Difference between revisions of "Group 29 - 5 HP IC Motor"

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(Disassembly Process)
(After Assembly)
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==After Assembly==
 
==After Assembly==
  
Engine Operation
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===Engine Operation===
  
 
This engine was designed as a small 4-stroke engine, which was most likely used to power a push mower. The operation of this product begins initially with the startup. This is done when the operator presses the primer bulb a few times, which causes gas to be forced into the carburetor and also removing any air in the fuel line. The operator then proceeds to manually pull the draw string, which is indirectly attached to the crankshaft by a clutch mechanism. When the clutch is engaged during startup, the crankshaft is forced to rotate, initiating the four stroke cycle. This means that there are four necessary steps or strokes needed to complete a cycle. These four strokes are the intake, compression, power and exhaust. The process begins when air is drawn through the air filter, where it then travels through the intake tube into the carburetor. When the air reaches the carburetor, gas is released through small jets, causing atomization to guarantee a saturated mixture of air and fuel. This mixture is regulated by the carburetor which is dependent upon the users desired operation speed. This is done by using a throttle valve to control the air flow. The mixture is then drawn into the engine through the intake valve during the intake stroke. The intake valve is controlled by the camshaft, which is driven by the crankshaft. The valve opens during the intake stroke, which starts with the piston at top dead center (TDC), meaning that the piston is at a position that is the farthest away from the crankshaft. The piston then starts traveling towards the crankshaft drawing the air-fuel mixture into the combustion chamber. When the piston reaches bottom dead center (BDC), meaning that the piston is at its closest position to the crankshaft, the intake valve closes. This is then the beginning of the compression stroke, during which the piston returns to TDC. The fuel-air mixture is compressed during this stroke to raise its temperature closer to its ignition point. When the piston reaches TDC for the second time, the power stroke is initiated. The piston then begins its return to BDC, when just passed TDC, a spark is generated from the spark plug. Spark is generated by a permanent magnet on the flywheel that rotates past a pickup coil. The spark then causes the mixture to combust, causing it to vaporize. The burning of the gas results in an increase of temperature, which causes the gas to expand. The expansion increases the pressure in the combustion chamber, which forces the piston back toward the crankshaft. When the piston reaches BDC for the second time it begins the exhaust stroke. The piston is then driven back towards TDC due to the rotational momentum of the crankshaft. As the piston returns to TDC the exhaust valve opens allowing the remaining gases to be forced out of the chamber. As the piston reaches TDC, the exhaust valve closes and the cycle repeats itself.
 
This engine was designed as a small 4-stroke engine, which was most likely used to power a push mower. The operation of this product begins initially with the startup. This is done when the operator presses the primer bulb a few times, which causes gas to be forced into the carburetor and also removing any air in the fuel line. The operator then proceeds to manually pull the draw string, which is indirectly attached to the crankshaft by a clutch mechanism. When the clutch is engaged during startup, the crankshaft is forced to rotate, initiating the four stroke cycle. This means that there are four necessary steps or strokes needed to complete a cycle. These four strokes are the intake, compression, power and exhaust. The process begins when air is drawn through the air filter, where it then travels through the intake tube into the carburetor. When the air reaches the carburetor, gas is released through small jets, causing atomization to guarantee a saturated mixture of air and fuel. This mixture is regulated by the carburetor which is dependent upon the users desired operation speed. This is done by using a throttle valve to control the air flow. The mixture is then drawn into the engine through the intake valve during the intake stroke. The intake valve is controlled by the camshaft, which is driven by the crankshaft. The valve opens during the intake stroke, which starts with the piston at top dead center (TDC), meaning that the piston is at a position that is the farthest away from the crankshaft. The piston then starts traveling towards the crankshaft drawing the air-fuel mixture into the combustion chamber. When the piston reaches bottom dead center (BDC), meaning that the piston is at its closest position to the crankshaft, the intake valve closes. This is then the beginning of the compression stroke, during which the piston returns to TDC. The fuel-air mixture is compressed during this stroke to raise its temperature closer to its ignition point. When the piston reaches TDC for the second time, the power stroke is initiated. The piston then begins its return to BDC, when just passed TDC, a spark is generated from the spark plug. Spark is generated by a permanent magnet on the flywheel that rotates past a pickup coil. The spark then causes the mixture to combust, causing it to vaporize. The burning of the gas results in an increase of temperature, which causes the gas to expand. The expansion increases the pressure in the combustion chamber, which forces the piston back toward the crankshaft. When the piston reaches BDC for the second time it begins the exhaust stroke. The piston is then driven back towards TDC due to the rotational momentum of the crankshaft. As the piston returns to TDC the exhaust valve opens allowing the remaining gases to be forced out of the chamber. As the piston reaches TDC, the exhaust valve closes and the cycle repeats itself.

