Engineering Training

ASSIGNMENT SHEET

DIESEL ENGINE CONSTRUCTION

Assignment Sheet Number 2.2

INTRODUCTION

--Diesel engine construction will cover all engine components and their interaction as a basis for a thorough understanding of emergency diesel generator design and operations. Throughout the lesson reference will be made to the specific design of components found on the Fairbanks Morse 38ND8-1/8 (CGN) and General Motors 16-645E5N LL (CVN) diesels.

LESSON TOPIC LEARNING OBJECTIVES

Terminal Objective:

--2.0 Supervise the operation and maintenance of CVN and CGN emergency diesel generators. (JTI:B)

Enabling Objectives:

--2.3 Describe the construction of the following diesel engine components:

a. Crankshaft assembly

b. Cylinder block

c. Cylinder head assembly

d. Piston assembly

2.4 Describe the function of the following diesel engine components:

a. Crankshaft assembly

b. Cylinder block

c. Cylinder head assembly

d. Piston assembly

2.5 Describe the operation of the following diesel engine components:

a. Crankshaft assembly

b. Cylinder block

c. Cylinder head assembly

d. Piston assembly

STUDY ASSIGNMENT

1. Read Information Sheet 2.2

2. Outline Information Sheet 2.2 using the enabling objectives for lesson 2.2 as a guide.

3. Answer study questions.

STUDY QUESTIONS

1. How does oil cool the underside of the piston?

2. What are the two types of lube oil sumps?

3. What are the three different types of cylinder liners?

4. How does the exhaust and intake valves operate?

INFORMATION SHEET

DIESEL ENGINE CONSTRUCTION

Information Sheet Number 2.2

INTRODUCTION

REFERENCES

(a) NAVEDTRA 10539, Engineman 3

(b) NAVEDTRA 12149, Engineman 2

INFORMATION

.Both CVNs and CGNs use diesel engines extensively. The main use of diesels is for Emergency Diesel Generators (EDGs). Diesels can also be found in all the small boats on board. Although the propulsion diesels found in the small boats are much smaller than the behemoths used in the EDGs, they still operate on the same basic principle and have many of the same parts.

. CVN - There are 4 General Motors 16-645E5N LL engines powering 4 2000 KW generators. Two engines are in the forward part of the ship and two are in the aft. All of the EDGs run on JP-5. The diesels are operated and maintained by RA division consisting of Enginemen.

. CGN - There are 2 Fairbanks Morse 38ND8-1/8 engines powering 2 1000 KW generators. One is in the forward part of the ship and the other is in the aft part. Both of the EDGs run on JP-5. The diesels are operated and maintained by A division consisting of Enginemen.

.Engine frame - Houses all the moving parts of the diesel engine The engine frame provides a mounting surfaces for accessories, storage for the lubricating oil, passages for lube oil, jacket water, air and fuel oil, and also provides a mounting surface for fuel, air, lube oil, and jacket water lines.

. Cylinder block - The cylinder block is a portion of the frame, that supports the cylinder liners and heads and sometimes will include the crankcase. The cylinder block supports the crankshaft, camshaft, and passages for lube oil, fuel, air, and jacket water cooling, or these passages will be attached to the block.

--. En-bloc construction - Used for most small high speed diesel engines, where the blocks are a cast one piece design to include the crankcase. Jacket water, lube oil, and air passages are integrally cast with the engine block. Most En-bloc engines use an oil pan for the storage of lube oil. These types will be found in small boats.

-- . Welded steel plate construction (Fairbanks Morse 38ND8-1/8 and GM 16-645E5N LL) - Used for larger main propulsion engines and diesel generators as this method of construction helps reduce the engine weight. Welded steel plate construction consists of steel plates welded to cast forgings in areas of stress such as main bearings or connecting rod bearings. The passages for lube oil, jacket water, fuel, and air will be attached lines and or will be formed by the steel plates.

