MediumHeavy Duty Truck Engines Fuel Computerized Management Systems

Medium/Heavy Duty Truck Engines, Fuel & Computerized Management Systems, 3 E Chapter 7 Diesel Engine Power Train Assemblies Copyright © 2009 Delmar, Cengage Learning

Introduction • The internal works on an engine include a grouping of parts responsible for transmitting the gas pressures developed in the cylinders to a power take off mechanism • This mechanism is usually the engine’s flywheel Copyright © 2009 Delmar, Cengage Learning

Power Flow Components • • • Copyright © 2009 Delmar, Cengage Learning Pistons Piston Rings Wrist Pins Connecting Rods Crankshaft Friction Bearings

Power Flow Components • • • Copyright © 2009 Delmar, Cengage Learning Cylinder Pressure Piston Connecting Rod Crankshaft Power out

Piston Assemblies q The Piston ü A circular plug ü Seals the cylinder bore ü Reciprocates within the bore q The Piston Assembly Includes: ü Piston Rings ü Wrist Pin Copyright © 2009 Delmar, Cengage Learning Subject to the gas pressure conditions within the cylinder Imparts force on the compression stroke Receives force on the powerstroke Connects the piston to the connecting rod

General Piston Terminology A typical forged steel trunk piston used on many current diesel engines Copyright © 2009 Delmar, Cengage Learning

Piston Design “Mexican Hat” design common in Valvecrown Pockets emission DI engines! With a “Lowlow Clearance Volume” design, the piston rises in the bore to a height that requires q Piston Crown recesses to accommodate the valve head ü Direct exposure protrusion to combustion chamber ü Geometry controls gas dynamics ü Designed with low clearance volume ü Pistons absorbs up to 20% of rejected heat of cylinder gases ü Essential ability: Rapidly dissipate heat Copyright © 2009 Delmar, Cengage Learning

Piston Design Terminology Piston Style Trunk Aluminum Forged Steel Cam Ground Copyright © 2009 Delmar, Cengage Learning Articulating Composite Steel Separate Skirt Full Articulating Crosshead

Trunk Style Pistons § Aluminum Alloy ü Low weight ü Toughening treatments: The advantage of the aluminum’s low weight was offset by a lack of Commonly used in“toughness”. most commercial metallurgic dieseland engines until the 1990’swere Alloying surface treatments introduced as solutions ü Hypereutectic process Advantages: ü Anodizing • Lighter piston weight ü Plating • Less mass and inertia forces against the ü Heat treating connecting rods and crankshaft. ü Fiber reinforcing • Allows the use of lighter components § Ceramic (CFA) • Cooler crown temperatures aluminum’s high coefficient of heat Warning!! § Squeeze cast (SCFR) piston. With expansion, diesel pistons are “cam ground” Subjecting a diesel engine TM (with • Quieter operation. Less combustion Usually a Ni-Resist insert for ü Ring groove insert used engine tocam be slightly elliptical when cold. At the ground pistons) to high cylinder resistance to to high temperatures. This related noise compared articulating piston heats, before the piston material expands to ü Cam ground pressures the engine is at product has an identical coefficient of pistons a circular shape operating temperatures over-stress heat expansion to thatcan of aluminum § Silicone Copyright © 2009 Delmar, Cengage Learning the piston rings and ring lands!

Trunk Style Pistons § Forged Steel 2004 Cummins 2007 ISX 2010 ü First introduced in drag racing applications ü Introduced to diesel engine service in 2002 ü Currently used by many OEM’s to meet emission standards ü Design adoptedof bythe diesel engine. Forge OEM’s. Steel originated with Advantages Mahle Piston piston design specialist Mahle • Piston “slap” overcome with the Monotherm. TM design. TM The Monotherm ü The skirt is designed to aguide • Since the steel expands at lesser rate than aluminum, A MAHLE designed piston the piston over the thrust tolerances to the cylinder bore sides are much tighter. and is recessed across the pin • The alloyed strength of the construction allows less material to be Note: boss transverse used. Large resulting in a piston weight circumferential slot between the comparable to aluminum. andis ring belt • The wristpin pinboss bore phosphate treated, eliminating the need for § Designed for cylinder pressures bushings exceeding 3500 psi (250 bar) Copyright © 2009 Delmar, Cengage Learning

Advantages of Forged Steel Trunk Pistons • Increased cylinder combustion pressures ü Reduction of “Headland Volume” • Material strength allows the top ring to be placed closer to the crown leading edge • Engine longevity concerns ü More favorable thermal expansion factors • Less vulnerability of piston damage by high cylinder pressures during cold start-up • Phosphate coatings provide longer service life than aluminum counterparts • Lighter weight • Emissions Copyright © 2009 Delmar, Cengage Learning

Composite Steel Trunk Pistons • In the process of being introduced to the industry • Variation of forged steel trunk style piston • Mahle version will be know as Monocomp. TM Crown Manufactured from high temperature steel Trunk Steel skirt manufactured separately. Components joined together to create assembly Copyright © 2009 Delmar, Cengage Learning

Articulating Pistons • Adopted by most diesel engine OEM’s during the 1990’s • Usage recently dropped off in favor of forged steel and composite steel trunk type pistons Favored by Detroit Diesel for many years • Two styles ü Crosshead – semi floating wrist pin A Mack Truck three ring articulating piston used in ü Full articulating full floating wrist pin the “E-Tech”–engines. The crown has been raised slightly to illustrate the separate components Copyright © 2009 Delmar, Cengage Learning

Articulating Pistons • Advantages ü The crown is either forged steel or cast iron: § More suitable for high cylinder pressures § Sustains higher cylinder temperatures § Allows for reduced headland volume essential for reducing emissions and improving fuel economy § Greater longevity compared to aluminum trunk style ü The skirt may be made from a lighter material ü Reduced piston slap • Disadvantages ü Weight and tensional loading on the powertrain § Requires “beefed up” block and powertrain components Copyright © 2009 Delmar, Cengage Learning

Combustion Chamber Designs • Direct Injection (DI) Ø Piston crown shape determines gas dynamics • High Turbulence Design High turbulence design may disadvantage emissions by ü Injector positioned directly over piston crownfuel outside of “throwing” primary flame front causing ü Aggressive crown geometry = aggressive cylinder turbulence late ignition and unwanted afterburn! ü Larger injected fuel droplets require aggressive turbulence § Turbulence “rips” droplets into smaller droplets ü Modern designs & higher injection pressures reduced need for the “high turbulence” design ü Multi pulse fuel injection has seen a revisiting of the high turbulence design. Copyright © 2009 Delmar, Cengage Learning

Combustion Chamber Designs • Mexican Hat Piston Crown ü Most common design ü Central piston area recessed § “Toroidal recess” ü Aggressiveness of central cone designed to produce desired turbulence ü Injector positioned directly above center With this design, fuel droplets can be directed into ü Directs fuel towards crater where air the crater and will ignite swirl is greatest before touching the crown material. ü Deep bowl designs produce greater turbulence This prevents fuel burnout ü“Quiescent” designs use low turbulence & higher injection scorching of the piston pressures directly below the injector, Copyright © 2009 Delmar, Cengage Learning lengthening service life

Combustion Chamber Designs Other Piston Crown Designs • Mann ü Also known as “M” Type ü Designed and named after German originating company ü Features a spherical recess directly under the injector ü Recess not necessarily in center of crown ü Produces high turbulence ü More vulnerable to localized burnout in bowl Copyright © 2009 Delmar, Cengage Learning • Dished ü Used in: ü Some small bore engines ü Some IDI engines ü Slightly concave (almost flat) ü Produces low turbulence Also known as a bowl

Piston Heat Management ü Combustion temperatures can have transient spikes to 2000 o C or 3630 o F ü Piston material – role as a “heat siphon” § Aluminum melts @ 660 o C or 1220 o F Heat flow through aluminum is approximately o or 2800 o F § Cast Iron melts @three 1540 times. C greater than cast iron! ü Some heat transferred to the cylinder walls through the piston rings ü Cooling is often assisted with an oil spray to piston’s underside Copyright © 2009 Delmar, Cengage Learning

Piston Cooling • Cooling method determination: Caution! Oil is delivered through the connecting rod to • Size of piston A misaligned spray nozzle can cause premature galleries under the piston crown. • Peak cylinder pressure engine failure ! Oil is distributed by piston motion & returned Some newer engines rely entirely on oil spray to the crankcase • Aspiration to cool and lubricate the piston assembly • Some heat is transferred Oil is delivered through the connecting rod & wrist pins. Circulated through a series of through piston assembly grooves machined into the underside of the piston crown & returned to the crankcase • Methods used to cool piston A stationary jet mounted to the engine block directs a spray of directly to the underside of heads: ü Shaker ü Circulation ü Spray Copyright © 2009 Delmar, Cengage Learning the piston. In addition to cooling, the oil may also lubricate the wrist pin. Most current in use.

Piston Fit Problems • Excessive Clearance ü Piston knocking ü More noticeable: üWhen cold üWith aluminum trunk pistons • Inadequate Clearance üPiston scoring üPiston scuffing (localized welding) ØLubricating oil film scraped from cylinder walls Copyright © 2009 Delmar, Cengage Learning

Piston Assembly Overview Compression Ring Location Includes “Scraper Ring” Ring Lands Compression ring finish & design is critical to establishing cylinder seal Oil Control Ring Location Oil Control Rings Note “channel “ design The number of rings used is determined by the OEM. Factors include bore size, engine speed & configuration Copyright © 2009 Delmar, Cengage Learning Ring drain slots work in conjunction Oil drain with slots the piston’s drain holes

Piston Thrust and Antithrust Thrust face Anti Thrust Face

Piston Rings • Function: ü Seal piston in bore Ø Compression Ø Combustion gases ü Lubrication Ø Apply film of lubricant to cylinder wall Ø Regulate amount of film on the cylinder wall ü Cooling Ø Provide a path to transfer heat from the piston to the cylinder wall Copyright © 2009 Delmar, Cengage Learning

Roles of Piston Rings Categories • Seals engine cylinder Compression • Dissipates piston heat Compression Copyright © 2009 Delmar, Cengage Learning

Roles of Piston Rings Categories Compression Scraper • Seals engine cylinder • Dissipates piston heat • Seals engine cylinder • Manages oil film on cylinder wall Copyright © 2009 Delmar, Cengage Learning

Roles of Piston Rings Categories Compression Scraper • Seals engine cylinder • Dissipates piston heat • Seals engine cylinder • Manages oil film on cylinder wall Oil Control • Lubricates cylinder walls Oil Control • Dissipates piston heat Copyright © 2009 Delmar, Cengage Learning

Compression Ring Geometry • Primary Function ü Sealing cylinder gases • Face Types ü Keystone/Trapezoidal ü Barrel faced ü Rectangular ü Inside Bevel ü Taper Faced • Joint Types ü Straight ü Angle ü Step Copyright © 2009 Delmar, Cengage Learning • Major sealing force -- cylinder gases • Pressure forces ring downward to land • Pressure gets behind ring • Ring is forced outwards by pressure • The higher the cylinder pressure, the tighter the seal! • • • The angled outer face Internal Outer surface peripheral “barreled” recess with allows radius cylinder Wedge shaped Preferred when ring isachieves made ofahigher cast iron sealing pressures. • due Defined bybehind the “L” shaped step at the gas Designed to to increase twisting service the life ring. Commonly used as top ring toget the even “loading” achieved. joint. • abutting by the complimentary angles athigh the This No sharp twisting “bite” effect intoresults the cylinder in unusually wall Gas pressure easily gets behind to assist • Defined Lower sealing pressures. • with Affords the leastrings potential for is cylinder gas joint. sealing Many keystone pressures are style barrel faced. sealing • The Greater longevity. • abutting disadvantage of this the greater • leakage athe fairly efficient seal. • Provides Used asatof second or third compression ring in potential gasjoint “blow-by. where a used keystone style is • some This isapplications the most commonly design in the top position. • used Gas that blows by all the rings enters the crankcase • Crankcase pressures could be an indication of overall engine health.

Ring Construction • Modern compression rings are coated Ø To reduce friction Ø To facilitate “run in” • Combination Compression & Scraper Rings Some “break-in” The adding & circumferential expander (spring) forces theremoval Ø If used, A located in intermediate area of ring belt coatings will end up oil is also the removal oil control ring into the cylinderofwalls Ø Designed to assist with cylinder sealing & oilthefilm control in the crankcase…remember of heat from cylinder walls • Oil Control Ring this when examining oil sample reports! Ø Manages lubricant film § Excessive oil will end up in combustion chamber § Inadequate will result in scoring & scuffing Ø Conformable § Ring flexes to accommodate moderate liner distortions Copyright © 2009 Delmar, Cengage Learning

Ring Construction • Piston & Cylinder Wall Lubrication ü Oil Control Rings ü Precisely manage cylinder oil film ü Piston Downstroke ü Oil is forced into the lower part ring groove ü Piston Upstroke ü Oil accumulated on the downstroke transferred to the upper side of ring land ü Oil is applied to the cylinder Copyright © 2009 Delmar, Cengage Learning

Compression Ring Construction • Modern compression rings are coated Ø To reduce friction Ø To facilitate “run in” • Combination Compression & Scraper Rings Ø If used, located in intermediate area of ring belt Ø Designed to assist with cylinder sealing & oil film control • Oil Control Ring Ø Manages lubricant film § Excessive oil will end up in combustion chamber § Inadequate will result in scoring & scuffing Ø Conformable § Ring flexes to accommodate moderate liner distortions Copyright © 2009 Delmar, Cengage Learning

Trying to. Rings stretch a ring by hand may: Installing Piston • Bend or break the ring • Crack the plating or cladding material • The correct tool is a wise investment • Never “over stretch” a ring Caution! ü Always use the correct tool ü Never install a cracked or chipped ring ü Most rings have an “up side” Ring Expander ØKnow how to determine the correct orientation! ü Always check ring “end gap” ü Always observe OEM instructions Copyright © 2009 Delmar, Cengage Learning

