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Victa 2-Stroke Engine Block – Manufacturing Engineering

Introduction: The Victa 2-stroke engine is an extremely important engine design as it is simple yet useful for everyday products which rely on a motor to operate. Engines require a complex set of parts to operate. Not only do engines require a few parts but they also require constant maintenance and products such as coolants, oil, fuel etc. Most machines that require a constant driving force or rely use an engine. All machines that require the use of motors to operate also use engines unless they use batteries or electric power. Applications for 2-stroke engines include lawnmowers, line trimmers, chainsaws and even jet skis. Advantages of 2-Stroke Engines: Another type of motor that is applied in many pieces of machinery is the 4-stroke engine. There are several advantages that the 2-stroke engine has over the 4-stroke engine. 2-stroke engines are much lighter than 4-stroke engines due to several reasons. Mainly, 2-stroke engines do not require as many valves as 4 stroke engines. 2-stroke engines do not require coolant as they are designed to cool down using the flow of air. The minimisation of valves decreases the weight of the engine. Also, since in 2-stroke engines the power stroke is every second stroke and in 4-stroke engines the power stroke is every fourth stroke, 4-stroke engines do not have a very consistent power and so a heavy wheel is required to help maintain the power. Two stroke engines also have a higher power to weight ratio. This is due to the fact explained above where the power stroke is evident every second stroke and thus a higher and more consistent power is produced. Therefore, the power in 2-stroke engines is double that than 4 stroke engines since the power stroke occurs twice as often. 2-stroke engines also cost less money to manufacture since the design is not as complex. Disadvantages of 2-Stroke Engines: Although 2-stroke engines have certain advantages over the 4-stroke engine, there are still several disadvantages. 2-stroke engines may be lighter due to the fewer valves and less complication design, but this means that an effective lubrication system is absent and hence 2-stroke engines wear out a lot faster than 4-stroke engines. Also, 2-stroke engines use a lot of oil compared to 4 stroke engines. Since 2-stroke engines complete their power stroke every second stroke, the fuel does not last as long as it does with 4-stroke engines. Furthermore, 2 stroke engines produce much more smoke than 4 stroke engines. This is due to 2 reasons. Firstly, the burning of both oil and fuel in the 2stroke engine can cause a massive amount of smoke to be produced. Secondly, as seen in the figure to the right, when fuel/oil/air is injected into the combustion chamber, a small amount leaks into the exhaust port which is extremely harmful to the environment. From these reasons, 4 stroke engines are overpowering 2 stroke engines and slowly causing them to become obsolete and because of the more efficient use of fuel and petrol and the fact that they create less pollution has resulted in their use in cars and buses.

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Victa 2-Stroke Engine Block – Manufacturing Engineering

The international standard which 2-stroke engines are manufactured using is SAE (Society of Automotive Engineers) Test standard J1940.

Parts Of The Engine: A basic 2 stroke engine is made up of several main components. These components all work together to operate the engine. 1. Spark plugs – the spark plugs are a device used to send an electric current from the ignition to the combustion chamber. The spark plugs ignite the fuel/air mixture in the combustion chamber and are the reason combustion occurs in petrol engines. In diesel engines however,

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spark plugs aren t needed since the combustion occurs when the fuel/air mixture is compressed. Combustion chamber – this is where combustion occurs. The piston lowers, and fuel/air mixture enters the combustion chamber. Once the spark plugs ignite the mixture combustion occurs. Exhaust outlet – the exhaust outlet is where gases after combustion has occurred exit the combustion chamber. Fuel intake – this is where fuel enters to get to the combustion chamber. When the fuel intake allows fuel to pass through, the fuel stays in a section of the engine until the valve connecting that section to the combustion chamber is opened and then fuel is passed to the combustion chamber. Piston – the piston is a ‘mechanical arm’ which cranks back and forth in the engine. The piston is connected to the crank shaft, so it can move up and down. The movement of the piston controls several processes; the process of fuel being injected into the combustion chamber, the process of combustion gases exiting the exhaust port and the process of combustion since it controls the compression of the fuel/air mixture. Crank shaft / crank – transfers mechanical energy to the piston. The crankshaft/crank control the movement of the piston and the speed of the movement of the piston.

In the production of the engine block, it is crucial that all measurements are precise and accurate. The importance of the measurement and accuracy of each part is mainly due to the fact that the engine will have combustion occurring and so the strength of the material and the size of each part is important as minor inaccuracies can result in damage to the engine or the engine block and also can result in the combustion not occurring as efficiently and safely as possible. The surface integrity must also remain consistent. The surface integrity is the condition of a materials surface after it has undergone modification from a manufacturing process. The condition of the material’s surface must remain the same or very similar in order for the material to hold its physical and mechanical properties which in this case is crucial in ensuring the engine block and engine is safe to use, practical and efficient.