. Sumps - The sumps are used as an oil reservoir for lube oil on large diesel engines. They are also the base for mounting the engine block. Sumps will normally have some type of opening called a crankcase cover for access to the crankshaft and bearings. There are two types of sumps:

--. Wet sump - (found on Fairbanks Morse and GM) The oil reservoir is part of the crankcase and base. Oil will return to the sump by gravity flow after it has lubricated the various parts of the diesel engine. In systems of this type, the pressure pump draws oil directly from the sump and recirculates the oil through the filtering equipment and the diesel engine.

-- . Dry sump - The oil is pumped from a catch pan under the crankcase by a lube oil scavenging pump and stored in a separate tank located under the deck plates. The sump may also include the strainer and filter. The scavenging pump will keep the catch pan (dry sump) empty while the engine is running. The oil is drawn from the separate sump/tank and circulated through the engine by the attached gear driven pressure pump. The oil will then return to the catch pan by gravity flow.

. End plates - Used on each end of the block to add strength and rigidity to the block. End plates can also be used for mounting surfaces for gears used to drive the camshafts and accessories. (see fig 2.2-1)

. End plate covers - These covers will provide for mounting surface for gear driven pumps.

. Crankcase evacuation system - Most large diesel engines use a type of crankcase exhaust system that will keep the crankcase under a slight vacuum. The primary purpose of the vacuum is to prevent oil leaks. The secondary purpose is to remove explosive vapors that can possibly build up in the crankcase. Their are four types of crankcase evacuation systems:

--. Air eductor system - Used on ALCOs where an eductor is used to pull a vacuum on the crankcase. The air eductor is powered by the air from the turbo-charger.

-- . Blower system (Fairbanks Morse) - Some 2-stroke cycles use the scavenging air blower to draw a vacuum on the crankcase.

-- . Turbo system (16-645E5N LL) - 4-stroke cycle engines use the intake air to draw a vacuum on the crankcase.

-- . Motor driven crankcase vacuum pump - Used on Colt- Pielstick and some ALCO engines, where a vacuum pump draws vapor from the crankcase through an oil separator. This allows useable oil to return to the engine's sump, and clean air to go to the atmosphere.

-- . Most systems will use some type of an oil separation system to help keep from pulling the oil out of the crankcase.

. Covers - The covers are used to close openings and cover moving parts, such as valve covers that cover the head and valves, and air box covers that enclose air boxes.

--. Some covers on the crankcase will be utilized as an explosion proof cover. In the event of a crankcase explosion, the cover will open to release pressure, then reseat itself under spring pressure. This prevents oxygen from re-entering the crankcase which can cause another explosion or fire.

) No cover can be removed for at least 30 minutes after any type of suspected crankcase explosion.

) The CHENG or Reactor Officer must be notified when you remove any cover after a suspected crankcase explosion (includes the dipstick, also).

) By procedure, fire fighting equipment must be broken out and manned in case a fire breaks out.

--. Inspection covers are provided at key points for inspections.

) Air box covers are removed for inspection of the air box, piston rings, pistons, intake ports, and cylinder liners, for dirt, oil, scratches and wear.

) Crankcase covers can be removed for inspection of the crankshaft, connecting rods and bearings for scratches and wear.

) The valve covers are removed for inspection of valves, injectors, and fuel oil jumper lines.

. Cylinder liner - The cylinder liner is a replaceable bore in which the piston rides. These removable liners provide a way of replacing the bore without having to bore or replace the block. There are two basic types of liners:

--. Dry type liners are used with blocks that have integral water jackets (small diesel engines) where cooling water never comes in contact with the liner. This type will be loosely fitted to the engine block.

-- . There are two types of wet liners:

) Plain wet liner - The water jacket or passages for the cooling water are formed by the engine block and the liner itself. Rubber o-rings at both ends of the liner will provide the seal necessary for the cooling water passages.

) Water jacketed wet type liners (Fairbanks Morse and 16-645E5N LL) - The liners of this design have their own cooling water jacket integrally cast or shrunk fit to the liner. (see fig. 2.2-2)

--. Cylinder liner problem areas

) Cracked, broken and distorted liners are caused by overheating, corrosion, and improper installation. This may cause damage to the piston. Hot spots will often form on liner walls caused by an ineffective jacket water treatment.