Revision as of 18:16, 3 December 2008

Contents

Tecumseh 5 HP Engine

Wholeengine.jpg



Executive Summary

This wiki documents the the three phases of the analysis of a 5 Horsepower Tecumseh engine. This engine was originally used to power a push lawnmower, but the analysis below begins after it had been removed from the mower body, and covers only components of the engine.

The first phase of this project focused on the disassembly and analysis of the motor's condition. It was determined that this motor probably did not run due to a faulty piston ring. During the second phase group members cataloged and analyzed each of the approximately 38 total parts.

The final phase of the project involved reassembling the motor, and reflecting on its overall design. Based on the understanding of the engine during the previous phases recommendations are made regarding the design, manufacturing, use, and life-cycle of the engine.

Introduction

This product was used to run a push mower. It is powered by an internal combustion that is used to spin the blades. Based on the condition of its parts this engine will not run, but this has not been tested.

Group Members:

Ian Kelsey - disassembly, reassembly, wiki creation

Dan Leake - disassembly, wiki creation

Kyle Johnson - disassembly, reassembly

Alex Lovallo - disassembly, reassembly, wiki creation, team leader

Sanket Chavan -


Product Description

  • 5 Horsepower Lawnmower Engine
  • Manufacturer: Tecumseh
  • Model Number:

Before Dissasembly

This 5 HP engine was used to power a pull start lawnmower. It was likely intended for urban or small yard use as it does not seem to have a drive system for its own locomotion. This engine once transformed chemical energy from combustion into linear kinetic energy using its piston. The connecting arm and crankshaft then converted this linear reciprocation motion into translational motion which could be used to power the mower blades directly, or may have been fed to the blades by a belt system.

It is possible that this engine will run as it does seem to have compression when the pull cord is pulled. While it is not possible for us to test this mower these is strong evidence that it will not run, or at least will only run for a short while until it breaks. The muffler of the engine is full of oil that will run out if it is tipped. This indicates that the piston rings may have failed and the engine is burning oil. Failed piston rings result in a lot of sediment build up from the burnt oil as well as increased piston friction which can significantly reduce the life of the engine. If enough heat builds up parts of the engine can melt rendering it inoperable.

Not including any fasteners it seems like that this engine will have roughly 40 parts. Viewing the exterior of the motor it is clear that plastic, and steel or iron have been used. Inside we expect to come across more iron, steel, rubber, and potentially some sort of textile.

