Engines - Crankshaft Assembly and Pistons Flashcards
This engine component converts the downwards linear motion of the piston to usable rotary motion, while also tying all the pistons together to create one large timer rotary force.
the crankshaft
This engine component drives the camshaft.
the crankshaft
This engine component provides a mounting surface for the flywheel and harmonic balancer.
the crankshaft
This engine component if made from forged alloy steel, which is either flame or induction hardened.
the crankshaft
What are the four main parts of an engine crankshaft?
- main bearing journals
- connecting rod journals (or throws)
- webs
- counterweights
This part of a crankshaft supports the crank in the engine.
the main bearing journals
This part of a crankshaft is off-centre to harness the piston motion.
the connecting rod journals (throws)
On a crankshaft, what are the connecting rod journals also known as?
throws
What are the webs of a crankshaft?
the connections between the bearing journals and the connecting rod journals
This crankshaft component is used to balance the rotating mass and is opposite the rod throws.
counterweights
What four things does the design and arrangement of the throws on a crankshaft have on the engine?
- balance of the engine
- amount of vibration
- the loads on the main bearings
- the firing order of the engine
To achieve smooth engine operation, evenly spaced power impulses are required. How is this achieved?
by spacing the engine throws so the engine fires an even number of degrees apart
two-stroke ⟶ 360º ÷ # of cylinders
four-stroke ⟶ 720º ÷ # of cylinders
What are the three main concerns when it comes to crankshaft inspection?
- wear on the journals
- cracks
- cleanliness
How should engine crankshaft journals be measured?
in two positions, 90º from each other
Why is it important to check the fillets of an engine crankshaft during an inspection?
the fillets is to reduce stress areas on the crankshaft;
if they are worn, stress cracks may develop, which can result in failure
Where is the thrust face of an engine crankshaft normally located?
near the flywheel end of the crankshaft
This engine component is used to stabilize the speed fluctuations and store energy during power pulses to carry the engine to the next stroke.
the flywheel
True or false:
The flywheel has a balancing effect on the engine and reduces vibration.
true
What advantageous effect does having heavier flywheel have on an engine?
makes it smoother running
What disadvantageous effect does having a heavier flywheel have on an engine?
slower acceleration ⟶ due to higher friction
Stationary engines typically have timing marks stamped on the outer circumference of the flywheel to aid in checking and adjusting timing. What do these timing marks indicate?
the degrees of crankshaft rotation from when the No. 1 piston is at TDC
True or false:
Engine flywheels can be pinned or blocked to prevent rotation, which makes them a good safety device for large stationary engines.
true
This engine component is used to reduce crankshaft torsional vibration.
vibration balancers
What are engine balancers also known as?
balancers or harmonic balancers
Every time a piston fires, the crankshaft is subjected to tremendous torsional forces which cause the crank to twist or wind up, after which it untwists and set up what is called:
torsional vibration
What happens to a crankshaft if torsional vibration is excessive?
it fails prematurely
What physical property of a crankshaft can be adjusted in order to reduce torsional vibration?
stiffness;
Increasing the stiffness of the crank increases their natural frequency above the running speed of the engine
This engine component acts like a torsional shock absorber.
vibration dampeners
Where are vibration dampeners mounted on an engine?
on the crankshaft, at the opposite end from the flywheel
This type of vibration dampener has a hub, an elastomer (rubber) and an inertia ring on the outside.
rubber-mounted vibration dampener
What type of engine speeds are rubber-mounted vibration dampeners usually found on?
high-speed engines
*also automotive engines
What does it mean if you can grab the OD of a rubber-mounted vibration dampener with your hand and feel movement when you try to turn it?
that it is worn out;
the OD should be solidly fixed to the centre ring
This type of engine dampener consists of a case with an inertia ring inside suspended in a silicone fluid.
viscous-type dampener
What type of engine speeds are viscous-type dampeners found on?