) Scoring, scratching and or accelerated wear are caused by poor lubrication, dirt in the oil or intake air.

) Ridges at the top of the liner are formed due to normal wear and should be removed.

. Cylinder heads (GM 16-645E5N LL) - Cover the top of the cylinder, enclosing the combustion space. They are bored with penetrations for fuel injectors and valves. Crab bolt nuts contacting each cylinder head hold it securely to the cylinder head retainer in the crankcase. The head is secured to the cylinder liner by eight equally spaced studs and nuts, and the assembly is firmly held in the crankcase, by the crabs.

--. Correct positioning of the cylinder head is ensured by alignment of the water discharge elbow and its mating hole in the crankcase. The crankcase has built in siphon tubes at the second cylinder from the front on the left bank, and second cylinder from the rear on the right bank to siphon the water discharge manifold when the engine water is drained. The cylinder head is made of high strength cast iron alloy having special design cast passages for water and exhaust gases. Drilled water holes at the bottom of the cylinder head match the water discharge holes in the liner. Exhaust passages in the cylinder head line up with mating elbows in the crankcase, which conduct the exhaust gases through the water manifold to the exhaust manifold.

-- . A well is located in the center of the cylinder head for application of the unit injector. To ensure correct positioning of the injector in the head, a mating hole for the locating dowel on the injector is located in the head. Rocker arms, exhaust valves, valve bridges, valve guides, overspeed trip pawl, fuel injector, and other related items will make up a complete cylinder head assembly.

-- Blow down valves are used for:

) Prelight-off inspections - The engine is turned over with the fuel rack disengaged. Look for water or lube oil coming out of the blow down valves. This possibly indicates a bad cylinder liner or head.

) Trend analysis readings - This is done by attaching a Kiene indicator to the blow down valve while the engine is running so you can take compression readings.

--. Cylinder head problem areas

) Cracks in the cylinder heads can occur anywhere, however they will normally occur in the thin areas of the head (between valves and injector) where a great amount of stress occurs. Overheating, adding cold water to hot engines and improper torquing are the most common reason for cracking the head.

) Distortion - Distortion can be caused by improper torquing of cylinder heads or overheated engines.

) Burning or corrosion can be caused by a blown head gasket or improper head installation.

. Engine mounts - Small boats and some small generators are often mounted on vibration mounts (usually rubber). Most large diesel engines are mounted directly to the ships hull.

.Moving components of the diesel engine - The moving parts of the diesel engine provide for controlling the elements necessary for combustion and the transformation of combustion to mechanical shaft energy. The major moving components are the crankshaft, piston assembly, connecting rod, camshaft, valves, operating gear, flywheel, vibration dampener and various gears.

. Crankshaft - The largest and most important of all the moving components. The crankshaft converts the reciprocating motion of the piston and connecting rod to rotary motion that can be used to drive generators, reduction gears, etc. (see fig. 2.2-3)

--. Fairbanks Morse - The upper and lower crankshafts are designed to transmit the power produced in the cylinders to the vertical drive gears and crankshaft coupling. Thrust bearings are provided next to the vertical drive gears and plain main bearings at each transverse vertical member of the cylinder block. Precision machined bearing surfaces are provided for the main and connecting rod bearings.

-- . The crankshaft sprocket for the timing chain drive is secured to the upper crankshaft at the control end. The air start distributor camshaft is also secured to the control end of the upper crankshaft. At the drive end, the blower drive gear is keyed and also held with a retainer plate to the upper crankshaft. The flexible pump drive gear for driving the governor and attached pumps is secured to the lower crankshaft at the control end.

-- . At the drive end, the crankshaft flexible coupling half is fastened with fitted bolts to a flange on the crankshaft. This flexible coupling delivers the power developed by the engine to the generator. Crankshafts are drilled for lubrication (Fairbanks Morse.) They receive oil from the main lube oil gallery via a jumper line. Oil passes through the main bearing then goes to the connecting rod bearing, then through a drilled passage in the connecting rod to lubricate the piston pin. The oil then passes around the piston pin and is sprayed on the bottom of the piston crown to aid in cooling. Oil gravity drains back to the sump.

