Project Management: Critical Project Review
Our group has suffered many mistakes due to lack of knowledge. Although not all of our issues in the past have been entirely our fault, we have no one to blame but ourselves. Communication is a key factor in a successful group and we believe our group lacks good communication. Our past problems were, we could not find the time to meet and work as a group, but we found that there is another problem; we are lazy. We knew gate 4 was due soon, but all of us thought that it was the oral presentation in class. No one bothered to check ublearns if that was the case. When we find out what gate 4 was the reassembling of the engine, it was already too late. The TA’s office hours were no longer available, so we are forced to skip the reassembly. Our solution to the problem is having someone communicate with the group at least once a day. We were forced to learn the Ta's office hours and memorize it. For the reassembly, we plan to reassemble the engine even after gate 4 is due.
Our group has a tendency to work on our gates last minute. Although we know it is a bad habit, we still end up doing the same thing. This results in poorly constructed wikis, and lack of information. In order to fix this problem, we read through all comments and notes that are given to us on our graded wikis, and take all the information into consideration. We plan on spending more of our free time together as a group and complete the gates earlier then the due date.
Our previous problem in our group was meeting up at a time where we are all free. We have solved this by learning each other’s schedule. We know what times we are free and we are planning to use more of that time to work on our gates together.
Product Archaeology: Product Explanation
The tables below will show the steps taken to reassemble the lawn mower engine and will consist of the following data.
Step: The step number as well as what parts are being reassembled in the step.
Reassembly Details: A short summary of what was done during that specific step in the reassembly process.
Difficulty: The difficulty of each step will be represented on a scale from 1 to 4 explained below. A description of why each step was giving a rating will be included as well.
- 1 - very easy step
- 2 - easy step but more components to reassemble
- 3 - medium difficulty, some trouble reassembling parts
- 4 - hard to reassemble, difficult to get back into place, time consuming
Tools Used: Lists and describes each tool used in each step.
Original Assembly: Describes how the parts were originally assembled on the production line.
Comparison to disassembly: Describes how the reassembly process was more or less difficult than the disassembly process and why.
Image: A picture of the reassembled part.
|Step||Reassembly Details||Difficulty||Tools Used||Original Assembly||Comparison to disassembly||Image|
|1) Piston and Connecting Rod||The connecting rod was put back onto the shaft under the piston head. The Piston was then put back into the cylinder. To be able to slid into the cylinder the gaskets on the piston were pushed flush into the piston using pliers.||
||Some type of machine was used to push in all the rings while it was pushed in. The piston also may have been lubed before assembly to prevent scratches.||Harder than disassembly because the piston did not easily slide in due to the piston rings being in the way.||
|2) Cam Shaft and Crank Shaft||The two shafts were placed into their respective holes in the engine block and gears were aligned. A socket wrench was used to bolt the clamp encasing the crankshaft to the connecting rod.||
||During original assembly both shafts were put in the same way except maybe with machines.||Only difference with disassembly was using a gear-puller to free the crankshaft from the engine block.||
|3) Oil Pan and Engine Block||The Oil pan was aligned with the shafts in the engine block and was bolted on with 6, 3/8inch bolts. The Oil drain plug was screwed back in as well.||
||Once all the inner working of the engine were inside the engine block the oil pan was bolted on using an industrial hydraulic torque wrench.||This process was very similar to the disassembly|
|4)Oil Filter||Two bolts were bolted in using a socket wrench and the hose was reattached.||
||Worker placed filter in and breather hose was screwed on.||Same as disassembly process, just dealing with 2 screws|
|5)Flywheel/Magneto Assembly||The magneto was put back on with 2 screws using a Philips-head screwdriver. The flywheel was then carefully positioned over top the magneto and pushed down into place. The flywheel was then bolted down with an 11/16th in bolt in the center.||
||Worker or machine screwed on magneto then flywheel over top.||Same as disassembly, except the magneto was put on first then the flywheel over it.||
|6)Valve-Spring Cover||Two bolts were used to hold the cover on.||
||cover was screwed on by worker, just like we did.||Screwing during assembly and unscrewing during disassembly were the only difference|
|7) Heat Sink||The head gasket was placed above the piston then the heat sink was bolted on top of the gasket to the engine block using a socket wrench.||
||A torqe wrench was used to tighten bolts, as it is faster than other simpler wrenches.||Only difference in putting the heat sink back on was aligning it with the head gasket.||
|8) Carburetor Assembly||Intake gasket was placed over hole and carburetor was place on engine block and fastened with 2 5/16th in bolts using a socket wrench.||
||Similar to our process, simply fastening bolts||Screwing during assembly and unscrewing during disassembly were the only difference||
