylinder and its elements • Bore and stroke
Top dead point
Stroke
Bore
1 The inner diameter of the cylinder is called a bore, while the piston motion distance is called a stroke. Generally, a short-stroke engine refers to an engine whose bore is larger than the stroke and is suitable for high rpm applications.
Bottom dead point
• Total volumetric displacement ( total piston displacement ) Top dead point VC
L
V
1 Volumetric displacement ( piston displacement ) refers to the volume of air suctioned or exhausted by a single stroke of the piston inside the cylinder. This volumetric displacement value is a typical measure to represent the size of an engine. 2 The volumetr ic displacement is equal to the volume of intake air and is closely associated with the output of the engine resulted from the combustion and expansion of air.
Bottom dead point
3 The volumetric displacement is generally expressed in mL and determined by the following equation. V : Total volumetric displacement (mL)
V=
π
4
D2LN
D : Cylinder bore (cm) L : Piston stroke (cm) N : Number of cylinders π
: 3.14
• Compression ratio Top dead point VC
V
L Bottom dead point
1 A compression ratio indicates the degree of compaction of the intake air. It is the ratio of the upper volume of a cylinder ( cylinder volume plus combustion chamber volume ) when the piston is at the bottom dead point against the volume left at the top of the cylinder when the piston is at the top dead point ( combustion chamber volume ). 2 Typical compr ession rati os of engines are 6 to 8 for two-cycle engines, 8 to 11 for four-cycle engines, and 16 to 20 for diesel engines.
Compression ratio =
24
Cylinder volume ( V ) + Combustion chamber volume ( VC ) Combustion chamber volume ( VC )
3. Engine chain saw -- Characteristics of vertical engines 1. Excellent high-speed performance 1 A short-stroke engine is used for the vertical engine structure so that the product height can be minimized. 2 A short stroke engine can reduce the piston speed in comparison with other types of engines having the same displacement and engine rpm. 3 The engine performance is suitable for high-speed rotation due to reduced sliding load with the piston. 4 The engine fits well with an application such as a chain saw which involves full-open operation. 5 "Excellent high-speed performance" implies that the engine is suitable for full-open operation, not that its full-open rpm is high.
2. Excellent durability 1 The engine employs a suction-thrust structure in which the piston is pressed against the air-intake side when the piston moves downward from the top dead point. 2 The air-intake side of the piston where the temperature is lowest in the cylinder serves as the sliding surface in this structure; therefore, durability against seizure is increased. A horizontal engine employs an exhaust and scavenging-thrust structure in which the piston is pressed against the exhaust and scavenging side ( high in temperature ). 3 With the piston speed reduced, durability against seizure is increased.
3. Low pitch sound ( tone quality is also low ) 1 With the piston speed reduced, the tone is low. 2 Since the muffler can be large in size, the noise reduction effect can be increased. A muffler can be installed in a front position; the long muffler with large capacity can be employed.
4. Low risk of a burn injury 1 The muffler is located at the front and farthest point from the operator; thus reducing the risk of a burn injury.
4. Engine oil • Role of engine oil Engine oil is indispensable as it lubricates the major rotating elements of the engine such as the piston, piston rings, and crank shaft.
Friction-reducing effect
Sealing effect
Cooling effect
Cleaning effect
• Instruction related with engine oil There are a great variety of two-cycle engine oils in the market. Select engine oil carefully and heedfully since some of these oils are not recommendable in terms of performance as a lubricant. 25
• Classification according to the Fire Service Law Type Type IV
Product name
Flash point
Equivalent oil type
Designated regulation volume
Class 1 oil product
Lower than 21ºC
Crude oil, gasoline, and naphtha
200L
Class 2 oil product
21 to 70ºC
Kerosene and diesel oil
1,000L
Class 3 oil product
Higher than 70ºC
Heavy oil and lubricant
2,000L
Designated regulation volume: In accordance with Articles 30 and 9-3 of Chapter 4, Section 1 “Standards for Storage and Handling of Hazardous Substances of Amounts Lower Than the Designated Regulation Volume” under the Fire Prevention Ordinance General Standards, handling and storage of hazardous substances of amounts lower than the regulation volume stipulated under the government decrees concerning the regulation of hazardous substances (referred to as “Designated regulation volume” hereinafter) must comply with the technical standards specified independently.
5. Seizure of the cylinder and piston Seizure of the cylinder and piston is often attributed to careless or improper handling of the users. Typical causes of seizure are described below. Examples of causes of seizure of the cylinder and piston 1 Raw gasoline or gasoline of low mixture rates was used. 2 High-speed continuous operation with a fully opened throttle was carried out. 3 Oil of poor quality was used ( old and deteriorated gasoline mixture ). 4 A lot of foreign matter was suctioned via the air cleaner ( such as sand and/or dust ).