-- . GM 16-645E5N LL - The crankshaft is a drop forging of carbon steel material with induction hardened main and crankpin journals. On 16-cylinder engines, the crankshaft is made up of two sections whose flanges are bolted together. Main bearing journals are 7-1/2" in diameter and crankpins 6-1/2". The two crankshaft halves are joined at a flanged connection. Counterweights are provided to give stable operation and all crankshafts are dynamically balanced.

. Connecting rods - The connecting rods (con rods) serve as a link between the crankshaft and the piston. Con rods have an eye at one end and the other end is split (connects to crankshaft). Each end will have some type of a bearing surface. There are two types of con rods used on most Navy diesel engines. (see fig. 2.2-4)

--. Conventional - Used on opposed piston (Fairbanks Morse), in line, and V type engines (when offset). These will be drilled for lube oil to pass through.

. Piston pins (wrist pins) - These are used to connect the piston to the connecting rod. They are normally hollow, to provide maximum strength at a reduced weight.

--. Three types of piston pins

) Full floating - Held in place by piston pin retainers in the piston

) Semi-floating - Are free fit at the boss of the piston and fixed at the connecting rod

) Stationary pins - Are press fit in the boss of the piston and float or move on the connecting rod

.Piston assembly - Absorbs the pressure from combustion and transmits it to the connecting rod. Most diesel engines use a trunk type piston.

. The trunk type piston construction

--. The crown is the head or top of the piston that will receive all the heat of combustion. The crown is slightly tapered to allow for expansion caused by the heat of combustion. The under side of the crown often is ribbed to provide extra strength and increase the cooling area. The top may have different designs for turbulence or to allow for protrusions into the combustion chamber.

-- . The trunk (skirt) receives the side thrust from crankshaft action and keeps the piston in proper alignment in the cylinder. The skirt also has grooves to carry all of the piston rings.

-- . Ring grooves and lands will hold and properly space the piston rings along the skirt of the piston. Some of the lands for the oil control rings have drain holes to the inside of the piston.

-- . The piston boss is the reinforced area where the piston pin will fit to allow the connecting rod and piston to be linked together.

-- . Fairbanks Morse has a trunk type piston.

. Unconventional piston - Some diesel engine manufacturers have designed pistons with different methods of cooling to help reduce the weight of the piston.

--. Cooling chambers - Some pistons may have a cooling chamber that holds oil under the piston crown or circulates oil under the piston crown or circulates oil behind the piston rings. Some cooling chambers will have ribs to aid in cooling.

-- . Composition - To reduce weight and keep strength, ALCO pistons use a cast iron crown bolted to an aluminum trunk.

. Trunion piston (16-645E5N LL) - The crown and skirt ride on a carrier, so the piston can rotate on the carrier thrust washer and is held in place by a snap ring. Most trunion type pistons are cooled by piston cooling pumps.

. Piston rings - Piston rings in diesel engines are very important for engine efficiency. They serve three functions: seal the combustion space, control lubrication of the cylinder walls, and transfer heat. There are two types of piston rings classified by the function that they serve: compression and oil control.

--. Compression rings - Serve two purposes: they seal the combustion space, and transfer heat from the piston to the cylinder liner.

) Most are constructed of cast iron and some may have a special bronze insert to aid in sealing as the rings wear in.

) End cuts vary, some may be square, lap joint, or a diagonal cut.

) The number of rings will vary with design of the engine.

) Compression ring installation

--) Always check the butt clearance before installing.

-- ) Rings should be staggered 180� out of line with the piston boss.

--. Oil control rings - Serves two purposes. They control the lubricants used in lubricating the cylinder liner walls and prevent excessive oil from entering the combustion space. They will also transfer heat from the piston to the cylinder liner.

) These will be made of the same type material as compression rings but may come in as many as three pieces.

) The number of rings and the location of rings will vary with each engine design.