• Ring gap “stagger is” theoretically determined by dividing 360 o by the number of rings. • Ring gaps should not be placed directly over piston thrust faces • Always reference OEM literature Assembling Pistons & Rings • Ring Stagger ü Always observe OEM protocol ü Check ring side clearance A typical Mack ring stagger recommendation International’s recommendation for ring stagger & pressure balance Copyright © 2009 Delmar, Cengage Learning

Piston or Wrist Pins Maximum engine speed & expected cylinder pressure Piston Pins determines whether the pin will Function: be solid or bored through! • Primary – connect the piston to the connecting rod • With an articulating piston, the pin also connects the piston skirt to the piston crown • Power is transferred from the piston crown through the pin to the connecting rod Copyright © 2009 Delmar, Cengage Learning

Piston or Wrist Pins Piston Pin The bearing surfaces of the piston pin are lubricated in one of two ways: • Full floating piston pins are fitted to both the connecting rod & the piston boss with minimal clearance • Some newer piston bosses are bushingless! Copyright © 2009 Delmar, Cengage Learning

Piston or Wrist Pins Piston Pin The bearing surfaces of the piston pin are lubricated in one of two ways: 1. Directly through the connecting rod Copyright © 2009 Delmar, Cengage Learning

Piston or Wrist Pins Piston Pin The bearing surfaces of the piston pin are lubricated in one of two ways: 1. Directly through the connecting rod 2. By the piston cooling jet spray Copyright © 2009 Delmar, Cengage Learning

Piston or Wrist Pins All full floating piston pins need a method to secure them Piston Pin Retention 1. Snap rings 2. Plugs All plug style retainers Used by most must. OEM’s be checked for seal • Always observe integrity after installation. the installation instructions! • Snap rings Failure to doare so subject may result to inertia in excessive oil being • Failuretotothe added follow cylinder directions walls may result in engine failure Copyright © 2009 Delmar, Cengage Learning

Reusing Piston Assemblies • Reuse of pistons: ü Not a common practice with aluminum trunk style pistons ü More common with forged steel crown pistons ü Always observe OEM recommended practices ü Routine replacement may not be justified ü If performing engine work under warranty, determine if piston replacement is covered beforehand Copyright © 2009 Delmar, Cengage Learning

Reusing Piston Assemblies 1. Clean all crystallized carbon out of the ring grooves ü Use a correctly sized ring groove cleaner 2. Visually assess the condition of the ring groove 3. Measure the cleaned ring groove with a new ring installed square in the groove A broken compression ring the can bepiston, ground check 4. Before installing the new rings on square and used successfully the ring gap by installing the ring squarely into the cylinder and measuring with a thickness gauge 5. Always follow OEM specifications! 6. Always measure all new rings before installation! Copyright © 2009 Delmar, Cengage Learning

Connecting Rods • Transmits the force from the piston to the • After rodengines is fractured Most truck & bus diesel two piece Somemachining, OEMs usethe “cracked” oruse fractured crankshaft • rods Thetechnology rough surfaces provide a perfect final fit rod alignment thepiece, needsevered to checkand rod • These are eliminating forged in one • Ends have bearing surfaces side play after “bolted” machined reassembly Ø This allows the linear force to be converted to rotary action by the crank throw rotating around the crank’s centerline Copyright © 2009 Delmar, Cengage Learning

Compressional Loading • Connecting rod is “squeezed”: compressionally loaded: ü On the power stroke ü On the compression stroke • Very seldom is compressional loading a major contributing factor to rod failure • Increased compressional loading due to hydraulic lock may result in connecting rod failure For example: coolant leakage into the cylinder Copyright © 2009 Delmar, Cengage Learning

Tensional Loading • A connecting rod “stretches” • At TDC or BDC -- piston stops before changing direction • The greater the mass of the piston, the greater the inertial forces • The greater the inertia forces, the greater the tensional loading • Tensional loading increases with engine speed • Many OEMs offset the mating surfaces of the connecting rod’s “big end” to ensure the rod cap fasteners do not sustaining the full tensile loading of the rod Copyright © 2009 Delmar, Cengage Learning

Connecting Rod Reconditioning • Preparation Ø Remove piston pin bushing Ø Install & retorque rod cap • Measurement Ø Measure both bores Ø Check for straightness Ø Check for twisting Concentricity is critical! • Magnaflux for cracks • Install new bushings Always ensure that the new bushing’s • Check & clean oil passage oil hole is properly aligned with the Copyright © 2009 Delmar, Cengage Learning connecting rod’s passage!

