THE CONSTRUCTION OF DIESEL ENGINES

e [Music] the engine frame is the main strength member of the diesel engine every part of the engine depends upon this frame for support combustion takes place and power is developed within the cylinders in most modern diesel engines the cylinders consist of three parts the cylinder jacket the cylinder liner And the cylinder head the Pistons convert the pressure of the combustion gases into reciprocating motion a series of piston rings called compression Rings prevents leakage of the combustion gases around the piston and conducts heat to the water cooled cylinder walls oil control Rings distribute lubricating oil over the cylinder walls the reciprocating motion of the Piston is converted into more convenient rotary motion by the connecting rod and the crankshaft the crankshaft is supported in the bed plate by main bearings situated between the cranks linked with the crank shaft is the cam shaft by means of cams the cam shaft actuates the intake and exhaust valves the fuel pumps and the injection valves cam action is transmitted to the valves through the rocker lever assembly on the cylinder head these principles of basic construction apply generally to all types of diesel engines there are however a few exceptions in the two stroke cycle engine the cylinder liner carries intake or scavenge ports which replace the intake valve frequently the exhaust valve also are replaced by ports in the wall of the liner the double- acting engine requires two cylinder heads the lower one has a forged neck with a stuffing box through which the Piston Rod passes the Piston Rod is attached to a cros head which links it to the connecting rod the opposed piston engine has no cylinder head the cylinder jacket and liner are necessarily longer than in the other types the earliest diesel engine frame borrowed from the steam engine was the a frame it derives its name from its resemblance to the letter A the crank case type of construction was introduced with the Advent of the medium and high-speed diesel engines its purpose is to allow for forced lubrication and to reduce the ratio of weight to horsepower in the end block type of construction the entire crankshaft housing and the cylinders are made in one piece this construction is generally limited to the smaller size engines another design developed to save weight is called the stay bolt or tie rod type here the cylinders are secured with long rods to the bed plate the modern engine however is usually a combination of these construction part of the frame the cylinder jacket is the main strength member of the cylinder it made of cast Steel in some older engines the cylinder is formed by the inner surface of the jacket in this case passages for cooling water are contained within the wall of the jacket usually however the modern engine has a separate cylinder liner if this is not in direct contact with the cooling water it is called a dry liner in most large engines the liner is directly in contact with the water this type is called the wet liner the cylinder liner is cast with a shoulder upon which it rests in the jacket the liner is a tube of close grained cast iron or steel with a finely polished accurately dimensioned inner surface in the two-stroke cycle engine intake ports and sometimes exhaust ports are cut into the wall of the liner in the opposed piston engine the liner is lengthened to accommodate the additional piston and is drilled at the center for fuel injection air starting and cylinder test and relief valves in fourstroke cycle engines the intake and exhaust and the fuel injection valve are carried in the cylinder head this is ordinarily made of cast iron and is formed with spaces for the cooling water piston Crown shapes are many and varied the crown may be convex or concave or of a special design to increase air turbulence thus raising combustion efficiency Pistons are made of cast iron or of cast or forged steel sometimes aluminum alloy Pistons are used to save weight and facility cooling the top surface of the Piston is called the crown the lower part is the skirt the underside of the Piston is often cast with a series of ribs to increase rigidity and promote cooling the Piston pin held by bosses in the Piston walls upper pivot of the connecting rod this piston is of the trunk type in the double acting engine the Piston is of the cros head type it is fitted to a piston Rod which is in turn secured to the cros Head the Piston is made in three sections a central section to allow for expansion and two piston heads which carry the piston rings passages for the circulation of cooling oil are contained within the body of the piston in the double acting engine to allow for heat expansion piston diameters are always several thousands of an inch smaller than the cylinder bore piston rings are therefore needed to seal the combustion space against es scape of the gases around the Piston there are two major types of piston rings compression rings to seal the combustion space and oil rings to assist in controlling the lubrication of the cylinder walls both types conduct heat from the Piston to the cylinder walls piston rings are made of cast iron forged steel or special Alloys when made of of iron they are sometimes backed by a steel band for increased strength and tension or they may be equipped with a bronze strip run in the bearing surface to hasten the wearing in of the Ring The Ring joint may be straight or square cut or angle cut to reduce blowby of combustion gases offset joints such as square step cut or round step cut are often used oil control rings have two functions to distribute oil evenly over the cylinder walls and to remove excess oil which is returned to the crank case the upper Edge is always beveled and the lower Edge is generally Square the connecting rod is made from a highgrade steel forging this newer type with an I beam cross-section is both lighter and stronger than the circular section rod used on the older engines in the usual Rod Construction the Piston end is forged with an i for insertion of the Piston pin bearing the crankshaft end which carries the crank pin bearing is made in two parts the cap is fastened to the rod by bolts and cap nuts the rod is rifle drilled from end to end this provides a passage for the flow of lubricating oil to the Piston pin bearing in large general motor submarine diesel engines an oil spray nozzle is attached to the upper end of the rod cooling oil is sprayed through this nozzle onto the underside of the Piston head in the double acting engine the connecting rod has a forked end which straddles the cros head to which the Piston Rod is secured the crankshaft is generally made of special forged steel carefully heat treated for stress relief and balanced both statically and dynamically to reduce vibration the crankshaft is comprised of main bearing journals crank webs and crank pin journals the crank pin and main bearing journals are accurately machined to provide smooth bearing surfaces in small high-speed engines the crankshaft is usually of integral construction cast or forged from a single piece of Steel large crankshafts may be of builtup construction with the main journals and crank pins pressed into the webs or they may be made by a combination of the two methods in all forced lubrication engines the main journals in crank pins are drilled for the passage of lubricating oil to the bearings and connecting rods in the inline engine there is a separate crank for each cylinder in the vtype engine however there is ordinarily one crank for each pair of opposite cylinders the two connecting rods operating on a single crank pin Journal the crank angles vary with the number of cylinders in the engine cycle thus the power impulses of the Pistons are always evenly distributed over the full revolution of the crank shaft bearings are made in halves the bearing metal being carried in separate shells or in the bearing support and cap bearings may be adjusted to the proper fit by scraping or by the use of shims Precision type bearings commonly used in modern engines are accurately machined to the proper dimensions and require no further fitting bearings of the roller bearing type have the advantages of reduced friction and longer life but are difficult to install they are mainly used to transmit heavy loads or very high speeds the cam shaft is made of high-grade steel the specially hardened cams are either forged integral or they are made separately and keyed and shrunk to the shaft the cams actuate the valves pump plungers and other units at the proper intervals in the engine cycle thus the cam shaft directly controls the timing of the engine it is driven from the crankshaft by gearing or a chain The Rocker lever assembly is ordinarily located on top of the cylinder head its purpose is to transmit cam action to the the valves and the fuel pump plungers the parts of a typical rocker lever assembly are The Rocker lever or arm the cam follower the push rod and a supporting pedestal and shaft engines without intake and exhaust valves do not require rocker lever assemblies except in some cases for fuel pumps and injectors basically all diesel engines are constructed alike though their parts may be made and assembled in many different ways the same fundamental principles of construction apply to all diesels from the simplest to the most complex