2. Top of the Piston. Various shapes aid in creating air turbulence for combustion Confines each ring used to seal the space between the cylinder wall and piston Crown Ring Grooves Ring Lands Skirt Bosses Part of the piston above the top ring or between the ring grooves. Limit and support the piston rings in their grooves. Oil Drain Passages Permit oil to pass through the piston from the cylinder wall into the crankcase. Part of the piston between the the first ring groove above the piston pin hole, and the bottom of the piston. Reinforced openings in the piston body. Provide a means to connect the piston to the connecting rod.
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Editor's Notes
Diesel Construction Moving Components Piston -The cylindrical device which forms the moving end of the cylinder. All power produced by the engine is transmitted as pressure applied to the working face of each piston.
Diesel Construction Moving Components Crown - Top of the Piston. - Various shapes to aid in creating air turbulence for combustion Ring Grooves - Confines each ring used to seal the space between the cylinder wall and piston Ring Lands - Part of the piston above the top ring or between the ring grooves. Limit and support the piston rings in their grooves. Skirt - Part of the piston between the the first ring groove above the piston pin hole, and the bottom of the piston. Bosses - Reinforced openings in the piston body. Provide a means to connect the piston to the connecting rod. Oil Drain Passages -Permit oil to pass through the piston from the cylinder wall into the crankcase.
Diesel Construction Moving Components Trunk Type - Unit construction -Skirt is long enough to take up side thrust without scoring (scratching) the liner.
Diesel Construction Moving Components Piston Oil Cooling - Heat absorbed by the piston must be dissipated to prevent excessive metal temperature, and the carbonization of lubricating oils. -Piston Cooling Methods
Diesel Construction Moving Components Piston Rings -Seal the cylinder. -Prevent combustion pressure from entering the crankcase (blow-by). -Prevent oil from entering the combustion space. -Distribute oil to lubricate the cylinder walls. -Transfer heat from the piston to the cylinder walls.
Diesel Construction Moving Components Oil Rings -Used for distribution, removal of excess oil, and control of oil film. Note: Different manufacturers use a variety of terms in their Tech. Manuals to identify the oil rings, such as oil control, oil scraper, oil wiper, oil cutter, oil drain, oil regulating. -Furthest from the combustion chamber, Regulate the amount of oil passing between the skirt and cylinder wall. -Preventing excessive oil from entering the combustion chamber.
Diesel Construction Moving Components Piston Pins/Wrist Pins - Usually hollow and made of alloy steel. -Machined, hardened, precision ground and lapped. -Some may be chrome plated to improve wearing properties. Purpose: Connect the piston to the connecting rod. Location: Ride on a carrier or boss inside the piston
Diesel Construction Moving Components Connecting Rod - A bar or strut with a bearing at each end. -Usually forged from alloy steel. -I or H section to give it greater strength for its weight. -Upper end is attached to the piston by the piston pin. -Lower end is split so it can be fastened around the crankshaft
Diesel Construction Moving Components Crankshaft -Forged steel with design determining the firing order for a given direction of rotation
Diesel Construction Moving Components Construction - Connecting rod journals -Offset from the crankshaft centerline -Orbit the centerline as shaft rotates Crank Journals (Main Bearing Journals) -Induction hardened for durability and wear. -Machined to a highly polished finish -Mounted to the block by main bearing caps Crank Throw -3 parts- 2 webs and a pin -Provide attachment points for the connecting rods
Diesel Construction Moving Components Single cylinder engines require large flywheels to keep speed variations within limits. Multi-cylinder speed variations become less as the number of cylinders increases. -Cylinders are smaller and impulses more frequent. -Ends of the connecting rods, crank webs and crankpins have considerable weight and therefore have the same inertial effect as the flywheel. -Some engines the rotor of the generator serves as the flywheel.
Diesel Construction Moving Components Valve Assemblies -Intake and exhaust valves are “Poppet Type” -Purpose- On 4 cycle engines the valves open and close to allow clean air to enter the cylinder and allow the exhaust of spent gases. -Some 4 cycle engines use 2 intake and 2 exhaust valves per cylinder. -2 cycle engines may have intake ports and exhaust valves or may have both intake and exhaust ports. -2 cycle engines using exhaust valves generally employ 2 or 4 valves per cylinder. Location - Valves are located in the cylinder head assemblies.
Diesel Construction Moving Components Sodium valves are effective but not commonly used. -Sodium can be highly explosive when it comes in contact with the atmosphere. -Seating edge of the face may be 30,45 or 60 degrees. -Seating angles are required to provide a positive seal. -Over half the heat a valve must dissipate, leaves through the valve face. -Face and seat surfaces may be hardened with a cobalt-tungsten alloy to resist thermal damage.
Diesel Construction Moving Components Valve Guides Purpose Provide a guide and bearing for the valve stems. Also aid in conducting heat from the stem to the water jacket which surrounds the guide. Location Pressed into the cylinder head Valve rotators: ( not found on all engines.) Purpose Rotate the valve, preventing carbon buildup and hot spots that could damage the valve and seating surfaces. Location May be installed above or below the valve spring, according to design requirements.
Diesel Construction Moving Components Valve Actuating Mechanism -Used to control the opening and closing of valves and fuel pumps/injectors -Camshaft: A long slender shaft with a number of projections called cam lobes. -The timing desired determines the shape of the lobes. -Lobes are elliptical so the valves are opened and closed gradually to avoid excessive inertial forces. May be located low near the crankshaft, on the cylinder block or in/on the cylinder head.
Diesel Construction Moving Components Timing -Camshafts time the events of the intake, compression, injection, power and exhaust to the crankshaft. -Therefore the connecting drive must be positive, i.e. gear, chain or cogged belt drive.
Diesel Construction Moving Components Push rods Purpose : Transmit the motion of the cam and lifter to the rocker on the cylinder head. Location : Between the cam followers and the rocker arms.
Diesel Construction Moving Components Bearings -Make up a very important group of parts. Functions Support rotating shafts and other moving parts Transmits load from one part to another. Reduce friction between moving surfaces. Dissipate heat produced by friction
Diesel Construction Moving Components Classification by construction -Precision type -Requires no fitting to the shaft. -May be split inserts which form a bushing when put together -May be of solid construction.
Diesel Construction Moving Components Drive Mechanisms Identifies the group of parts which take power from the crankshaft and transmits that power to various engine components and accessories . -Camshafts -Pumps -Blowers The drive mechanism does not change type of motion but it may change direction of motion
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