Lower End Theory and Service Engine Lower End The lower end of an engine is the cylinder block assembly Includes the block crankshaft bearings pistons connecting rods oil pump and camshaft on OHV designs ID: 331704
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Slide1
Chapter 11
Lower End Theory and ServiceSlide2
Engine Lower End
The lower end of an engine is the cylinder block assembly
Includes the block, crankshaft, bearings, pistons, connecting rods, oil pump, and camshaft on OHV designs
This assembly is called a short block
A short block plus the cylinder head(s) is called a long blockSlide3
Lower EndSlide4
Short Block Disassembly
Remove oil pan and water pump
Remove the harmonic balancer
On OHV engines remove the timing cover
Inspect the timing chain and remove
Remove the oil pick up and oil pump
Remove lifters and keep them in orderSlide5
Cylinder Block Disassembly
Check balance shaft clearances if necessary and remove
Rotate crankshaft so cylinder #1 is at BDC
Carefully remove all cylinder ring ridgesSlide6
Cylinder Block Disassembly
Check bearing cap positions and mark if necessarySlide7
Cylinder Block Disassembly (Cont.)
Position piston at BDC for removal
Remove connecting rod cap and cover rod bolts to prevent cylinder damage
Carefully push the piston and rod with wooden handle
Be sure connecting rod does not damage the cylinder wallSlide8Slide9
Cylinder Block Disassembly (Cont.)
Remove the main bearing caps in the specified order
Some engines use a main bearing girdle or bedplate that houses the bearings
Carefully remove crank and store vertically
Remove the rear main oil seal and bearing insertsSlide10
Cylinder Block Disassembly (Cont.)
Remove the block core plugs and oil plugs to ensure thorough cleaning
Oil gallery plugsSlide11
Cylinder Block
Houses areas where combustion takes place
Can be cast iron, aluminum or magnesium
Cast iron is very strong but heavySlide12
Cylinder Block (Cont.)
Most aluminum blocks use cylinder liners
Usually cannot be machinedSlide13
Oil and coolant passages within the block allow for the flow of oil and coolant
Cylinder Block (Cont.)Slide14
Block Reconditioning
Inspect the block for cracks and damage
Clean all threaded bores with a thread chaser
Bolt holes should be slightly chamferedSlide15
Block Reconditioning (Cont.)
Aluminum blocks with damaged threads may require a threaded insert – called a HelicoilSlide16
Block Reconditioning (Cont.)
Deck flatness is important for proper cylinder head and intake manifold fitSlide17
Block Reconditioning (Cont.)
Inspect cylinder walls
Wall scoring or scuffing
Most wear is at top of cylinder
Measure taper and out-of-roundnessSlide18
Cylinder Bore Finish
Surface finish must act as an oil reservoir
Rings can be damaged by a rough surface
Too smooth will not hold enough oil
Desired finish is a crisscross patternSlide19
Cylinder Bore Finish (Cont.)
Deglaze if cylinder condition is within specifications
Honing removes a small amount of metal from the cylinder walls
Boring is performed when the cylinder walls are worn excessively
Oversized pistons and rings are used after boringSlide20
Knowledge Check
What may result if the cylinder bore finish is too smooth?Slide21
Lifter Bores
Inspect bores for cracks and excessive wear
Can be honed with a wheel cylinder hone
If the lifter bores exceed allowable wear, the block should be replacedSlide22
Crankshaft Saddle Alignment
Misalignment will cause the crankshaft to bend as it rotates
May be repaired by line boring
Badly warped blocks are replaced
Checked along the crankshaft saddle bore
Roundness should be checked as wellSlide23
Crankshaft Saddle AlignmentSlide24
After cleaning, the block should have new core and oil plugs installed
Coat the plug or bore lightly with a non-hardening sealer
Installing Core PlugsSlide25
Camshafts
Have a cam lobe for each exhaust and intake valve
Lobe height is proportional to valve lift
May drive distributor and/or oil pump
May be iron, steel, or hollowSlide26
OHV Camshafts
Works with lifters, pushrods, and rocker arms to open the valvesSlide27
Camshaft in BlockSlide28
OHC Camshafts
May be single or dual overhead camshafts
Can open valves directly or through lifters, followers, or rocker armsSlide29
Camshafts (Cont.)
