Gate 2.
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Gate 2, Excavation
Project Management: Preliminary Project Review
As we worked on disassembling our engine most of our work went according to plan as we expected. We all had our roles to play in the completion of the project an its analysis, with Tyler Lynn working as project manager, Tim Li keeping us connected as communication liaison, Dylan McCann's guiding wisdom as technical adviser, and Garrett Lust taking notes and preparing our final presentation as editor. Our combined work and school schedules did make it difficult at time to find time to get all for of us together in the lab often, but there was really only one major issue that came up in our disassembly as we worked to complete it. As we worked to disassemble our engine we came to a point were we could not remove the shaft from the engine block without removing a bearing at one end or a gear on the other. We were unable to remove either with any of the tools we had at our disposal and we tried for some time to remove it. We decided we might be able to use a gear puller, but we were unable to get one from the Machine shop as it was closed. We were finally able to get a response from the Machine shop and sign one out on the morning of October 28, but through a series of school, work scheduling conflicts, and poor communication, we were unable to meet in the remaining office hours to complete the disassembly. Our group worked well together. When we began the project we had a good understanding and plan to complete this section. Everyone worked hard and gave their fair share. In the future we will attempt to analyze and plan ahead for things that we think we may not be provided that may need if issues arise. We plan to sit down and make a list of tool for the reassembly gate to ensure that we will have everything we need to complete it before we being the work on the gate to avoid future scrambling to find tools that we need. Scheduling meeting times may still be an issue as some of our work schedules rotate, but in the future we may need to have parts of the group meet separately if necessary to attempt to get around scheduling conflicts and traveling issues.
Product Architecture, Product Dissection
This is a step by step process of the dis-assembly of a lawn mower engine.
All parts removed from the lawn mower engine are not intended to be removed by the consumers, with the acception of the gas cap and dipstick used for fueling and maintenance purposes.
The difficulty of each step is given in terms of easy, medium and hard. Easy requires little dis assembly work (ex. a couple of screws or bolts, no unusual tools or set up ). Medium requires other parts to be removed to allow for the part to come off or may require more then one person to help with the removal. Hard means that difficulties were present in taking out parts and that much time was used or many different tools were tried before removal was a success.
To dissemble the engine the following tools were used:
- Socket wrench
- Sockets (5/16th inch, 1/2 inch, 3/8 inch, 11/16 inch)
- Screwdriver
- Gear Puller
| Step | Component | Difficult | Disassembly process | Tools Used | Image | ||||
| 1 | Gas Tank | medium | The first part taken off the engine was the gas tank. Using a socket wrench and 5/16th inch socket the tank was removed by taking out 2 bolts. The gas line was then detached from the tank. It was attached with a small circular metal clamp. When trying to take off the tank the oil dipstick cap was in the way. The dipstick itself was taken out and the gas tank was able to come free. However, the pull cord went through the tank and had to be untied where the pull cord handle was so it could slid through the tank. |
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| 2 | Pullstart Assembly | Difficult | The next part removed was the crankshaft assembly. Two screws were removed to take the cap off. The coil spring inside was then carefully detached by sliding it out of its compartment. The next part became difficult as the bolt in the center of the rotating gears could not be turned without the entire system freely rotating. We went on to take off the bracket holding on the pull start assembly. Three bolts were removed with a socket wrench. After trying the center bolt again, while holding the freely rotating system, the bolt broke due to torsion. This however did allow the assembly to come free. |
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| 3 | Dipstick Housing | easy | The dipstick housing was removed by taking out 2 bolts. |
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| 4 | Metal Housing | medium | The metal housing for the engine was removed by first taking out 2 phillips screws with crush washers and 2 5/16th inch bolts with crush washers. To fully remove the housing the spark plug and attached wire had to be removed. The spark plug was screwed out. |
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| 5 | Carburetor Assembly | medium | The whole carburetor assembly was removed with 2 phillips bolts the fuel line was removed from the engine by pulling it off and was kept on the carburetor assembly. Underneath it was found that the intake gasket was already broken. |
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| 6 | Heat Sink | medium | A total of 7 half inch bolts were removed from the heat sink on the top of the engine. Underneath was a gasket. |
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| 7 | Valve-Spring Cover | easy | Two phillips bolts were taken out to remove the valve spring cover. |
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| 8 | Flywheel/Magneto Assembly | hard | The flywheel/Magneto assembly was held on by a single 11/16th inch bolt which was removed with a socket wrench. After the bolt was removed the flywheel still would not come off. We hit a dilemma since we did not have the correct tool such as a pry-bar to remove flywheel. A hammer had to be used to slowly and carefully pry it off. This took about 5 minutes. Inside was a magneto assembly which was removed by taking out 2 philips screws. |
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| 9 | Oil Filter | easy | Two bolts were taken out using a socket wrench and the hose was detached. |
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| 10 | Oil Pan/ Bottom of Engine | hard | One 1/2 inch bolt was removed using a socket wrench. This bolt ended up being the oil drain plug. An additional 6 3/8th inch bolts were removed with the socket wrench to dissemble the oil pan. To completely remove the bottom of the engine, the pulley on the drive shaft had to be removed to allow the bottom of the engine to come off. To get the pulley off a gear-puller was used, this took some time. |