Connecting Rod Reconditioning Failure to align the rod cap will result • Best Practices in crankshaft scoring in the areas of theisn’t web cheeks & engine through seizing. üEnsure the connecting rod “bruised” “Cracked rod” technology has reduced the dropping, hammering orneed clamping a vicerod caps, to align thein connecting although it is a good practice to check üBefore reconditioning connecting rods, check with clearance after assembly. A clacking noise Marks focal shouldcan be become heard asstress the rod is shifted across the specific manufacturer’s recommendations points & lead to separation failure! the crank throw. üA connecting rod set is “weight sensitive” üMany OEMs recommend the rod cap fasteners are Replacing or changing the weight rods of is not The reconditioning of connecting replaced with each reassembly a connecting rod on may result diesel in an widely practiced today’s unbalanced engine…check your specs! engines üWhen assembling the rod on the crankshaft check side clearance! Copyright © 2009 Delmar, Cengage Learning

Engine Crankshafts • Crankshaft ØA shaft with a series of throws • Typical throw locations (end view): In-line V-8 configuration 4 configuration 6 8 Copyright © 2009 Delmar, Cengage Learning “V” Configured Engines Some OEMs use unique numbering sequences: • DDC identified their V engine cylinders by bank & sequentially… 1 L -1 R, 2 L-2 R, etc.

Crankshaft Terminology Copyright © 2009 Delmar, Cengage Learning

Crankshafts & Bearings • Crankshaft ØPiston assemblies are connected via connecting rods ØConverts linear piston action to rotary motion ØSupported by friction bearings ØPressure lubrication is required to enable hydrodynamic suspension of the shaft within the bearing bores Copyright © 2009 Delmar, Cengage Learning

Hydrodynamic Suspension S ü Rotating shaft S S ü Pressurized lubricant S S ü Lubricant “picked S up” by shaft rotation S Crankshaft ü Wedge created • • Dynamic balance isismaintained Dynamic balance maintainedthroughthe theuse useof of ü Shaft suspended S crankshaft counterweights S • • The “weights” oppose the unbalancing forces ü Metal-to-metal The “weights” oppose the unbalancing forces S created by the pistons S surface contact • Unbalance forces tend to diminish as the number S of engine cylinders increase prevented Journal • Geometrically paired or companion throws contribute a counterbalancing effect Copyright © 2009 Delmar, Cengage Learning

Crankshaft Operational Forces • Bending • Torsional (twisting) ØOccurs between main ØOccurs between journals crank throws ØCreated by: üCompression üCombustion pressures These oscillations take place at high frequencies üSlowing of the crank journal on compression üAcceleration of the crank journal on combustion • Crankshaft design, materials & hardening methods must take these forces into account! Copyright © 2009 Delmar, Cengage Learning

Crankshaft Operational Forces • Torsional Stresses: üPeak at crank journal oil holes – flywheel end üAmplified at lower operational speeds & high cylinder pressures Traditionally, this would have been referred to as “lugging” the engine Make sure • Today’s diesel engines are designed tothe operate: drivetrain components üAt 30% lower speed match the output of the engine üWith 30% more torque These engines produce higher torsional oscillations that are projected through the drivetrain. Copyright © 2009 Delmar, Cengage Learning

Crankshaft Construction • Materials: ü Steel forgings ü Special cast iron alloys ü All materials are tempered (heat treated) • Designed to produce a tough flexible core • Most OEM crankshaft manufacturing processes are proprietary A technician’s understanding of hardening procedures is an essential consideration when addressing the reconditionability of a crankshaft! Copyright © 2009 Delmar, Cengage Learning

Crankshaft Hardening Methods • Three methods used: 1. Flame hardening (plain carbon & middle alloy steels) ü ü ü Direct application of heat Quenched with oil or water Produces surface hardening dependent on the carbon and alloys 2. Nitriding (alloy steels) ü ü Higher temperatures than flame hardening Hardens to a greater depth (0. 0225” or 0. 65 mm) 3. Induction hardening ü ü ü Heated by AC current through applicator coil Quenched with air blast or liquid Hardens to depths up to 0. 085” or 1. 75 mm Copyright © 2009 Delmar, Cengage Learning

Crankshaft Removal 1. Invert engine 2. Remove bearing caps 3. Remove any other obstructions 4. Use crankshaft yoke ü ü Cover yoke with rubber hose to protect the throws Select two adjacent “paired” throws 5. Lift crankshaft from block Copyright © 2009 Delmar, Cengage Learning • In a effort to reduce engine weight, OEMs use lighter alloys in the cylinder block. • To reduce block “twisting” bolster plates & buttress screws may be installed. • These must be removed to facilitate the removal of the bearing caps!