After Disassembly

Disassembly Process

Step Number Process Tool Level of Difficulty
1 Unscrew (counterclockwise) the gas cap (part 1) from the gas tank (part 8). Hand Easy
2 Removed Rip Fence Bolt to Saw Blade Locking Lever By Hand Easy
3 Removed Removed Dust Blower Angle off of Dust Blower By Hand Easy
4 Removed Dust Blower and Rip Fence off of Casing By Hand Easy
5 Removed Rip Fence off of Casing By Hand Easy
6 Removed Plastic Blade Guard off of Casing By Hand Easy
7 Removed Casing off of Casing Philips-head Screwdriver Moderately Easy
8 Removed Gel Max Comfort Grip off of Casing By Hand Easy
9 Removed Shoe Plate Locking Gear off of Casing By Hand Easy
10 Removed Shoe Plate Locking Knob off of Casing By Hand Easy
11 Removed Trigger Switch off of Casing By Hand Easy
12 Removed Lock on Button off of Trigger Switch By Hand Easy
13 Removed Lock Spring off of Lock on Button Flat-head Screwdriver Easy
14 Removed Plastic Lock Washers off of Lock on Button Flat Head Screwdriver Moderately Difficult
15 Removed Switch Breaker off of Trigger Switch By Hand Easy
16 Removed 2 Cord Clamp Screws off of Cord Clamp off of Casing Phillips-head Screwdriver Easy
17 Removed Red Motor Connecting Wire off of Spring Loaded Graphite By Hand Easy
18 Removed Black Motor Connecting Wire from Spring Loaded Graphite By Hand Easy
19 Disassembled Spring Loaded Graphite Internals By Hand Easy
20 Removed Motor Screw From Casing Philips-head Screwdriver Easy
21 Removed Red Motor Connecting Wire From Armature By Hand Easy
22 Removed Black Motor Connecting Wire from Armature By Hand Easy
23 Removed Metal Gear From 1/4in. Plate By Hand Easy
24 Removed 1/4in. Metal Plate from Armature Shaft With Rotar By Hand Easy
25 Removed Small Metal Plate off of Armature Shaft With Rotar By Hand Easy
26 Removed Linear Oscillator from Metal Gear By Hand Easy
27 Removed Washer off of Gear from Metal Gear By Hand Easy
28 Removed Cylindrical Slider from Linear Oscillator By Hand Easy
29 Removed Blade Changing Piece from Blade Changing Component By Hand Difficult
30 Removed Blade Changing Spring from Blade Changing Component By Hand Easy
31 Removed Allen Wrench Screw from Blade Changing Component 3/32 Allen Wrench Easy
32 Removed Blade Changing Component from Linear Oscillator By Hand Easy
33 Removed Felt Piece from Linear Oscillator By Hand Easy
34 Removed Cylindrical Slider 2 from Linear Oscillator By Hand Easy

