Crankshafts and Related Parts

The primary function of the crankshaft in an internal combustion engine is to:

Open and close the valves at the correct time Convert the reciprocating motion of the pistons into rotary motion Pump coolant through the block and head Control the air–fuel ratio in the intake system

Main journals on a crankshaft are the surfaces that:

Connect to the pistons Run in the main bearings and support the crankshaft in the block Support the flywheel only Drive the camshaft directly

Crankshaft rod journals are offset from the centreline in order to:

Reduce engine displacement Provide crank throw for piston stroke and connect to the connecting rods Support the timing belt sprocket Mount the vibration damper

Counterweights on a crankshaft are provided to:

Increase oil capacity Balance rotating and reciprocating masses and reduce bearing loads Increase combustion pressure Seal the rear main bearing

The ILM notes that crankshafts in most light and medium-duty engines are constructed from:

Plastics or composites Forged or cast steel/iron alloys designed for strength and fatigue resistance Aluminum for maximum lightness in all applications Glass fibre materials

Crankshaft fillets at the transitions between journals and webs are important because they:

Provide cosmetic appearance only Reduce stress concentration and help prevent fatigue cracks Increase surface roughness for oil retention Act as oil seals

The thrust bearing surfaces on a crankshaft are designed to:

Control up-and-down movement of the crankshaft Control end play (fore-and-aft movement) of the crankshaft in the block Support the camshaft drive Seal coolant passages

Crankshaft end play that is excessive can lead to:

Improved clutch life Clutch engagement problems, noise and possible damage to thrust surfaces Higher oil pressure Reduced gear noise

The rear main seal is located:

At the front of the engine behind the vibration damper At the back of the engine where the crankshaft exits the block to drive the flywheel or flexplate Around the camshaft Around each rod journal

A one-piece rear main seal design differs from a two-piece design because it:

Cannot be replaced Is installed around the crankshaft without removing the crankshaft from the engine block on many designs Is made of metal instead of elastomer Requires splitting the crankshaft

A vibration damper (harmonic balancer) mounted on the crankshaft is used to:

Increase alternator charging capacity Reduce torsional vibrations and protect the crankshaft from fatigue Control ignition timing electronically Change compression ratio

The keyway on the crankshaft nose is used to:

Circulate coolant Locate crankshaft-driven components such as timing sprockets or pulleys Inject fuel into the combustion chamber Vent crankcase gases

Crankshaft balancing in the ILM refers to:

Adjusting valve lash Distributing mass so that rotating forces do not cause excessive vibration Balancing the vehicle tires Balancing coolant flow

The crankshaft and flywheel together must be matched because:

They share paint colour codes They are often balanced as an assembly to reduce vibration They are both made of plastic They use the same bolts as the cylinder head

Crankshaft oil passages are drilled internally to:

Carry coolant to the pistons Direct pressurized oil from main journals to rod journals Store fuel for injectors Relieve compression pressure

An undersize crankshaft journal is one that:

Is larger than standard diameter Has been ground smaller than standard to clean up wear, requiring matching undersize bearings Uses standard bearings with extra clearance Cannot be used with any bearings

From a parts technician’s viewpoint, crankshaft-related parts may include:

Only flywheels Crankshafts, main and rod bearing sets, rear main seals, front seals, vibration dampers and flywheel bolts Only pistons and rings Only timing belts

The ILM notes that evidence of a twisted or bent crankshaft can include:

Perfectly uniform bearing wear Uneven bearing wear, vibration and difficulty aligning main bearings Improved fuel economy Lower emissions

A dual-mass flywheel used with some crankshafts is designed to:

Increase engine braking only Isolate drivetrain from torsional vibrations and improve shift quality Increase engine weight Eliminate the need for a clutch

The crankshaft in many heavy-duty diesels is supported by:

One main bearing at each end only Multiple large main bearings along its length to handle high combustion loads No bearings at all Roller bearings only

Crankshaft thrust surfaces are usually located at:

Any random main bearing A specific main bearing position designated by the manufacturer The rod journals The rear main seal housing only

When ordering a replacement crankshaft, the ILM stresses the importance of:

Matching only the number of cylinders Obtaining correct engine code, journal size, balance type and nose/flywheel configurations Guessing based on visual inspection only Using any crankshaft with the same firing order

Crankshaft runout is checked to determine whether:

The camshaft is bent The crankshaft is straight within specified limits The block deck is warped The cylinder head is cracked

Main and rod bearing clearances that are too tight can:

Improve lubrication Cause excessive heat, oil film breakdown and possible bearing seizure Have no effect on bearing life Reduce oil temperature

Flywheels are bolted to the crankshaft in order to:

Cool the engine oil Provide inertia for smoother rotation and a mounting surface for the clutch or torque converter Adjust compression ratio Control valve timing

Flexplates are used on engines equipped with:

Manual transmissions Automatic transmissions with torque converters No transmission at all Chain drives only

Crankshaft position sensors typically read:

Coolant temperature A toothed reluctor or machined pattern on the crankshaft or flywheel Fuel pressure directly Oil viscosity

Crankshaft damage from oil starvation often appears as:

Perfectly polished journals with no heat marks Blue discolouration, scoring and bearing material transfer Improved journal finish Reduced bearing wear

The ILM notes that rear main seal leaks are commonly misdiagnosed and may actually be caused by:

Tire imbalance Valve cover or intake manifold leaks running down the engine Incorrect firing order Clogged air filter

Crankshaft oil slingers or scrolls on older designs were used to:

Increase coolant flow Help control oil at the rear main area before modern lip seals Adjust timing Support the camshaft

When supplying main and rod bearing sets, parts technicians must match:

Only the number of bearings required Engine family, journal size (standard or undersize) and bearing material type recommended Any similar bearing that fits physically Only the thickness of the bearing shell

On some engines, crankshaft and bearing cap orientation is critical because:

Caps and crank can be installed in any direction They are machined as matched sets and must be reinstalled in original positions and directions Orientation only affects paint colour It determines tire pressure

The ILM emphasizes that replacement flywheel bolts are often:

Ordinary hardware store bolts High-strength fasteners that may be torque-to-yield and not suitable for reuse Not important to replace Made of plastic

Heavy-duty engines may use bolt-on counterweights on the crankshaft so that:

Balance can be adjusted or counterweights can be serviced separately Weight can be increased randomly Crankshaft can be removed more easily The flywheel can be eliminated