CH11 lower end theory and service STUDENT VERSION rev

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Chapter 11

Lower End Theory and Service

Cylinder Block Disassembly

• 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

• 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’d)

Cylinder Block Disassembly

(cont’d)

• Remove the block core plugs and oil plugs

to ensure thorough cleaning

Oil gallery plugs

Block Reconditioning

• Clean all threaded bores with a thread chaser

• Bolt holes should be slightly chamfered

• Aluminum blocks with damaged threads may require a threaded insert – called a Helicoil

• Inspect the block for cracks and damage

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

• 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

Lobe Terminology

Timing Drive Mechanisms

Camshaft Drives

• 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)

Lifter Types - Hydraulic Lifter

• Hydraulic Lifters

– Uses oil to

absorb the shock

from the valve

train movement.

Lifter Types - Solid Lifter

Lifter Types - Roller Lifter

• Roller Lifters

– Uses a roller to

minimize friction.

• Rotate opposite crankshaft rotation.

• Inspected and serviced as part of engine

reconditioning

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

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

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

– 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.

Bearing Failure and Inspection

Installing Main Bearings and Crankshaft

• 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

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 Ring Types

• 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 (cont’d)

• Compression 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.

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

Check lobe wear with a micrometer

Checking Lifter Wear

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

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

Typical

balance shaft timing mark arrangement

Types of Oil Pumps

• Rotor-type oil pump

• Gear-type oil pump

Types of Oil Pumps (cont’d)

• A pressure relief valve controls maximum

pressure.

• Inspect relief valve, gears or rotor, pump

housing, and gear to pump housing clearance.

• Ensure proper pickup screen placement.

• Use new gaskets and seals for pump and

pickup.