Component List

Part # Component Name Quanity Material(s) Manufacturing Process Description of Function Image Physical Description
1 Gas Cap 1 Plastic Injection Molded To seal the gas tank, by means of interior threading and a rubber gasket, to prevent leakage but yet allow air to pass into the tank to allow the free flow of gas out of tank
DSC00042.jpg
Red Colored. Round with vertical ribs for grip, interior threading. Contains interior rubber ring to create seal
2 Oil dipstick 1 Plastic, Steel Injection Molded, Stamped Used to check oil level in engine
DSC00041.jpg
Long steel stick with round plastic cap
3 Air filter cap 1 Plastic Injection Molded Holds air filter into place on engine block
DSC00043.jpg
Plain top surface and the lower surface has ribs to secure the air filter
4 Air filter 2 Foam, Cardboard Chemicals are mixed then a gas in pumped in to create air bubbles Filters air coming into engine
DSC00044.jpg
Main filter made of foam with a cardboard support
5 Hex-head bolts 2 Steel Rolled steel stock then stamped head to shape Holds air filter and cover into place
DSC00047.jpg
Cylindrical with threads and hex shaped head
6 Air filter housing 1 Plastic Injection Molded Houses air filter. Allows the air from the surroundings to enter and lets filtered air flow to the carburetor
DSC00050.jpg
Rectangular with an inlet pipe on one end and an outlet at the other
7 Hex-head bolts 8mm 3 Steel Rolled steel stock then stamped head to shape Holds gas tank onto engine block
DSC00051.jpg
Cylindrical with threads and hex shaped head
8 Gas tank 1 Plastic Injection Molded Holds gas
DSC00052.jpg
Tank is plastic and is molded to fit side of motor and is flat on other side
9 Dip stick tube 1 Plastic Injection Molded Allows access for dipstick to travel into the crank case to check oil level
DSC00053.jpg
Funnel-like at the top with an extended pipe
10 Pull cord with handle 1 Nylon cord with plastic handle Nylon- Thin composite that is weaved into cord, Plastic- Injection molded Used to manually start the engine by rotating a pulley which in return rotates the crankshaft and initiating the combustion process
DSC00054.jpg
Durable nylon fiber cord that winds around the pulley with a plastic handle at other end
10a Hex-head bolts 2 Steel Nylon- Thin composite that is weaved into cord. Plastic- Injection molded Holds pull cord cover on
DSC00056.jpg
Cylindrical with threads and hex shaped head
10b Pull cord assembly 1 Steel and plastic Housing is stamped steel, plastic pulley is injection molded, and engagement mechanism is stamped and die cast Transfers energy from pull cord to crankshaft
DSC00054.jpg
Circular cover made of steel with striations, an inner pulley made of plastic, and a spring loaded metal engagement mechanism
11 Hex-head bolts 3/8" 2 Steel Rolled steel stock then stamped head to shape Holds on fly wheel cover
DSC00056.jpg
Cylindrical with threads and hex shaped head
11a Hex-head bolts 8mm 2 Steel Rolled steel stock then stamped head to shape Holds on fly wheel cover
DSC00057.jpg
Cylindrical with threads and hex shaped head
12 Metal fly wheel cover 1 Steel Sheet metal stamped into form, as well as holes punched into top Protects user from moving fly wheel as well as allows for ventilation
DSC00058.jpg
Steel sheet metal with holes to allow for air flow
13 Crank case ventilation tube 1 Rubber Extruded through a die and then cut into sections Allows oil vapor and pressure from crank case to be vented to the air filter to be sent through the combustion process
DSC00059.jpg
Rubber hose
14 Spark plug 1 Ceramic, copper, aluminum, glass Assembled from variety of manufactured components Creates spark to initiate combustion
DSC00060.jpg
Physical: cylindrical, hex shaped at base. Threaded at one end. Ceramic Coating over portion. One end has electrical connection to plug, the other end has electrodes to produce sparks
15 Muffler with two 11 mm bolts 1 Steel, muffler is two separate pieces welded together 2 pressed pieces of sheet metal, extruded steel rods then thread rolling The muffler reduces engine noise by creating a resonating chamber
DSC00061.jpg
Silver color, inlet pipe on one side, small outlet holes on other side
16 1/2" hex-head bolts 8 Steel Extruded steel rods then thread rolling Use threading to secure engine components together
DSC00062.jpg
Black, small threads for metal use, hex shaped drive hole
17 Head 1 Cast iron Die-cast then machined Radiates heat from engine, seals combustion chamber. Has 8 holes to attach to head, 1 hole to allow spark plug, and 2 small holes to attach an external component
DSC00063.jpg
Square plate with parallel fins. 11 holes
17a Head Gasket 1 Aluminum Layered punched aluminum Creates a seal between the head and the engine block.
DSC00064.jpg
Flat, square with holes for bolts
18 Pick-up coil with rubber housed cord 1 Steel, rubber Thin pieces or sheet metal that are rolled, vulcanized rubber process to create hose. Spray coated with sealant afterwards Produces high voltage output pulses for firing the associated spark plug
DSC00065.jpg
U-shaped bracket surrounding a black cube. Both have layered steel in the ends. Spark plug wire comes from rear. Small strip for attaching grounding wire. Has plastic spray coating to seal the back side
19 Nut, washer and pull string catch 1 Steel Stamped and machined steel.washers are stamped from sheet metal, nuts are extruded then cut and bored out Teeth on interior cause rotation of crank when pull string is pulled to start motor.
DSC00066.jpg
cup shaped steel piece. With teeth on inside. Hole in top center for affixing bolt
20 Fly wheel 1 Cast iron Die-cast then machined down to specs Rotates mounted magnet past pickup coil creating alternating magnetic field inducing current
DSC00067.jpg
Round in shape, has vertical fins, magnet on one side, counter balance on other
21 Two 5/16" bolts and washers, throttle control and grounding wire 1 Steel, copper wire Throttle components stamped from sheet metal and bent. extruded steel rods then thread rolling, washers stamped from sheet metal, copper wire extruded Throttle connected to butterfly valve to control gas input to combustion chamber. Throttle cable holds throttle open while in operation. When the cable is not under tension the throttle closes because of attached spring breaking the electrical connection to pick up coil. Preventing spark stopping engine