Driven at half of crankshaft speed
Cam gears are twice the size of crank gears
Each intake and exhaust valve opens and closes once per crankshaft rotation
Valve opening and closing based on the shape of the cam lobeSlide30
Camshaft Terminology
The shape of the cam lobe is called the cam profile
Duration is the time the valve is open
Overlap is the time both the exhaust and intake valves are open at the same timeSlide31
Lobe TerminologySlide32
Camshaft Drives
Belt Drive
Sprockets on the crankshaft and the camshaft are linked by a neoprene beltSlide33
Camshaft Drives
Chain Drive
Sprockets on the crankshaft and the camshaft are linked by a continuous chainSlide34
Camshaft Drives
Gear Drive
A gear on the crankshaft meshes directly with a gear on the camshaftSlide35
Camshaft Drives (Cont.)
Tensioners may be spring loaded and/or hydraulically operated
Maintains correct belt or chain tension
Have a drive side and a slack side
The tensioner is on the slack sideSlide36
Variable Valve Timing (VVT)
VVT used on OHC and OHV engine designs
VVT systems use special camshafts and phasersSlide37
Knowledge Check
What are the three types of camshaft drives?Slide38
Lifter Types - Hydraulic Lifter
Hydraulic Lifters
Uses oil to absorb the shock from the valve train movementSlide39
Lifter Types - Solid Lifter
Solid Lifters
Require a clearance between parts of the valve trainSlide40
Lifter Types - Roller Lifter
Roller Lifters
Uses a roller to minimize frictionSlide41
Camshaft Bearings
OHV engines are one piece bearings pressed into the camshaft bore
OHC can be supported by split bearingsSlide42
Balance Shafts
Balance or silence shafts are used to reduce engine vibration
Counterweights mirror the throws of the crankshaft
Rotate opposite crankshaft rotation
Inspected and serviced as part of engine reconditioningSlide43
Balance Shaft (Cont.)Slide44
Crankshafts
Made of iron or steel
Crankshaft main and rod journals are machined to very close tolerances
This allows an oil film between the journal and the bearingSlide45Slide46
Crankshaft Torsional Dampers
Crankshaft twists and bends under combustion forces causing harmonic vibrations
This vibration can damage the crankshaft, the engine, and/or accessories driven by the crankshaft
Two common types of torsional dampers usedSlide47
Harmonic Balancer
Also called a vibration dampener
Composed of an inner hub and outer inertia ring connected via a rubber sleeve
As the crank twists the hub applies force to the ring
The condition of the sleeve is criticalSlide48
Harmonic BalancerSlide49
Fluid Damper
Commonly installed by the aftermarket
Fluid filled dampers have a hub surrounded by the inertia ring
The ring is filled with a high viscosity fluid
The outer ring moves against the hub as it absorbs vibrations
This movement results in heatSlide50
Flywheel
Helps the engine run smoother
Applies a constantly moving force to the crankshaft
Flywheel inertia helps keep the crank moving from one firing event to the next
On automatic transmissions, the flex-plate and torque converter act as a flywheelSlide51
Check vibration damper and flywheel mounting surfaces for fretting or erosion
Look for indications of damage from previous engine failures
Check journals for signs of overheating
Check sealing surfaces for scoring or wear
Check for surface cracks
Crankshaft InspectionSlide52
Journal InspectionSlide53
Crankshaft Reconditioning
If severely damaged, the crank should be replaced
Slight journal taper, light grooves, burnt marks, or small nicks could allow reuse
Minor journal damage may be corrected by polishing with a very fine sand paperSlide54
Crankshaft Straightness
Checked by supporting the crank in V-blocks at the end main bearing journals
Position a dial indicator to measure at the center main bearing journal
Turn the crank one full rotationSlide55
Crankshaft Bearings
Called insert bearings
A split bearing with a flanged side is a thrust bearing
Many engines use bedplates instead of individual bearing caps
Tightening procedures must be followedSlide56Slide57
Bearing Materials
Aluminum alloy
The most commonly used design
Aluminum
Copper and lead alloys
Steel backings coated with babbitt
Layered combination of metalsSlide58
Bearing Spread and CrushSlide59
Locating lugs fit into slots in the bearing bore
Oil grooves provide an adequate oil supply
Oil holes allow control of oil flow to other parts of the engine
Bearing Locating DevicesSlide60
Knowledge Check
What is the purpose of the flanged main bearing?Slide61
Installing Main
Bearings and Crankshaft
If there is little or no wear on the journals, standard sized bearings can be used
If the journals are excessively worn, undersized bearings must be used
Undersized bearings are thicker since the crank journals are smallerSlide62Slide63
Installing Main
Bearings and Crankshaft (Cont.)