Crankshaft Failures • Causes: Ø Manufacturing defects Ø Bending failures Ø Torsional failures Bending start bearings Ø Spun failures or seized at the main journal Ø Etched bearings fillet & extend through the throw journal at 90 o toresult the crankshaft • Torsional fractures in Fan axis a circumferential severing Assemblies through the fillet. • In an inline 6 cylinder engine, #5 & #6 journals tend to be more vulnerable Copyright © 2009 Delmar, Cengage Learning • § • • Compressors • Lubrication related failures Today’s R&D very as thorough Misaligned Vibration A chemical damper action bearing orbores a result ü Misaligned oilorhole Main flywheel of contaminated bearing assembly: failure engine Only small percentage are a ü Improper clearance irregular lubricant ü Loose wear result of manufacturing and ü Restricted passages Idlers Main High ü Damaged acidity caps broken levels or can loose design problems ü bearing Contaminated oil Wrong corrode ü Defective all engine sizes metals Quickly remedied by OEMs • but Poor maintenance practices resulting Flywheel Unbalanced usually housing first engine noticed drive on ofin Fuel or coolant destroys the lubricity • Excessive clearance results in lubricant sludge plugged passages engine oil!main misaligned components engine bearings throwoff, starving journals furthest • This lead to etched bearings fromcould the supply Crankshaft Engine May beoverspeed as anot result properly of poor • Insufficient clearance caused by: PTOs supported Unbalanced maintenance when cylinder practices out of loading • Overtorquing Pulleys block Defective Appears asengine uneven mounts erosion • Undersized bearings installed a standard specification pockwhere marks or channels was required • Line bore irregularities

Crankshaft Inspection • Always check OEM recommendations Recommended by most OEMs at every out of • Usually includes: ü Measurement ü Visual inspection including Magnafluxing chassis overhaul • Magnaflux process assists with identification of faults Ø The crankshaft is magnetized and coated with iron filings Ø Magnetic lines of force will “bend” into cracks causing the filings to collect Ø Minute flaws can be detected with ultra-violet or black light • Always ensure a magnafluxed crankshaft has been demagnetized before reuse! Copyright © 2009 Delmar, Cengage Learning

Crankshaft Inspection • Visual ü Cracks (Magnaflux) • Most small cracks observed when Magnafluxing are harmless • Beware of fillet cracks & cracks extending into oil holes • Circumferential fillet cracks • Minor scratches & marks may be by polishing • 45 o cracks extending into fillet arearemoved or journal oil holesthe journals • Plug all oil passages ü Wear & roughness • Use a crank grinding lathe & rotate in the direction of engine rotation • Crankshaft thrust surfaces • Wet polish with a low abrasive • Front & rear main seal contact areas emery cloth Always exercise Most highway diesel engine crankshafts care when required working with special attention during the life of the engine rotating machinery! Copyright © 2009 Delmar, Cengage Learning no

Crankshaft Inspection • Measurement Micrometer Out of round ü Use precision measuring instruments Taper ü Measure at 90 o intervals ü Measure at 3 linear points • Typical maximums • Place the ends of the crankshaft in a set of “V” blocks • Using a dial indicator, rotate the crankshaft checking for deflection Ø Out of round: 0. 025 – 0. 050 mm (0. 001” – 0. 002”) Ø Taper: 0. 0375 mm (0. 0015”) • Check all crankshafts for bending – refer to OEM spec’s Copyright © 2009 Delmar, Cengage Learning

Reconditioning Crankshafts Note: Ø Most OEMs do not approve of reconditioning Although these processes exist, the industry crankshafts! consensus isprocess that they are bad practice & Ø A reconditioning must not compromise the • This process will require the representhardening! poor long-term economics! original surface installation of oversized • Reconditioning Processes: bearings • These may not be available through the OEM ü Grinding to undersize dimensions ü Metallizing & regrinding to specification ü Chroming surface to return to original size ü Submerged arc welding, regrinding to specification Copyright © 2009 Delmar, Cengage Learning

Rod & Main Bearings Construction & Design § Wall thickness § Concentric § Eccentric Materials Wall thickness is greater Wall thickness is uniform §at Steel base the crown compared to parting faces §the. Copper § Lead § Tin § Aluminum Copyright © 2009 Delmar, Cengage Learning All friction bearings are designed to have a degree of embedability The outer face must be soft enough to permit small abrasive particles to penetrate to a depth where they will cause a minimum of scoring

Bearing Clearance Green Coded Plastigage • 0. 001 – 0. 003 inch • 0. 025 – 0. 76 mm • Clearance critical to hydrodynamic suspension Note 3: 4: 2: 1: Red Coded Plastigage • Never assume a new engine has “standard” sized Clamp thewidth Plastigage between Compare Reference Never attempt the bearing to ofmeasure Plastigage the bearing and the journal bearings • 0. 002 – 0. 006 inch against clearance bearing the clearance specifications dimensional while before the gauge • 0. 051 -0. 152 mm provided starting engine istorque on in thethe chassis. Plastigage Always screws to the • Clearance is precisely measured packaging. specified Select thetorque! Crankshaft correct flexibility Plastigage will render to Blue Coded Plastigage Compare provide the results accurate toinvalid engine spec’s • Measurement is done with Do not rotate themeasurement crank with the Plastigage in place! • 0. 004 – 0. 009 inch Remove Place Invert a&piece the levelresidual across the engine the Plastigage center before “Plastigage” from of starting thethe bearing journal • 0. 102 -0. 229 mm Remove bearing cap Plastigage is manufactured in four Plastigage is a. Yellow malleable plastic thread Coded Plastigage sizes, each color coded for the range that easily deforms & conforms to of clearance it • is 0. 009 capable ofavailable inch whatever clearance space– is 0. 020 measuring when compressed • 0. 230 – 0. 510 mm Copyright © 2009 Delmar, Cengage Learning