DSC00068.jpg
Flat plate with hinge and spring to throttle control and grounding wire
22 Carburetor 1 Cast iron, steel , rubber Portion is die cast iron, stamped steel, extruded rubber Carburetor controls mixture of gasoline and air flowing to the combustion chamber. Cylidrical shape filters the gasoline before combustion
DSC00071.jpg
Cylindrical with rubber primer on side. One input for gas, two holes for air flow. Throttle butterfly valve on interior. Wire arm attached to throttle
22a Nuts and bolts 2 Steel Extruded steel rods then thread rolling, nuts extruded then cut and bored Holds carburetor into place
DSC00073.jpg
5/16"
22b Gas line 1 Rubber gas line Extruded rubber hose Provides a path for gas to flow from tank to carburetor
DSC00072.jpg
Rubber hose
23 Intake tube with gasket 1 Cast Iron Die cast Iron Transports the air from the carburetor into the engine. Gasket prevents leakage in joint between tube and carburetor
DSC00075.jpg
L shaped tube, with 2 bolt flanges on each end. Gasket matches flange shape
23a 3/8" bolts with washers 2 Steel Extruded steel rods that are thread rolled, washers are punched out Fasten intake tube to carburetor and engine block
DSC00076.jpg
Bolts
24 Valve cover, valve gasket 1 Steel bolts, steel cover with plastic gasket Stamped steel and stamped plastic Seals valve train
DSC00077.jpg
Steel cover, plastic gasket
24a 5/16" bolts 2 Steel Extruded steel rods that are thread rolled Holds valve cover to engine block
DSC00078.jpg
Bolts
25 Valve 2 Steel Machined from solid stock One valve controls air/fuel intake into combustion chamber. Second valve controls exhaust out of chambers
DSC00080.jpg
Long cylinder and thing with flattened head. Filleted near head
25a Valve spring 2 Steel Coiled, hot wound, and hardened in form Holds valves shut until proper time
DSC00081.jpg
Spring
25b Valve spring clip 2 Steel Punched Secures spring to valve
DSC00082.jpg
Two diameters of ring on top of each other. Smaller diameter can fit inside of spring. Has slot in middle for valve stem to slip into
26 drive pulley 1 Steel Machined Connects to crank shaft to use engine power to drive belt
DSC00083.jpg
Hollow cylinder with groove around outside edge and key way through inside
27 10 mm bolts with washers 6 Steel Extruded steel rods that are thread rolled Attached crank case to the motor block
DSC00084.jpg
Bolts
28 Key from crank shaft 1 Steel Stamped Hold drive pulley in line with crank shaft so they rotate together
DSC00085.jpg
Small half cylinder cut along long axis
28a Crank case pins 2 Steel Cut steel bar Align crank case bolts holes with the blocks bolt holes
DSC00086.jpg
Short cylinders with rounded ends
29 Crank case cover 1 Cast iron Die cast iron then machined Holds parts and oil inside crank case.
DSC00087.jpg
Rounded shape with holes to affix to crank case, holes for aligning pins, holes in center for crank shaft. Interior cavity to hold and align camshaft and camshaft aligner
30 Cam shaft 1 Cast iron Die-cast then machined Powered by crank shaft, has gear and lobes sized to open and close valves at proper time
DSC00089.jpg
Shaft with two lobes, a central gear, smooth and cylindrical on both ends
31 Valve lifters 2 Steel Welded and Machined Steel Are pushed up by lobes of cam shaft. When pushed up they open the valves in the combustion chamber
DSC00090.jpg
Flat plate with cylindrical shaft attached
32 Connecting rod cap 1 Cast aluminum Cast and then machined Holds the connecting rod to the crank shaft
DSC00091.jpg
Semi-circular curved bar with a bolt hole on either end. Inner surface is machined . Inside of surface is machined to reduce friction
32a 1/4" hex-head bolts 2 Steel Extruded steel rods that are thread rolled Fasten connecting rod cap to connecting rod over crankshaft
DSC00092.jpg
Bolts
33 Crank shaft 1 Cast iron with machined parts Cast and then machined to specifications Translates reciprocating linear piston motion into rotation
DSC00097.jpg
Cylindrical shaft with an offset cylinder in the middle, has two counter weights near middle
33a Washer 1 Steel Punched To reduce friction on the crankshaft Flat round ring made of steel
34 Connecting rod 1 Cast aluminum Cast the machined Connects the piston to the crankshaft transmitting the power
DSC00096.jpg
I shaped bar with circular hole on one end and semicircular groove on the other end that mirror the shaped of the connecting rod cap. Has a bolt hole on either side of the semi circular end to interface with the connecting rod
35 Wrist or gudgeon pin with a clip 1 Steel Pin is machined from solid stock, Clip is shaped and heated to hold form. Connects the piston to the connecting rod and provides a bearing for the connecting rod to pivot as it moves
DSC00094.jpg
Tube is a bored out cylinder and clip is shaped like a lowercase e
36 Piston 1 Aluminum Alloy Cast and machined to specifications. Transfers the force from combustion gas in the cylinder to the crankshaft via the connecting rod. Forces exhaust out of exhaust valve and draws the air fuel mixture into the combustion chamber. Compresses the air/fuel mixture pre-combustion
DSC00095.jpg
Cylindrical with flat plane on one end. Has lateral hole to allow wrist pin. Has grooves in side for piston rings and a hollowed interior to reduce mass
36a Piston Rings 3 steel and coated steel Punched steel, One ring has a spring coating along outside edge Seal the combustion chamber/ Support heat transfer from the piston to the cylinder wall/ Regulate engine oil consumption
DSC00093.jpg
Each ring has one gap. One ring is not solid steel but has a composite material insert
37 Engine block 1 Cast iron Die cast and machined to specifications Houses all of internal engine parts
DSC00099.jpg
Hollowed rectangle with fins
38 Cam shaft aligner 1 Plastic ring with stainless steel rod in it Machined steel, injection molded plastic Holds one end of the cam in place to insure that the teeth between the crankshaft gear and camshaft gear align
DSC00098.jpg
Plastic ring with extruded tube off one side with a steel insert in it


