Group 29 - 5 HP IC Motor

Latest revision as of 16:20, 5 December 2008

Tecumseh 5 HP Engine

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 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, wiki creation

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

Sanket Chavan -

Product Description

• 5 Horsepower Lawnmower Engine

• Manufacturer: Tecumseh

• Model Number: VS120 63063E

Before Dissasembly

Purpose and Operation

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.

Disassembly Process

After Disassembly

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		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		Long steel stick with round plastic cap
3	Air filter cap	1	Plastic	Injection Molded	Holds air filter into place on engine block		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		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		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		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		Cylindrical with threads and hex shaped head
8	Gas tank	1	Plastic	Injection Molded	Holds gas		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		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		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		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		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		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		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		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		Rubber hose
14	Spark plug	1	Ceramic, copper, aluminum, glass	Assembled from variety of manufactured components	Creates spark to initiate combustion		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		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		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		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.		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		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.		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		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		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		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		5/16"
22b	Gas line	1	Rubber gas line	Extruded rubber hose	Provides a path for gas to flow from tank to carburetor		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		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		Bolts
24	Valve cover, valve gasket	1	Steel bolts, steel cover with plastic gasket	Stamped steel and stamped plastic	Seals valve train		Steel cover, plastic gasket
24a	5/16" bolts	2	Steel	Extruded steel rods that are thread rolled	Holds valve cover to engine block		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		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		Spring
25b	Valve spring clip	2	Steel	Punched	Secures spring to valve		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		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		Bolts
28	Key from crank shaft	1	Steel	Stamped	Hold drive pulley in line with crank shaft so they rotate together		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		Short cylinders with rounded ends
29	Crank case cover	1	Cast iron	Die cast iron then machined	Holds parts and oil inside crank case.		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		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		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		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		Bolts
33	Crank shaft	1	Cast iron with machined parts	Cast and then machined to specifications	Translates reciprocating linear piston motion into rotation		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		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		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		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		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		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		Plastic ring with extruded tube off one side with a steel insert in it

CAD Models

Part #	Component Name	CAD Drawing
1	Piston Head
2	Compression Ring
3	Oil Ring
4	Wrist Pin
5	Connecting Rod
6	Connecting Rod Cap
7	Connecting Rod Cap Bolt

Assembly Process

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.

Product Testing and Analysis

Based on the nature of our product and the fact it has quite a few moving parts, fairly precise models would need to be made in order to evaluate the product. In terms of various models that would need to be analyzed, analytical ones would be the most important and beneficial but graphical models would also be useful. These graphical models can be in the form of CAD drawings, or 3D modeling such as Solid Works. While these models are helpful the most important are the analytical models such as fatigue, power transmission, thermodynamic, stress/strain as well as others. With our product being an engine many of these models need to be performed and analyzed before the engine is manufactured on a large scale.

Fatigue models would need to be performed on various parts of the engine such as the cylinder walls, pistons, piston rings as well as the engine block itself. These are necessary because if some of these parts fail the whole engine could fail. For example if any of the rings fail the engine could either lose compression or oil could leak into the combustion chamber and cause the engine to burn oil. Also, power transmission models would need to be analyzed to look at how power is transferred from combustion to the pistons, then to the crank shaft then to the blades. Along with the power transformations, possible power losses would need to be tested. Thermodynamic/heat transfer models would also have to be tested and analyzed because our engine being internal combustion it creates a lot of heat. The engine block itself has “fins” on it in an attempt to dissipate heat. For engineers to know whether these fins properly dissipate heat or dissipate enough of it these models need to be looked at. Fluid flow models, while not as important as the others would also need to be analyzed. The only model that would need to be looked at would be the transfer of fuel from the tank to the carburetor. A rubber hose connects these two components and would need to be tested to ensure proper flow as well as is there were possible restrictions such as a kink.

Lastly and possibly the most important model that would need to be tested would be the materials stress/strain model. There are various different components in our engine that are made of different materials. Each of these components has a different use and some need to be able to handle certain stresses and strains. For example, our engine block is made of cast iron. This is so because with the engine block being internal combustion the block needs to be able to handle higher stresses and strains. This piece as well as other various components needs to be tested numerous times and for long period of times in order to ensure that they do not fail under repeated use. All of these models need to be fairly precise and when combined would provide a larger detailed model of how the whole engine may perform under hard repeated use.

Process Comparison

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.

Design Changes and Recommendations

This motor is very heavy and would be exhausting to push around. One of the biggest things that could be done to improve this engine is to decrease the over all weight and the over all package size. Most of the materials could be lightened by using aluminum or some other alloy and still have the strength needed. Parts such as the gas tank could be redesigned to compact the entire package, other parts can be completely removed. The intake tube between the carburetor and the engine block can be taken out and the carburetor can be bolted directly to the block. This would reduce cost of manufacturing. Almost all of the rotating components could be reduced in weight this would allow the motor to reach operating speed faster, rev higher, and increase power by decreasing the rotating mass. The piston head and cylinder can be increased in diameter to increase displacement and increasing power. A switch to a fuel injection system would help improve fuel economy because the amount of fuel and the timing of fuel can be controlled. The muffler could be improved to have more baffels in it to make the engine quieter and more comfortable for the user. Air flow could be improved by porting the heads and using bigger valves, this would increase the power of the motor by making it easier for it to get the air and fuel in and out.

References

Four Stroke Engine. Retrieved November 3, 2008, from http://en.wikipedia.org/wiki/Otto_cycle#The_Otto_cycle.

Injection Molding. Retrieved november 13, 2008, from http://en.wikipedia.org/wiki/Injection_molding.

Casting. Retrieved November 12, 2008, http://en.wikipedia.org/wiki/Casting

US Patent Database Search. Retrieved November 14-25 http://patft.uspto.gov/