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Victa 2-Stroke Engine Block – Manufacturing Engineering

Diagrams: Front View

Side View

Top View

Isometric View

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Victa 2-Stroke Engine Block – Manufacturing Engineering

Material Selection: In all designs, there are many factors which contribute to deciding which type of materials to use, the dimensions of the parts in the design. In addition, the process is also important. Both the process and type of material work conjointly to provide the most efficient design. If the right materials are chosen and the correct processes are used, the design, in this case the engine block will be able to withstand heat and pressure and can also resist wear for as long as possible. In terms of the engine block, the materials used are an extremely important choice. If the wrong material is used it can lead to damage to the engine and can even be dangerous since combustion will need to take place within the engine. Generally, when choosing the materials for an engine whether 2-stroke or 4-stroke, there a few main properties that need to be considered. These include: 1. The that should be lightweight in order to be practical. If the engine block is heavy it will limit its applications or reduce the driving force of the machine since the power to weight ratio will be lower. 2. The material must have low thermal expansion. Since combustion is constantly occurring in the engine block, high temperatures will be evident and so the dimensions and sizes of parts of the engine block must stay the same size. 3. The material must also have high strength. Since the engine block is a casing for the process of combustion, the engine will be subjected to high amounts of energy from the combustion and even vibrations from the movement of piston which could eventually wear out the parts and so high strength is needed. Using these 3 main properties, we can conclude that a suitable choice for the manufacturing of engine block would be grey cast iron or an aluminium alloy, specifically A319 and A356. Grey cast iron is an extremely suitable choice for such an application. This is due to a few reasons. Grey cast iron can be casted to form very complicated shapes and designs which is good for engine blocks. Also, grey cast iron is not very expensive and therefore is economically viable especially when engine blocks are common and therefore mass produced. Another good feature of grey cast iron is that it has high vibration damping and is useful in the application of an engine block. Aluminium alloys A319 and A356 are very similar to grey cast iron in terms of their properties. The main difference the aluminium alloys have compared to grey cast iron is the fact that the aluminium alloys are lightweight and therefore can provide a better power to weight ratio. However, the alloys aren’t as strong as grey cast iron and the alloys are more expensive. Considering the fact that the Victa 2-stroke engine will be used on lawnmower, the weight of the engine isn’t the main priority in the design while the price of the manufacturing

process is important. Furthermore, since the engine will be used in lawnmowers, where it is possible to use diesel fuel which creates more vibration, a material with high strength should be used and since grey cast iron has this feature including high vibration damping, it would make a more suitable material.

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Victa 2-Stroke Engine Block – Manufacturing Engineering

Manufacturing:

The manufacturing process I recommend being used when creating the Victa 2-stroke engine block is sand casting. The reasons for this choice is that sand casting is cheaper than die casting. When being used to create engine blocks that will be used for a lawnmower, the cheapest options are the most appropriate. The sand casting process is comprised of 3 main steps which outline the guide to the complete process and a guide to each step. 1. Mold making – the first step in the sand casting process is the creation of the actual mold. The mold is where the liquid metal will sit to form the product. Simply put, two open boxes are filled with sand. A replica of the product is created split into two halves. One half of the replica is placed into one box and the other half is placed in the other box. The replica halves are placed in a way so that when they are joined together they form the complete replica. In this case, green sand (a mixture of water, silica and clay), is used since it is inexpensive and can easily be reused. The sand is then poured into both boxes covering the half molds and it eventually hardens. The boxes are then turned over and the replicas are removed, and the cavities are placed together to form one large cavity. 2. Casting – the casting stage is comprised of three sub-steps. The first step in this stage is to secure the two boxes together so that the product is accurate and forms exactly to the shape of the molds with no excess edges, etc. The boxes are clamped securely in place and the liquid metal is poured in through an opening which leads to the mold cavity. The liquid is then left to cool down and harden. 3. Removal – in this stage, the boxes are separated leaving the mold inside. The mold is removed, and the sand is cleaned off. When the product is removed, there is also hardened metal formed following the path of where the liquid was poured in. this is trimmed off and cleaned and most likely re-melted to be used in the process again. After the product has been removed and excess metal is trimmed, it can be polished and cleaned and smaller details can be added. In this process there are not many materials needed. The main materials needed for sand casting is the sand itself, the molten metal and the crates where the sand will sit. The sand recommended for this process is green sand since it is cheap and can be reused as mentioned above. Also, a lubricant may be used so that the final mold is easy to remove from the sand and crates. The molten metal that we had chosen is grey cast iron and so therefore in this case molten iron would be used as the metal. The crates are the final material in the sand casting process. These are usually made of wood or metals such as aluminium. In relation to the complete process of creating the engine block, machines such as milling machines to add the extra detail which cannot be obtained in the sand casting process. An alternative to sand casting would be die casting. This method is very similar to sand casting with a few differences. Die casting does not use any sand but rather a permanent ‘shell’ made of a metal such as aluminium to create the mold. Die casting offers several advantages over sand casting. Die casting can produce more molds in a given amount of time compared to sand casting. Die casting does not use sand or crates but rather a ‘shell’ to house the mold which saves space. Also, die casting creates molds with a better finish and is more 5...