Assembly Process

Step Number Process Tool Level of Difficulty
1 Remove 7 Phillips-head screws Phillips-head Screwdriver Easy, 1 Screw Quite Difficult
2 Removed Rip Fence Bolt to Saw Blade Locking Lever By Hand Easy
3 Removed Removed Dust Blower Angle off of Dust Blower By Hand Easy
4 Removed Dust Blower and Rip Fence off of Casing By Hand Easy
5 Removed Rip Fence off of Casing By Hand Easy
6 Removed Plastic Blade Guard off of Casing By Hand Easy
7 Removed Casing off of Casing Philips-head Screwdriver Moderately Easy
8 Removed Gel Max Comfort Grip off of Casing By Hand Easy
9 Removed Shoe Plate Locking Gear off of Casing By Hand Easy
10 Removed Shoe Plate Locking Knob off of Casing By Hand Easy
11 Removed Trigger Switch off of Casing By Hand Easy
12 Removed Lock on Button off of Trigger Switch By Hand Easy
13 Removed Lock Spring off of Lock on Button Flat-head Screwdriver Easy
14 Removed Plastic Lock Washers off of Lock on Button Flat Head Screwdriver Moderately Difficult
15 Removed Switch Breaker off of Trigger Switch By Hand Easy
16 Removed 2 Cord Clamp Screws off of Cord Clamp off of Casing Phillips-head Screwdriver Easy
17 Removed Red Motor Connecting Wire off of Spring Loaded Graphite By Hand Easy
18 Removed Black Motor Connecting Wire from Spring Loaded Graphite By Hand Easy
19 Disassembled Spring Loaded Graphite Internals By Hand Easy
20 Removed Motor Screw From Casing Philips-head Screwdriver Easy
21 Removed Red Motor Connecting Wire From Armature By Hand Easy
22 Removed Black Motor Connecting Wire from Armature By Hand Easy
23 Removed Metal Gear From 1/4in. Plate By Hand Easy
24 Removed 1/4in. Metal Plate from Armature Shaft With Rotar By Hand Easy
25 Removed Small Metal Plate off of Armature Shaft With Rotar By Hand Easy
26 Removed Linear Oscillator from Metal Gear By Hand Easy
27 Removed Washer off of Gear from Metal Gear By Hand Easy
28 Removed Cylindrical Slider from Linear Oscillator By Hand Easy
29 Removed Blade Changing Piece from Blade Changing Component By Hand Difficult
30 Removed Blade Changing Spring from Blade Changing Component By Hand Easy
31 Removed Allen Wrench Screw from Blade Changing Component 3/32 Allen Wrench Easy
32 Removed Blade Changing Component from Linear Oscillator By Hand Easy
33 Removed Felt Piece from Linear Oscillator By Hand Easy
34 Removed Cylindrical Slider 2 from Linear Oscillator By Hand Easy