Crankshaft End Play • One of the main bearings is usually flanged to define crankshaft end play • These surfaces are known as “thrust bearings” • Available in several sizes to accommodate wear • Some OEMs limit crankshaft end play through the use of split rings known as “thrust washers” Ø Usual end play (0. 2 – 0. 3 mm or 0. 008 -0. 012”) • Use a dial indicator to measure this dimension If thrust washers are used, place thicker washers to offset the effects of the clutch! Copyright © 2009 Delmar, Cengage Learning

Bearing Retention The tangs correspond to a matching groove in the bearing bore • Primarily retained by “crush” • Equipped with “tangs”, to minimize lateral travel The bearing OD of pressure radial the halves bearing are actsshell also against slightly theelliptical exceeds bearing halves the to allow diameter and theprovides bearing of the bore good to beinheat held which transfer. in place it is during installed. installation. This creates This radial is known pressure. as “spread”. Copyright © 2009 Delmar, Cengage Learning

Bearing Removal & Installation Always: ü Consult proper, current, service literature Do not use solvents or than any other Be careful, Use of anything whenother removing the ü Observe published procedures cleaning which may old bearings. engine oilchemicals may result in a failure • Bearing “Roll ins” leave residual film on the new Dothe of notacrankshaft mark or damage to create bearings! the crankshaft!support necessary hydrodynamic ü Performed while engine is in the chassis Today, this procedure is practiced more often than ü Handle the new bearings as little as possible necessary. ü not Ensure the backing is cleanaand It is uncommon to remove setdry of bearings in near perfect condition! ü Apply a thin film of engine oil to the bearing face ü Prime the lubrication circuit before cranking the engine Copyright © 2009 Delmar, Cengage Learning

Vibration Dampers General: ü Mounted on the free end of crankshaft (opposite flywheel end) ü Sometimes referred to as the harmonic balancer Purpose: ü Reduce the amplitude of vibration ü Assists the flywheel’s mass establishing rotary inertia ü Reduces torsional vibration Types: ü Solid rubber drive ü Viscous drive Copyright © 2009 Delmar, Cengage Learning

Viscous Style Construction Replacement: Driven Drive Medium Member • Member Most OEMs recommend the replacement of the • • Inertia Fluid Hollow (Silicone ring housing. Gel) • • Suspended Gel’s Boltedshearing toharmonic crankshaft by fluid action balancer at each major overhaul • atdamping Component life often exceeds projected • Rotates creates average crankshaft effect expectations speed • Seldom replaced due to expense considerations Ø Some risk involved Ø May result in failed crankshaft Replace if there is any sign of damper housing damage or fluid leakage! Copyright © 2009 Delmar, Cengage Learning

Solid Rubber Vibration Dampers • Less often used today ü Less effective at dampening torsionals on high torque, lower speed engines ü Construction: ü Drive hub bolted to crankshaft ü An outer inertia ring (contains most of the mass) ü A rubber ring, bonded to the hub and the outer ring Internal The elasticity friction of generates the heat rubbereventually which enables the hardens the unit to function rubber renderingasitaless effective dampening and vulnerable unitto shear failure Copyright © 2009 Delmar, Cengage Learning

Vibration Damper Inspection • Visual inspection ü Dents ü Warpage ü Run out (measured with a dial gauge) ü Fluid leakage (viscous style) • Physical Engine operating temperature 90 o C (180 o F) ü Remove from engine and shake the unit ü Heat unit – recheck for leakage ü Run unit in a lathe at engine speed – check for balance Copyright © 2009 Delmar, Cengage Learning

Flywheels • General ü Mounted at the rear of the engine • Function: ü Store kinetic energy in the form of Flywheel mass depends on: ü 2 cycle ü 4 Energy cycle of motion üEngine operating range The power take off üThe number of crank degrees device strokes to which the between power or torque inertia clutch converter is bolted Ø Smooth out the power pulses Ø Establish an even crankshaft rotation speed ü Provide a mounting for engine output ü Provide a means to rotate the engine via a cranking motor Copyright © 2009 Delmar, Cengage Learning

Types of Flywheels • Categorized by A typical service illustration of a 15 ½” flat faced flywheel the used SAE: on a Caterpillar engine ü Standardization allows for: • Different OEM Clutches • Different OEM Transmissions ü SAE #4 = 15 ½” clutch assembly ü Usually “flat face” design ü SAE #5 = 14” clutch assembly ü Usually “pot” design ü Construction: ü Cast iron ü Steel Copyright © 2009 Delmar, Cengage Learning • Most flywheel stresses peak at the juncture of the rim and hub an area subject to torsional & centrifugal loads • Flywheel stress failures are rare!

