Purpose: To understand the four-cycle internal combustion engine
Background and reference materials:
Briggs & Stratton Service and Repair Instructions, Briggs &
Stratton Corporation, Milwaukee, WI, 1992
Physical principles involved: Bernoulli's principle, 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
Manufacturing processes introduced: casting, machining, molding
Activities: dissection, sketching, dimensioned drawing of the piston, calculating engine displacement
Associated Lecture Material: (engine.ppt) engine types, history, theory of operation
Required tools: basic toolbox, parts bin, calipers, starter clutch
wrench (E), flywheel wrench set (C), ring expander (B), ring compressor (D),
valve spring compressor (A), torque wrench
Deliverables:
Session 0: Getting the Patient Ready
Readings: Briggs and Stratton Repair and Service Manual
Objectives:
Activities and questions:
1. Note the manufacturer, model, and serial number of your engine
2. What is the maximum RPM for this engine
3. How much torque and horsepower does it develop
4. Check that there is no fuel and oil in the engine
5. Determine if the engine has compression
6. Check to see if ignition system is functioning
7. Explain the four cycles (in your journal)
8. Draw an overall diagram of your engine (external view of assembled engine), label all important parts
Session 1: Ignition and Carburetor
Readings:
Objectives:
Procedure:
A. Ignition System
1. Remove the flywheel shroud
2. Identify the type of ignition system your engine uses
3. What materials are used in the flywheel?
4. Remove the flywheel using the proper tools
5. What is the purpose of the starter clutch? Notice how it does not work in some orientations.
6. How much does the flywheel weigh and what is its function? What would be
the advantages and disadvantages of making it heavier?
7. Why does the flywheel have one section made from a different material?
8. Sketch the ignition system identifying all its components
9. Describe how the magneto system works
10. What is ignition timing and why is it important?
11. Remove the rest of the ignition system components
B. Carburetor
1. Remove the air cleaner and identify the type used
2. Why is the air cleaner important?
3. Identify the carburetor style (pages 4 - 5 Section 3)
4. Remove the carburetor
5. What materials are used in the carburetor?
6. Describe how the venturi works.
7. How many jets are used and what is their function?
8. How does the choke work?
9. What type of governor system does this carburetor use? How does it work?
10. Completely dissect the carburetor assembly
11. Sketch the components of the carburetor
12. Reassemble and adjust the carburetor according to the factory
specifications
Note: Do not re-mount the carburetor to the engine block, this is to be done in the last engine dissection lab!
Session 2: Engine Block Dissection
Readings:
Objectives:
Procedure:
1. Remove the cylinder head
2. Are all the bolts the same length? If not explain why and note their
location
3. Locate the intake and exhaust valves. Which one is larger and why?
4. Sketch the top view of the cylinder (include the valves)
5. Rotate the engine through its four cycles. Note what happens if you turn it the wrong way
6. Calculate the displacement of the engine _______ cubic inches = ________ cc's
7. Determine the compression ratio and explain how it was found.
8. Remove the valves (use your safety glasses!!)
9. Is one valve spring longer than the other ? if so, why ?
10. Remove the crankcase cover, being careful not to damage the gasket. (do not
pry off with a screwdriver, it will tear!)
11. Remove the camshaft and crankshaft.
12. What materials are used for the camshaft?
13. What is the significance of cam timing and how is it set?
14. What are tappets and what function do they serve?
15. What type of lubrication system does your engine have and how does it work?
16. Sketch the camshaft assembly
17. Remove the piston
18. Measure and sketch the piston assembly. Produce a fully dimensioned 2-D
CAD drawing of the piston, making all necessary physical measurements.
19. Remove the rings (using the ring expander) and identify them
20. Remove the wrist pin and connecting rod
21. What manufacturing processes do you think are used to produce the
crankshaft, camshaft, connecting rod, wrist pin, and piston?
22. Remove the crankshaft. What type of bearings does it use?
23. What material is used for the crankshaft?
This completes the engine dis-assembly
Session 3: Reassemble
Readings:
Objectives:
Procedure:
Note: Use small amounts of engine oil to lubricate mating parts (bearings, rings etc.). The service manual must be followed during reassembly.
1. Reassemble your engine. Install parts in the reverse order which you disassembled them (this is a test of your memory, journal completeness, and common sense).
2. Use the ring compressor
3. Torque all bolts to the factory specification Write in the
required torque values (and the correct units!) here:
Crank bolts: _________ Head Bolts: _________
Flywheel: _________
4. What grade bolts are used for the connecting rod?
5. Why is it important to torque the bolts to a certain value? How is this value determined?
6. Why are the bolts torqued in a certain pattern?
7. What is the purpose of the head gasket?
8. Prepare to run you engine!
9. Fill the engine with oil and gas (only enough gas to run the engine for a minute or two)
10. While it is running you should adjust the air/fuel mixture, idle speed, and
governor speed. Know these procedures before you start!
11. After running the engines, the fuel and oil must be drained. (Let the
engine cool first.)
12. What happened when you changed the air fuel mixture?
13. Did your engine operate smoothly? If not, you must make whatever
adjustments are needed to satisfy the instructor that the engine is running properly.
Engine Dissection Feedback:
Please comment on this lab experience. Fill out this form and submit it to the instructor within one week of the completion of the dissection exercise.
Your Major __________________ Semester Standing __________________
C. How would you rate the difficulty of this dissection? Trivial About right Too difficult 1 2 3 4 5 B. How would you rate the overall value of the this dissection as a learning experience? Worthless Mediocre OK Good Excellent 1 2 3 4 5 D. How could the learning experience be improved?
Notes to Instructors
Format for lab: 2 persons per group is best (3 is OK if necessary)
Total time for dissection: Four periods, 2 hours each
Associated lecture material: (2 or 3 fifty minute lectures)
4 stroke engine fundamentals (engine.ppt)
"Why internal combustion engines" - discussion of Invention and Technology article
Facilities needed: Workbenches (each group needs a bench approximately 4 x 6 feet)
Supplies needed: (available from any small engine repair shop)
General Purpose Tools - socket wrenches (1/4" and 3/8" drive), screw drivers,
pliers, nut drivers, etc. (need both English and metric sizes for Briggs
engines)
Safety glasses
Torque wrench (1/4 or 3/8" drive, max torque needed is 140 in-lbs)
Vernier caliper
Shop rags
Hand cleaner
Funnel
Oil pan
Clear contact paper - to cover and protect the Briggs and Stratton repair
manual
Gasoline, 30W oIl
Engine mount- a plywood board with 1/4" bolts is fine, C-clamp to a rigid
base
Exhaust tubing - to duct exhaust out a window or vent if running engines inside
(but its better to run them outside)
Total cost: