Purpose: To learn more about the design and operation of the four-cycle internal combustion engine
Acknowledgment: This module uses as its inspiration, materials from ME/IE 497: Product Dissection, a one semester course at Penn. State University developed by John Lamancusa under the Manufacturing Engineering Education Partnership.
Background and reference materials: Briggs and Stratton Service and Repair Instructions, Briggs and Stratton Corporation, Milwaukee, WI, 1992.
Physical Principles involved: Bernoulli's principles, combustion, magnetic fields and induction, static and dynamic forces, heat transfer.
Mechanisms involved: carburetor, flywheel, magneto, journal bearings, crank-slider (piston, connecting rod, crank shaft), cams, valves, fasteners
Manufacturing processes introduced: casting, machining
Activities: dissection, sketching, calculations (engine displacement, thermal strains, etc.)
Required Tools: basic tool box, parts bin, torque wrench, specialty tools (a: valve spring compressor; b: piston ring expander; c: flywheel holder; d: piston ring compressor; e: flywheel remover)
Deliverables:
Schedule:
Objectives:
A: Tool Inventory 1. Count and record all tools in your tool box. 2. Turn in your tool inventory to your instructor. B: Preparation 3. Note the manufacturer, model, and serial number of your engine. 4. What is the maximum RPM for this engine? 5. How much torque and horsepower can it develop? 6. Check that there is no fuel in the engine. 7. Determine if the engine has compression. 8. Explain the four cycles in your journal (use sketches in your description). 9. Draw a simple diagram of your engine, label all important parts. 10. How does the cooling system work for this engine? C: Start and test engine 11. Mount the engine to the aluminum plate provided. (already done) 12. Fill the oil reservoir with oil and pull the starter handle slowly to lubricate the engine. Make sure there is no gas in the fuel tank. 13. Take your engine outside, fill the gas tank with gas and secure it to the cart. 14. Start your engine. Adjust the throttle and let the engine run for no more than one (1) minute - if the engine gets too hot it will be difficult to dissect. 15. Turn off the engine. 16. Record any observations about your engine's performance in your journal. 17. Allow the engine to cool for a couple of minutes. 18. Remove all of the gasoline from the fuel tank. Do not bring any engines into the lab with gasoline in them. D: Start Disassembly, if you have time Engine Dissection - Sessions 2 and 3: Disassembly, How it works Objectives: a) Disassemble the engine b) Understand how the different systems of the engine work Disassemble Guidelines and Tips: 1. Read the repair manual before you remove a part (e.g. the flywheel). 2. Make notes and sketches to ensure that you can reassemble all of the parts easily. Record the exact method you used to disassemble your engine (i.e. the order in which the parts were removed, etc.) 3. Use nut drivers to remove all bolts. 4. When you remove a bolt, instead of just throwing it in your parts bin, thread it back into the place where it came from (after the mating part has been removed !). For example, after you remove the carburetor, screw the two mounting bolts back into the engine block. 5. Be extremely careful with the gaskets - we may be able to reuse them (although this is not generally a very good idea). 6. Make sure you note where the timing mark meshes with the gear on the cam shaft. You may have to use a pen. If you are not sure where the timing mark is, ASK! 7. The following disassembly order has been successful in the past: flywheel shroud air vane (plastic piece on the side of the armature) armature and wind vane bracket armature wires armature grounding wire carburetor assembly. muffler (use special tool [a spanner] available from the lab instructor) side shroud cylinder shroud mesh screen on flywheel flywheel nut flywheel crank case cover - drain oil first and beware of sharp edges spark plug - use spark plug socket head After removing the head: 1. Reassemble and rotate the flywheel. 2. Record your observations. 