Flywheel Ring Gears • • Sometimes striking the cut section with a chisel is General: necessary to fully expand the Heating a Ring Gear ring gear for removal – Shrink fitted to the periphery of the flywheel • Only. Care practical method a must be takenistowith ensure rose the budflywheel oxyacetylene tip – Transmits cranking torque to the engine from the starter is not damaged • Usewith a temperature the torch! indicating Replacement Procedures: crayon to ensure the ring gear – Remove the flywheel from engine does not become overheated • The ring gear will almost – Partially cut the ring gear with an oxy-acetylene torch Ensure that the ring gear is the immediately contract to the correct one! • From the outside on a single tooth flywheel the teeth tongs are chamfered • Use If blacksmith to handleon • Ring gear will expand, allowing its removal onering side, they face the hot gear! – Place flywheel on a flat surface cranking motor pinion after • Check ring gear mounting surface installation • Heat the new ring gear & shrink fit it to flywheel Check OEM heat value. Typically, this specification would be around 200 o C although it may be as high as 315 o C Copyright © 2009 Delmar, Cengage Learning

Reconditioning Flywheels • Commonly removed for: ü Clutch damage ü Leaking rear main engine seals • Always inspect the flywheel for: ü ü ü When resurfacing a pot type flywheel, the pot face must have as much material removed as the flywheel face! Failure to do so will render the clutch inoperable! Face warpage Heat checks Scoring Intermediate drive lug alignment & integrity (pot type) Axial and radial run out • Flywheels may be machined – check OEM tolerances Copyright © 2009 Delmar, Cengage Learning

Summary • The engine power train comprises of those components that deliver the power developed in the cylinders to the power take off mechanism • Aluminum trunk type pistons were widely used until the late 1980’s Ø Due to their light weight & ability to transfer heat quickly Ø The top ring was supported with a Ni-Resist insert Ø These style of pistons were “cam ground” Ø Still in use today but mostly light duty diesel engines • Two piece articulating pistons replaced the aluminum trunks style Ø Favored by most OEMs until recently Copyright © 2009 Delmar, Cengage Learning

Summary • Articulating pistons comprised of: Ø A forged steel crown Ø An aluminum alloy skirt Ø Coupled together via the wrist pin • Current diesel engine OEMs favor a forged or composite steel trunk piston for their high output engines • The Mexican Hat style of crown is the most common design in today’s low emission, direct injected engines Copyright © 2009 Delmar, Cengage Learning

Summary • Engine oil is used to cool the pistons Ø Shaker design Ø Pressure circulation Ø Spray jet method • Piston rings seal the piston when cylinder pressure acts on the exposed sectional area of the ring Ø The efficiency of piston ring seal increases proportionally with cylinder pressure • Gases that pass by the rings are known as “blowby gases” Copyright © 2009 Delmar, Cengage Learning

Summary • The keystone ring is the most commonly used for the top compression ring • Oil control rings are designed to apply a film of lubricant on the piston upstroke & scrape the cylinder wall on the downstroke • Full floating wrist pins have bearing surfaces with both the piston boss and connecting rod eye • Crosshead pistons articulate but the semi-floating wrist pin bolts directly to the connecting rod’s small end Copyright © 2009 Delmar, Cengage Learning

Summary • Full floating wrist pins are retained in the piston bosses by snap rings. • Detroit Diesel 2 stroke engines retain wrist pins via press fit caps • Connecting rods are subject to compressional and tensional loads Ø Connecting rods will normally survive the life of engine but need to be thoroughly checked at each overhaul • Crankshafts are designed to withstand considerable bending & torsional stress Copyright © 2009 Delmar, Cengage Learning

Summary • Most medium & large bore diesel engines use induction hardened crankshafts • Engine OEMs do not approve of reconditioning failed crankshafts Ø However, the process is widespread despite the risk of subsequent failure! • Friction bearings used in crank throw & main journals are retained by “crush” • Vibration dampers consist of: Ø A drive member Ø Drive medium Ø Inertia ring Copyright © 2009 Delmar, Cengage Learning

Summary • The viscous style of damper is most commonly used on today’s truck & bus diesel engines • The shearing action of the silicone gel contained in the viscous damper effects the dampening of the engine • The flywheel stores kinetic energy in the form of inertia to help smooth power pulses delivered to the powertrain • Flywheels are categorized by size and shape Copyright © 2009 Delmar, Cengage Learning