Lower End Theory and Service Chapter 11 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 This assembly is called a short block A short block plus the cylinder head(s) is called a long block

Lower End

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 order

Cylinder Block Disassembly Check balance shaft clearances if necessary and remove Rotate crankshaft so cylinder #1 is at BDC Carefully remove all cylinder ring ridges

Cylinder Block Disassembly Check bearing cap positions and mark if necessary

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 wall

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 inserts

Cylinder Block Disassembly (Cont.) Remove the block core plugs and oil plugs to ensure thorough cleaning Oil gallery plugs

Cylinder Block Houses areas where combustion takes place Can be cast iron, aluminum or magnesium Cast iron is very strong but heavy

Cylinder Block (Cont.) Most aluminum blocks use cylinder liners Usually cannot be machined

Cylinder Block (Cont.) Oil and coolant passages within the block allow for the flow of oil and coolant

Block Reconditioning Inspect the block for cracks and damage Clean all threaded bores with a thread chaser Bolt holes should be slightly chamfered

Block Reconditioning (Cont.) Aluminum blocks with damaged threads may require a threaded insert – called a Helicoil

Block Reconditioning (Cont.) Deck flatness is important for proper cylinder head and intake manifold fit

Block Reconditioning (Cont.) Inspect cylinder walls Wall scoring or scuffing Most wear is at top of cylinder Measure taper and out-of-roundness

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 pattern

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 boring

Knowledge Check What may result if the cylinder bore finish is too smooth? Oil may not be retained and the rings will not be lubricated as the piston moves up and down the cylinder.

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 replaced

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 well

Crankshaft Saddle Alignment

Installing Core Plugs After cleaning, the block should have new core and oil plugs installed Coat the plug or bore lightly with a non-hardening sealer

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 hollow

OHV Camshafts Works with lifters, pushrods, and rocker arms to open the valves

Camshaft in Block

OHC Camshafts May be single or dual overhead camshafts Can open valves directly or through lifters, followers, or rocker arms

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 lobe

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 time

Lobe Terminology

Camshaft Drives Belt Drive Sprockets on the crankshaft and the camshaft are linked by a neoprene belt

Camshaft Drives Chain Drive Sprockets on the crankshaft and the camshaft are linked by a continuous chain

Camshaft Drives Gear Drive A gear on the crankshaft meshes directly with a gear on the camshaft

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 side

Variable Valve Timing (VVT) VVT used on OHC and OHV engine designs VVT systems use special camshafts and phasers

Knowledge Check What are the three types of camshaft drives? Chain, belt, and gear.

Lifter Types - Hydraulic Lifter Hydraulic Lifters Uses oil to absorb the shock from the valve train movement

Lifter Types - Solid Lifter Solid Lifters Require a clearance between parts of the valve train

Lifter Types - Roller Lifter Roller Lifters Uses a roller to minimize friction

Camshaft Bearings OHV engines are one piece bearings pressed into the camshaft bore OHC can be supported by split bearings

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 reconditioning

Balance Shaft (Cont.)

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 bearing

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 used

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 critical

Harmonic Balancer

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 heat

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 flywheel

Crankshaft Inspection 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

Journal Inspection

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 paper

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 rotation

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 followed

Bearing Materials Aluminum alloy Aluminum Copper and lead alloys The most commonly used design Aluminum Copper and lead alloys Steel backings coated with babbitt Layered combination of metals

Bearing Spread and Crush

Bearing Locating Devices 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

Knowledge Check What is the purpose of the flanged main bearing? To control thrust or lateral movement of the crankshaft within the block.

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 smaller

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 cap

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 crankshaft

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 wall

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 valves

Pistons and Piston Rings Below the head are the ring grooves and lands Below the rings is the piston pin or wrist pin

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 engines

Pistons and Piston Rings (Cont.) The top of the piston has a direction mark Mark or arrow points to the front of the engine

Piston Inspection 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 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 clips

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 bushing

Piston Rings Seal the combustion chamber at the piston Remove 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 Ring Types Compression Rings Oil Control Rings Form 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 Rings

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 specifications

Knowledge Check What is the correct order for installing piston rings? Oil rings, second compression, top compression.

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 movement

Checking Crankshaft Rotation

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 indicator

Timing Components Measure timing gear backlash Excessive backlash causes gear noise Insufficient backlash causes gear binding

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 lifters

Checking Lifter Wear

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 larger

Camshaft Bearing Installation

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 hand

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 required

Typical balance shaft timing mark arrangement

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 position

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 temperature

Knowledge Check What may result from the balance shaft not being properly timed? Engine vibration.

Types of Oil Pumps Rotor-type oil pump Gear-type oil pump