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| 11 | Oil Pump and Cam shaft | easy | The oil pump and camshaft where simply taken out of the engine block. They were only held in place by holes in the engine block. |
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| 12 | Crankshaft | medium | The clamp holding the piston connecting rod to the crankshaft was removed by using a socket wrench on two blots. The Crankshaft was able to slid right out of the engine block. |
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| 13 | Piston and Connecting Rod | medium | The piston was slowly slid out of the cylinder by pushing from the inside of the engine block on the connecting rod which was still attached to the piston. A hammer was used to keep the piston aligned in the chamber while it was pushed through. After coming out the connecting rod was detached from the piston by removing a fastener on the piston by hand. |
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Subsystem connections
Fuel tank to carburetor
The carburetor controls air and fuel intake. It is physically connected to the engine and a mass flow of air passes through it to the combustion chamber. The fuel is poured into the fuel tank and is forced into the system by a primer. It mixes the air and fuel to the proper ratio. It starts off as mass and potential chemical energy and is transferred to the carburetor through mass transfer. The mixture is then transferred to the combustion chamber where it is converted from mass energy to thermal and pneumatic energy through the chemical reaction of combustion. The connection of a fuel tank and the carburetor is necessary because a constant intake of fuel is needed in order for the engine to run. When designing the carburetor and the fuel tank, engineers wanted the parts to last as long as possible without breaking as longevity affects it societal design considerations. Fuel is expensive and should not be wasted as fuel use affects both economic and environmental concerns; therefore the fuel tank is used to hold fuel so the fuel does not evaporate or become contaminated and burn less efficiently. The fuel line is made of plastic allowing more flexibility for the fluids to flow. Video 1 below is and externally linked youtube video that we have included to show the motion of the piston and valves and their relation to one another as pneumatic energy from combustion drives the piston up and down.
Video 1: Opening and Closing of Valve Intake
Pull-start to Crankshaft
The pull start is made up of a rope, handle, and a gear assembly. The handle allows the ease of human energy transfer. The rope is connected to the gear to transfer human energy to rotational energy. This pushes a gear with a threaded center outward connecting the gear the crank shaft physically (shown in Video 2 below). The gear uses human energy to convert to rotational energy. This connection was mostly an economical concern but also needs to be designed safely which affects its societal design concerns. Human energy is the most convenient energy form. It is the most portable and can be found anywhere a person needs to use the machine. This type of connection is used so that human energy can be transferred into the system. Video 2 below is and externally linked youtube video that we have included to show the mechanics of the pull start assembly as it is pulled.
Video 2: Pull Start to Crankshaft
Spark system
The spark system is designed to create voltage without the use of a battery. This voltage is produced by the use of a magneto. A magneto is basically the opposite of an electro magnet. By moving a ferromagnetic attached to the inside of flywheel past an armature of coiled wire, the magneto produces voltage repeatedly at a certain part of the rotation of the engine. This time interval coincides with the interval that spark is required to create combustion because the flywheel that contains the magnet is directly connected to the engine’s crankshaft, and it rotates externally at the same RPM as the engine. This is a combination of an energy flow that acts as signal for combustion as well as its combustion source. The voltage is transferred to the spark plug by a wire and then is converted to spark by the spark plug. The design of this component of the engine was not heavily influenced by environmental, or global concerns other then recyclability (environmental), but is a cheep way to regulate combustion timing and therefore affects economic concerns. Safety from electrical shock is also a concern affecting its societal considerations. There are no emissions created by this system and it only needs rotation of the engine to operate.
Connections of subsystems
The subsystems are connected by the initiation of the pull start assembly. The pull start assembly is connected to the crankshaft directly, and uses human energy to begin rotation. On the other side of the engine the crankshaft is connected to the flywheel which contains a magneto. The magneto generates a spark through rotation. Then spark plug is connected to the system by a wire. The spark plug generates a spark for combustion in the pistons. It transfers electrical energy to pneumatic and thermal energy. The carburetor and the fuel tank are physically connected through a rubber tube. This allows mass flow and energy flow from the tank to the carburetor. All of these subsystems are connected by the combustion chamber. The Engine is initiated by pulling the pull start which turns the crankshaft moving the piston and open the valves allowing fuel and air flow. The fuel and air from the carburetor enter the cylinder and are ignited by the spark generated by the spark system being turned by the crankshaft. The combustion then drives the engine through this cycle all over again.
Arrangements of subsystems
There is a reason for every arrangement of the subsystems. If the placement was rearranged then the systems can either harm or destroy the other subsystems. The fuel tank cannot be adjacent to the combustion chamber or heat. This will cause the fuel to evaporate or ignite. The spark plug should be kept away from the fuel tank because it can ignite the fuel inside. The mount for the blade should only be placed on the bottom of the engine to allow only the cutting of grass and not harm the engine.
