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Engine Maintenance. Chapter 1 What Makes the Boat Go. Objectives for the Student. Have a good grasp of the components of the modern marine propulsion system Have an understanding of the principles of the modern marine engine, both two stroke and four stroke
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Engine Maintenance Chapter 1 What Makes the Boat Go
Objectives for the Student • Have a good grasp of the components of the modern marine propulsion system • Have an understanding of the principles of the modern marine engine, both two stroke and four stroke • Have an understanding of the general troubleshooting methodologies that can be used and repair work that needs to be done
The Marine Engine • Needed for combustion: • fuel • air (oxygen) • ignition source
The Marine Engine • A compressed fuel/air mixture is ignited • Burning mixture increases in temperature and pressure • Expansion of gas is converted to linear piston motion • Crank converts linear motion to rotary motion
Intake fuel/air enters the combustion chamber The Marine Engine
Compression mixture is compressed within the cylinder The Marine Engine
Power compressed charge is ignited to move the piston downward The Marine Engine
Exhaust spent gases are expelled The Marine Engine
The Diesel Engine • Intake • air enters the combustion chamber
The Diesel Engine • Compression • air is compressed to high temperature
The Diesel Engine • Power • fuel is injected and autoignites
The Diesel Engine • Exhaust • the spent gases are expelled
Displacement • Cylinder Displacement • The total volume of air that can be moved in one engine cycle for one cylinder • Bore • Diameter of the cylinder • Stroke • Total piston travel from TDC to BDC
r h Displacement • Volume of a Right Circular Cylinder • V = p r2 h • where • V = volume • p = 3.1416 • r = radius (1/2 diameter) of cylinder • h = height of the cylinder (stroke)
Displacement • Engine Displacement • The total volume of one cylinder’s displacement, times the number of cylinders • Displacement = n V = n p r2 h • where • n = number of cylinders • V = volume of one cylinder
Displacement • Example: Chevrolet 350 V-8 • Bore = 4.00 inches • Stroke = 3.48 inches • Displacement = n V = n p r2 h • Displacement = 8 x 3.1416 x (2.00 inches)2 x 3.48 inches • Displacement = 350 inches3 or 350 cubic inches or 350 cubic inches displacement or 350 CID
Size Matters • Engines of Greater Displacement Generally Deliver More Horsepower • More fuel/air consumed per stroke • More heat released • More power produced
Engine Compression • Compression Ratio • The cylinder’s total volume at BDC, divided by volume at TDC • Compression Ratio = V / v • where • V = volume at BDC • BDC = bottom dead center • v = volume at TDC • TDC = top dead center
Engine Compression • Compression Ratio = V / v • V = 17 cubic inches • v = 2 cubic inches • V / v = 17/2 = 8.5:1
Horsepower and Torque • Horsepower • measure of work per unit of time • 1 hp = 745 watts • Torque • measure of rotational force • pounds-foot (lb-ft) • Newton-meter (Nm)
The Marine Drive System • Three Basic Types of Marine Drives: • Outboard • Inboard • Stern Drive, also known as Inboard/Outboard or I/O drive
The Marine Drive SystemOutboard Systems Power Head Intermediate Housing Lower Unit
Thrust Units • Propeller • 2-4 blade (inboards) • 3-6 blades (outboards) • Pitch • measure of advance (one rotation through a solid object) • Diameter • diameter of a circle that describes the blade tips
Thrust Units • Water Jet • Internal impeller • Good for shallow water operation • Directs thrust using steerable nozzle and reverse gate
General Troubleshooting Methodology • Check the Obvious • Check the Easy • Check Systematically • Make No Erratic Adjustments
Remember… You should be able to identify problems and explain them to a mechanic