6. Operating principle of the auto-return choke 1 If you pull the choke knob under the initial condition illustrated below,
2 the choke will close and the throttle will be half-opened.
Throttle: Idling
Throttle: Half-opened
Choke: Open
(Engine rpm: 7,000 — 7,500min-1 )
3 Press in the choke knob when you hear the first explosion sound. Throttle: Remains half-opened
Choke: Open Choke: Closed
Choke knob
Press the decompression knob to activate the brake. Then, pull the recoil rope.
With only the choke opened and the throttle half-opened, press the decompression knob to start the engine. Hold the throttle trigger to release it. The engine returns to the idling condition shown in the figure1.
26
7. Two-cycle engine exhaust gas control • Toxicity of engine exhaust gas components Carbon monoxide ( CO ), nitrogen oxide ( NOx ), and hydrocarbon ( HC ), which are regulated by CARB and EPA, are harmful to humans in particular. Substance name
Effects on the human body
Major sources of atmospheric contamination
CO
It easily combines with hemoglobin in blood to cause anoxia that hinders circulation of oxygen all through the human body, which then causes headache and/or dizziness, leading to death in the worst case scenario.
Typical sources include automobiles, especially during idling of engines. It is a major product of the incomplete combustion of carbon and carbon-containing compounds.
NOx
NO becomes NO2 through photochemical reactions and causes asthma when the density is low. It affects human lungs, when the density is high, and sometimes leads to death. Coexistence of NO with HC is the cause of photochemical smog, causing serious breathing problems.
Typical sources include automobile exhaust gas, gases generated from chemical factories, gases exhausted from types of incineration facilities. It is produced either through the oxidation of nitrogen in the atmosphere during combustion of substances or through the oxidation of nitrogen oxide in the process of combustion.
HC
HC by itself has no toxicity; however, the coexistence of HC with NOx causes photochemical smog, which hinder vision and stimulates mucous membranes of eye. It is a typical product through the oxidation of NOx during combustion.
Typical sources include automobile exhaust gas and gases generated from types of incineration facilities. With two-cycle engines, the unburned gas after the blowing out of fresh air in scavenging step is the source of this substance.
• Exhaust gas regulation (Emission: 20 to 50 cc, handheld) Year Regulation
CARB (USA) (State of California only)
EPA (USA) (All states except for the State of California)
EC (EU member nations)
Japan: Voluntary regulation (Japan Land Engine Manufacturers Association)
Total volume control
Total volume control
Individual regulation
Total volume control
95
96
97
98
Tier 1 THC + Nox : 246 CO : 805
99
00
01
02
03
04
05
(g/kW•h) 06
07
Tier 2 THC + Nox : 72 CO : 536, PM : 2
08
09
10
11
12
13
14
Tier 3 THC + Nox : 50 CO : 536, PM : 2 Transpiration control 2g/m2 /day
Phase 1 THC + Nox : 246 CO : 805
Stepped regulation
THC + Nox : 246 50 CO : 805
Stage 1 THC + Nox : 246 CO : 805
Phase 2 THC + Nox : 50 CO : 805
From February 2008
Primary phase THC + Nox : 246 CO : 805
Stage 2 THC + Nox : 50 CO : 805
Secondary phase THC + Nox : 50 CO : 805
THC NOx CO PM
: Total hydrocarbon : Nitrogen oxide : Carbon monoxide : Particulate matter 27
8. Principle of the new starter system, "Karugaru Start ( Quick and Easy Start )" • When the rope reel rotates with the starter handle pulled, the complete spring rotates via the ratchet. • When the complete spring rotates, the cam plate connected with the startup spring housed in the complete spring rotates. The torque is transmitted to the crank shaft as the cam plate is engaged with the starter pulley. • Since the compressive force of the cylinder is large, the crank shaft does not rotate. Only the startup spring is rotated to accumulate the force. • With the starter handle returned in place, the rope reel is wound back by the spiral spring. However, the complete spring is not wound back by ratchet B; the force in the startup spring remains unchanged. • Then, with the starter handle pulled again, the startup spring is wound back further to increase the accumulated force. When this force becomes larger than the compressive force of the cylinder, the accumulated force in the startup spring is released all at once, to finally rotate the crank shaft and start the engine operation.
Compressive force
Starter housing
1
Starter handle
Spiral spring Crank shaft Rope reel Complete spring Ratchet Ratchet B Startup spring
Cam plate
2
Starter pulley
3 4 * The arrows in the figure show the respective directions of rotation and activation order
28
5 6
Crank shaft