) It is important that the beveled edge of the oil control rings be installed correctly, with the edge pointing down.

--. Problems common to piston rings

) Broken rings are most often caused by improper installation or improper fit.

) Sticking rings are most often caused by operating out of parameter (no load).

) Excessive wear of piston rings is caused by the same type of problems experienced in cylinder wear, dirty oil or intake air, and improper operating temperature.

. GM 16-645E5N LL description

--. Consists of a cast iron alloy piston, four compression rings, and two oil control rings. A trunion type piston carrier is used with the piston assembly to allow the piston to rotate or float during engine operation. The carrier is held in position in the piston by a snap ring inside the piston. The highly polished piston pin is applied in the carrier in contact with the bearing insert, and the assembly is bolted to the upper end of the connecting rod.

-- . Internal parts of the piston are lubricated and cooled by the piston cooling oil. Cooling oil is directed through a drilled passage in the piston carrier, circulates about the piston crown area, and then drains through two holes in the carrier located at the taper.

-- . Pistons are given a phosphate treatment to aid skirt lubrication during engine operation. This process etches the surface and produces a non-metallic, oil absorbent, anti-friction coating that promotes rapid break-in and reduces subsequent wear.

-- . The piston pin is made of steel alloy material, with the outer surface carburized, ground, lapped, and polished to a mirror finish. The pin is mounted at the top of the connecting rod and oscillates in the bearing inserts of the carrier. Two bolts pass through the upper end of the connecting rod and screw into the piston pin.

. Fairbanks Morse 38ND8-1/8 description

--. The pistons have three compression rings, one oil scraper and one oil drain ring. The piston pin is supported in the piston insert. The lubricating oil flows through the rod, around the outer groove in the connecting rod bushing, into the piston crown from where it is discharged. The connecting rod bushing is pressed into the connecting rod eye. The lower connecting rods are four inches longer than the upper connecting rods. The bolts are installed through the rod first on the upper crankshaft, and through the cap first, on the lower crankshaft.

-- . Each connecting rod is attached to the crankshaft with bearing shells. These bearing shells are made of cast aluminum and are dowelled together as one. One half of the shell is dowelled into the connecting rod cap and the other half fits into the connecting rod.

.Camshaft - A shaft with eccentric protrusions driven by the crankshaft to control injector and valve operation through the rocker arm assembly. (see fig. 2.2-5)

. Camshafts are normally a one piece construction, forged low carbon steel alloy. The cams are carbonized for hardness.

. Cams on the camshaft consist of flanks and the nose.

. Problems common to camshafts

--. The main problem is wear of the cams due to lack of lube oil or improper lubrication.

-- . Camshafts may break, but this is not a common occurrence.

. Operating mechanism - The operating mechanism (valve and injector) are designed to convert the rotating motion of the camshaft to reciprocating motion to open and close valves and operate injectors. The mechanisms that will operate the valves and injectors consist of followers, push rods, rocker arms, and valve bridges. (see fig. 2.2-6)

--. Cam followers - Most cam followers are of the rocker type and ride on the camshaft where they transmit the action of the cam to the push rod.

-- . Push rod - A hollow tube that serves as a link between the follower and rocker arm.

-- . Rocker arm - Transmits the push rod movement to the valves and injectors. They are of cast or pressed steel construction and ride on a bushing.

-- . Valve bridge - Used as a link between two valves so that they may be operated simultaneously by the same rocker arm.

. Valves - Are used to control the flow of exhaust gases and intake air on 4-stroke cycle diesels and the flow of exhaust gases on 2-stroke cycle diesel engines (single-acting engines). They also seal the combustion space during the power and compression evolution. The valves are closed by spring tension and opened by camshaft and rocker arm assemblies.

--. Construction - The intake valves are a low carbon steel, while the exhaust valves use chromium steel or steel with a high nickel alloy.

-- . Valves normally have a 35� to 45� angle on their faces.

. Valve guides - Replaceable sleeves in the head in which the valves ride.

. Valve seats - Replaceable inserts which are shrunk to fit into the cylinder head. Most valve seats are ground 1/2� less than the valve to allow for expansion.