After Assembly

Engine Operation

This engine was designed as a small 4-stroke engine, which was most likely used to power a push mower. The operation of this product begins initially with the startup. This is done when the operator presses the primer bulb a few times, which causes gas to be forced into the carburetor and also removing any air in the fuel line. The operator then proceeds to manually pull the draw string, which is indirectly attached to the crankshaft by a clutch mechanism. When the clutch is engaged during startup, the crankshaft is forced to rotate, initiating the four stroke cycle. This means that there are four necessary steps or strokes needed to complete a cycle. These four strokes are the intake, compression, power and exhaust. The process begins when air is drawn through the air filter, where it then travels through the intake tube into the carburetor. When the air reaches the carburetor, gas is released through small jets, causing atomization to guarantee a saturated mixture of air and fuel. This mixture is regulated by the carburetor which is dependent upon the users desired operation speed. This is done by using a throttle valve to control the air flow. The mixture is then drawn into the engine through the intake valve during the intake stroke. The intake valve is controlled by the camshaft, which is driven by the crankshaft. The valve opens during the intake stroke, which starts with the piston at top dead center (TDC), meaning that the piston is at a position that is the farthest away from the crankshaft. The piston then starts traveling towards the crankshaft drawing the air-fuel mixture into the combustion chamber. When the piston reaches bottom dead center (BDC), meaning that the piston is at its closest position to the crankshaft, the intake valve closes. This is then the beginning of the compression stroke, during which the piston returns to TDC. The fuel-air mixture is compressed during this stroke to raise its temperature closer to its ignition point. When the piston reaches TDC for the second time, the power stroke is initiated. The piston then begins its return to BDC, when just passed TDC, a spark is generated from the spark plug. Spark is generated by a permanent magnet on the flywheel that rotates past a pickup coil. The spark then causes the mixture to combust, causing it to vaporize. The burning of the gas results in an increase of temperature, which causes the gas to expand. The expansion increases the pressure in the combustion chamber, which forces the piston back toward the crankshaft. When the piston reaches BDC for the second time it begins the exhaust stroke. The piston is then driven back towards TDC due to the rotational momentum of the crankshaft. As the piston returns to TDC the exhaust valve opens allowing the remaining gases to be forced out of the chamber. As the piston reaches TDC, the exhaust valve closes and the cycle repeats itself.

The assembly of this engine was nearly the reverse of the disassembly and went much more smoothly.Using our disassembly directions it was much easier to find the proper socket sizes to apply to each fastener. The only notable difference was during the assembly of the valve springs. While removing the valve clips was very simple inserting them was much more difficult. The valve clips attach the valve springs to the valves. Reinserting them requires either a valve spring compressor tool or two sets of hands.

Besides the difficulty with the valve springs the assembly was much easier than the reassembly. At times the disassembly required the use of brute force and in some situations multiple hammers to remove components that had become firmly attached over the last 2 - 3 decades. Since these natural adhesives had been overcome and cleaned away the assembly went smoothly and was completed in 2.5 hours.

References