|9) Metal Housing and Spark Plug||The metal housing for the engine was reassembled by screwing in 2 phillips screws with crush washers and 2 5/16th inch bolts with crush washers. The spark plug was then screwed in and the wire for the spark plug was attached with a simple clip.||
|Worker used torque wrench to quickly put on housing and spark plug was screwed in.||Screwing during assembly and unscrewing during disassembly were the only difference|
|10)Dipstick Housing||Used socket wrench to bolt on 3/8 inch bolts||
||Worker simply screwed on housing||Screwing during assembly and unscrewing during disassembly were the only difference|
|11) Pull-start Assembly||First the coil had to be put back into its housing. The coil was hard to work with but was put back using 2 people, 4 hands, to hold the outer edges of the coil down while the center was coiled back in on itself. The cap was then screwed on over the coil to keep it in place. The gear part was the bolted back onto the bracket and the bracket bolted back onto the engine with 2 5/16th inch bolts.||
||Coil was put in by machine, therefore was much easier to put into place. A worker would have screws on bracket and cap.||No trouble in disassembling this part but alot of trouble tring to get coil back in.||
|12) Gas Tank||The gas tank was slid onto the metal housing onto grooves. It was then bolted with 5/16th inch bolts and the gas line was reattached with a circular clamp. The dipstick was then put into the engine as it would have been in the gas tanks way if put in before.||
||Very similar to are own process with the exception of faster tools to bolt gas tank on.||Screwing during assembly and unscrewing during disassembly were the only difference|
If we were to redesign the engine from the ground up and make it a V2 (a two cylinder engine in a V shape as shown in figure 1 below) with two smaller cylinders instead of a one-cylinder engine it would drastically improve performance. While this would require more components and increase the size of the engine, it would improve its performance and efficiency, befitting the engines societal, economic and environmental appeal. Since a lawn mower engine does not require a large amount of horsepower to spin the blades this V2 design could use smaller piston-cylinders then the current size of our current piston-cylinder. Using smaller pistons would help keep the cost increase of adding components to a minimum and minimize the effects of the negative change on the economic design factors. This design would require a second cylinder, piston, connecting rod as well as two more valves, valve springs, and valve pushers. The crankshaft would also have to be altered to have a second mount for the second connecting rod. Having two cylinders keeps the engine from relying only on momentum to keep it moving during the upstroke because the cylinders would be at different points in the combustion cycle as shown in figure 1 below. The second cylinder can drive the engine while the first cylinder is on its upstroke minimizing the inefficiencies of the engine.
Our second system wide change would be removing the pull start assembly and replacing it with and electronic push button ignition system. Once again this would increase the production cost and negatively affect the engines economic appeal, but its ease of use would increase which benefits its societal design factors. Making this change would require both the replacement of the pull start with and electric motor but also attaching the appropriate start and stop button as well as a battery to run the electric start assembly. So the battery will be constantly recharged a generator (aside from the spark generator for the spark plug) would need to be attached to the magneto to supply the battery with power. These changes may significantly increase the engines cost, but allow those who are weak or have minor disability the ability to use the lawn mower with much less effort and more safety (less risk of injury) because we found it very difficult to pull. This change would improve the ease of use for everyone. One example of a generic starting circuit is shown in Figure 2 below.
If the engine were cooled better it could increase the longevity of the engine and resistance to heat fatigue. Our current engine has no radiator or cooling system other then the heat-sinks mounted around the piston-cylinder compartment. These allow the engine to cool naturally by convection and radiation from the heat-sink to the surrounding air, but the engine would need to get rather hot before significant heat loss would occur because convection rate only becomes significant when temperature differences are significant. While the engine can handle these temperatures over time, high temperatures could functionally anneal its components, softening them and eventually lead to component failure. Several components in our engine were broken, damaged or scared severely. We propose that a mechanical fan cooling system is installed in the engine. This would require the addition of a fan belt assembly and some type of belt driver to a rotating component on the engine. This would require little change to the engine itself but could have large effects on its cooling rate. This change would add some minor cost, negatively affecting the economic design factors, but could improve its longevity and replacement costs, which is an economic positive. It also could benefit its societal and environmental appeal by lasting longer and leading to less waist because of less disposal and replacement. An Diagram of a fan cooled system is show below in Figure 3.