. Valve springs - Keeps the valve tightly closed. They must be strong enough to close the valve quickly and keep it closed.

Valve keepers - Lock around the valve stem to keep the valve in place. The keepers and the valves must be replaced as a unit.

. Flywheels - Constructed of cast iron with sufficient weight to limit fluctuations in speed. The flywheel stores up energy during the power event and returns it during remaining events. In doing this, a flywheel:

--. Keeps the variation in speed within desired limits at all loads

-- . Limits the increase and decrease in speed during sudden changes in load

-- . Aids in forcing the piston through the compression event when running at low or idle speeds

-- . Provides leverage or mechanical advantage for a starting motor through a ring gear for starting the engine

. Diesel engine barring gear - The barring gear is installed to turn the engine over by hand for inspection, repairs, timing, and checking the diesel engine for freedom of movement prior to starting.

. Vibration dampeners - It is not always possible to make a crankshaft so rigid that resonance with some of the higher order harmonics of its natural frequency will not occur within the operating range. Therefore, crankshafts are equipped with vibration dampeners to prevent dangerous vibration build up. Normally they are attached to the crankshaft at the end opposite the flywheel. The vibration dampeners are normally either viscous filled or a hydraulic paddle wheel type.

. Gears - Used for the purpose of engine timing between the crankshaft, camshaft, and for driving various engine accessories (pumps, blowers, balance shaft, etc.)

--. Most gears used in diesel engines are made of cast iron and are either spur or helical.

-- . Gears are normally lubricated either by spray nozzles, splash lubrication, or in some cases lube oil returning to the sump may lubricate the gears.

.Diesel engine bearings

. A bearing is a machined part which transmits the forces of loads from moving parts to stationary parts.

--. The two major types of bearings are rotary motion bearings and reciprocating motion bearings.

-- . Rotary motion bearings and bushings may be either a journal bearing or a thrust bearing or a combination of both.

) The journal bearings provide support normal to the axis of rotation.

) The thrust bearings provide support along the axis of rotation.

) Some bearings will provide support for both loads.

--. Bearing construction - Diesel engine bearings operate under less than favorable conditions such as fluctuating load, high lube oil temperatures, lube oil contamination, and viscosity changes. Therefore, bearings must be constructed with the following characteristics:

) Good embedability

) High fatigue strength

) Good conformability

) Good bond between layers

. Bushings - Normally used in diesel engines for rotating motion such as crankshafts and camshafts, or reciprocating motion such as piston pins and rocker arm bushings. Most bushings are made of a bronze or bronze with a babbitt lining.

--. Connecting rod and main bearings

) These are constructed in halves for ease of installation. The bearings used in modern diesels are precision type bearings and do not need to be fitted to the shaft. They are normally grooved for lubrication.

) The bearing material used in modern diesels are usually one of four types of material.

--) Bronze or steel back Satco - The back is either steel or bronze and the bearing face is Satco (99% lead and 1% tin).

-- ) Tri-metal bearing - Will have a steel back, intermediate layer of bronze, and the face will be made of the lead and tin based babbitt

-- ) Copper lead - If they have a back, it will normally be made of steel, tin, or indium plated to prevent corrosion.

-- ) Aluminum alloy - If these have a back, they will be made of steel with a bearing face that has a 6% tin content.

) Bearing installation - It is important that bearings be installed correctly (top and bottom). It is also important that bearings be kept clean and well lubricated prior to installation. Bearing caps must be properly torqued to ensure proper tightness.

) Bearing problems - Bearings that are properly cared for will last almost indefinitely. The biggest enemy of any engine bearing is dirt and poor quality lubrication. If a diesel engine has a good lube oil quality management program and is operated within specified engine parameters (temperatures and pressures) the bearings will last indefinitely.

) Crankshaft deflection readings - The deflection readings are an excellent method to determine engine to drive alignment and main bearing wear. Deflection readings should be taken as per the planned maintenance system, when a diesel inspection is conducted, when a problem is suspected, upon grounding or collision, and after a dry-docking period.