3. Disassemble the flywheel. valve spring cover (on side of engine with vertical tube attached) valve springs valves cam shaft connecting rod (optional - talk to instructor first) piston (optional) Understanding How the Engine Works: As you disassemble your engine, complete the following steps and questions according to the following guidelines:. Complete the steps and answer the questions that have an asterisk (*). The steps with an oΉ are optional. Talk with your instructor if you wish to complete any of these steps. Do not complete the steps that have neither an *Ή nor an ³o². A. Ignition * 1. Identify the type of ignition system your engine uses. * 2. What types of materials are used on the flywheel? Why does the flywheel have one section made from a different material? * 3. What is the purpose of the flywheel? How much does it weigh? What would be the advantages and disadvantages of making it heavier? * 4. What is the purpose of the starter clutch? o 5. What is ignition timing, and why is it important? How is timing achieved in your engine? B. Carburetor * 7. What type of air cleaner is used on your engine? Why is the air cleaner needed? 8. Identify the carburetor style (pp. 4-5, Section 3 of the Repair Manual), and sketch the carburetor components. 9. How many jets are used and what is their function? * 10. How does the choke work? * 11. What is the function of the governor? 12. Completely dissect the carburetor assembly. DonΉt even think about it! 13. Sketch the components of the carburetor. 14. Reassemble and adjust the carburetor according to factory specifications. Do not remount the carburetor to the engine block - this is to be done in the last engine dissection lab. C. Engine Block, Valves, Crankshaft, Camshaft, Pistons, etc. * 15. Locate the intake and exhaust valves. Which one is larger? Why? 16. Measure the margin. Is it with factory specifications? (see Theories of Operation) 17. Which valve has a special valve guide? Why? * 18. Explain what happens in the valve spring compartment. * 19. Why is the cam shaft made of nylon? * 20. What is the significance of cam timing, and how is it set? * 21. What is the relationship between the cam timing and the flywheel magnet? * 22. Sketch the camshaft assembly. * 23. What are tappets? o 24. Sketch the piston assembly. o 25. What type of bearings does the crankshaft use? 26. What grade bolts are used for the connecting rod? Engine Dissection - Sessions 4 and 5: complete reassembly and testing Objectives: a) Completely reassemble the engine b) Better understand how the engine works c) Start and adjust the engine d) Complete final checkout Note: 1. Use small amounts of engine oil to lubricate mating parts (bearings, valves, etc.). 2. The service manual must be followed during reassembly. 3. Before you reassemble your engine, tell the lab instructor if you have any broken parts or torn gaskets. A. Completely reassemble the engine * 1. Reassemble your engine (except for the head). Install parts in the reverse order which you disassembled them (this is a test of your memory, journal completeness, and common sense). * 2. Be sure to use a torque wrench when it is recommended - i.e. rod cover [optional disassembly part], crank case cover, flywheel and head. Torque all bolts to the factory specification. Is a 100 Lb-in force a large force? Finger tighten Bolts before using the torque. Do not over-tighten any of the bolts - remember, the engine block is aluminum, and the threads can get stripped very easily. * 3. Use the ring compressor to reassemble the piston cover [optional disassembly part] * 4. What is the bore of your engine? What is the stroke? Compute the displacement. What does the displacement indicate? * 5. Install the head and remaining parts. * 6. Why is it important to torque the bolts to a certain value? How is this value determined? * 7. Why are the bolts torque in a certain pattern? * 8. What is the purpose of the head gasket? * 9. Prepare to run your engine! B. Run, adjust and test the engine 10. Describe how to adjust the air/fuel mixture. idle speed, and governor speed. * 11. Fill the engine with oil, and then take it outside. * 12. Fill the engine with gas. Start the engine. o 13. While it is running you should adjust the air/fuel mixture, idle speed, and governor speed. Know these procedures before you start! 14. What happened when you changed the air fuel mixture? 15. Did your engine operate smoothly? * 16. Let your engine cool. * 17. Drain the fuel. C. Final checkout * 18. Clean your tools * 19. Inventory your tools If you know of any missing tools, find them. If you have extra tools, find out where they belong. Organize the sockets in your box. * 20. Return your tool box to the lab instructor for final inspection.