Plastigage is used to determine main and rod bearing clearances
Insert between the bearing and journal
Torque and then loosen the bearing capSlide64Slide65
Crankshaft End Play
Can be measured with feeler gauges or dial indicator
End play can be adjusted by replacing the main thrust bearing or washers
The crankshaft rear mail seal is usually installed during the final installation of the crankshaftSlide66Slide67
Connecting Rods
Transmits the pressure on the piston to the crankshaft
Made of steel, iron, aluminum, and titanium
The small end contains the piston pin
The big end attaches to the crankshaft and is in two pieces
May supply oil to cylinder wallSlide68Slide69
Pistons and Piston Rings
The piston forms the lower portion of the combustion chamber
Most are made of aluminum alloys
Piston heads can be flat, concave, convex, crowned, raised, and relieved for valvesSlide70
Pistons and Piston Rings
Below the head are the ring grooves and lands
Below the rings is the piston pin or wrist pinSlide71
Pistons and Piston Rings (Cont.)
The area below the pin is the piston skirt
Two types of skirts are used - the full skirt and the slipper skirt
Full skirts are used in truck and commercial enginesSlide72
Pistons and Piston Rings (Cont.)
The top of the piston has a direction mark
Mark or arrow points to the front of the engineSlide73
Check for damage and cracks, or scuffing on sides of the piston
Use a piston ring expander to remove rings
Clean carbon from piston top and ring grooves
Measure ring side clearance – between the ring and the top of the ring groove
Piston diameter should be measured
Piston InspectionSlide74
Piston Pins
Hollow steel tubes
Lubricated by oil fed through connecting rods
Stationary pins are pressed into the piston
Semi-floating pins are pressed into rod
Full-floating pins are retained by caps, plugs, snap rings, or clipsSlide75Slide76
Piston Pins (Cont.)
Inspect pin area on piston for wobble
Inspect pin for wear and pin bore in piston
Any movement up and down indicates either pin or piston needs replaced
Connecting rod may have a pin bushingSlide77
Seal the combustion chamber at the pistonRemove oil from the cylinder walls to prevent oil from entering the combustion chamber
Carry heat from the pistons to the cylinder walls to help cool the piston
Piston RingsSlide78
Compression RingsForm the seal between the piston and the cylinder wall
Most piston designs use two compression rings
Oil Control Rings
Control oil used to cool piston and lubricate cylinder walls
Piston Ring TypesSlide79
Piston RingsSlide80
Installing Rings
Check ring end gap
Apply a light coat of oil to the rings
Install the oil control ring first, staggering the ends of the three parts
Install the second then first compression rings
Ensure the correct side is facing up
Place ring gaps per specificationsSlide81Slide82Slide83
Knowledge Check
What is the correct order for installing piston rings?Slide84
Installing Pistons and Rods
Ensure caps and rods are a match
Insert bearings into rods and caps
Oil the cylinder walls
Coat the crankshaft journals with oil
After each piston in installed, rotate the crankshaft to check its movementSlide85
Checking Crankshaft RotationSlide86
Inspection of Camshaft
and Related Parts
Check each lobe for scoring, scuffing, fracturing, pitting, and signs of abnormal wear
Premature lobe wear is usually due to inadequate lubrication
Measure cam bearing journal diameter
Check for straightness with a dial indicatorSlide87
Timing Components
Measure timing gear backlash
Excessive backlash causes gear noise
Insufficient backlash causes gear bindingSlide88
Lifters
Inspect cam side for wear
Improper lubrication will cause excessive wear
Disassemble and clean lifters
Perform a leakdown test
Never use old lifters on a new cam or an old cam with new liftersSlide89
Checking Lifter WearSlide90
Installation – Camshaft Bearings
Cam-in block bearings may be easier to install if crankshaft is not installed
Bearings are press fit into block using a driver
Some cam journals have different diameters
Smallest at the rear of the block and each journal progressively largerSlide91
Camshaft Bearing InstallationSlide92
Installation - Camshaft
Thoroughly coat with assembly lube
Lubricate the lifters
Carefully install cam to avoid bearing damage
Install the thrust plate and cam gear
Once installed, turn the cam by handSlide93
Crank and Cam Timing
Timing must be set to specifications
Install the chain on the crank gear first
Never wind or pry a chain onto the gears
Check camshaft end play if requiredSlide94
Typical balance shaft timing mark arrangementSlide95
Balance Shafts
Inspect each bearing and journal
Check oil clearances with plastigage
Apply a light coat of oil to the bearings
Align the timing marks and set the shafts into positionSlide96
Oil Pumps
Positive Displacement Pumps
The amount of oil that leaves is the amount that entered
Output volume is proportional to pump speed
Internal engine passages restrict oil flow, causing oil pressure
Oil pressure affected by oil viscosity and temperatureSlide97
Knowledge Check
What may result from the balance shaft not being properly timed?Slide98
Rotor-type oil pump
Gear-type oil pump
Types of Oil Pumps