medium- and high-speed engines
When viewing a viscous-type dampener with an IR gun, the ring of the dampener is warmer than the block. What does this indicate?
the it it working correctly;
the friction caused by the ring churning inside of the viscous-fluid should make it warmer than the block
When viewing a viscous-type dampener with an IR gun, the ring of the dampener is cooler than the block. What does this indicate?
the dampener needs to be replaced;
if cooler, it means that the ring inside of the dampener is stuck
This type of dampener is equipped with an internal hub attach to the crankshaft and an internal ring separated by springs.
spring-type dampener
What type of engine speeds are spring-type dampeners found on?
low- and medium-speed engines
Which type of engine dampener is repairable?
spring-type dampener
What must happen if the rubber or elastomer of an engine dampener becomes oil-soaked or torn?
the unit must be discarded
True or false:
Viscous dampeners have a specific service life.
true
This type of plain bearing construction consists of a steel backing on the OD with an intermediate layer of copper, followed finally with an ID of tin or babbit.
tri-metal plain bearings
_______________ ________________ (2 words) is the ability of a bearing to withstand shock loads without flaking or cracking prematurely.
fatigue strength
_________________ is the ability of the bearing to mould itself to the imperfections of the crankshaft journal.
conformability
_________________ is the ability of the bearing to absorb small particles of dirt, thereby preventing damage to the shaft.
embeddability
_________________ ______________ (2 words) is the ability of the bearing to withstand the attack of acids and compounds that are by-products of combustion.
corrosion resistance
_________________ _______________ (2 words) is the ability of the bearing material to move heat, which is created by friction, away from the bearing.
heat transfer
_______________ ______________ _____________ (3 words) is the bearings ability to resist metal transfer under marginal lubrication conditions.
resistance to seizure
_________________ is the bearings ability to maintain an oil wedge.
wettability
What are the two types of plain bearings usually found in bearings?
- sleeve (one-piece)
- shell (two-piece)
This type of engine bearing is one-piece, often called a bushing, and is often used as cam bearings on high- and medium speed engines.
sleeve bearings
This type of engine bearing is a two-piece bearing and is often used on the connecting rods and the main bearings.
shell bearings
- This type of engine bearing must have some method of holding them in place.
- What is used to complete this task?
- shell-type (two-piece) bearings
- tangs or dowels
Bearing ____________ is when the bearing half is wider than the bore that is going to be installed to, and ensures that the bearing doesn’t fall out.
spread
Bearing ____________ is when the bearing inserts are machined to protrude out from the bearing cap and housing and allows for better heat transfer.
crush
What are four common methods used to measure bearing clearance in engines?
- direct measurement
- Plastigage
- lead wire
- bearing lift checks
This method of measuring engine bearing clearance is the most accurate method of checking the bearing clearance.
direct measurement
This method of measuring engine bearing clearance uses a dial indicator and a hydraulic jack.
bearing lift checks
- How should the dial indicator be mounted to measure the main bearing clearances of an engine using a bearing lift check?
- How should the dial indicator be mounted to measure the connecting rod bearing clearances of an engine using a bearing lift check?
- dial indicator mounted on the block reading off the crankshaft
- dial indicator mounted on the crankshaft reading off the con-rod when the journal is positioned at TDC
This method of measuring engine bearing clearances is considered the least accurate, but the most convenient.
bearing lift checks
What is the most common cause of bearing failure in engines?
lack of lubrication;
oil leaks, cold start-ups, dilution, excessive oil consumption, plugged lines, failed oil pump, etc.
What is the second most common cause of bearing failure in engines?
lubricant contamination;
dirt, water, antifreeze, fuel and acids formed from blow-by or fuels
- What effect will there be on the bearing clearances if the shaft supporting bores of a crankshaft are not in alignment?
- What will this do to the bearings?
- the effective bearing clearance is reduced;
- this causes the bearings to overheat and shafts to bend
What tool is used to measure the thickness of old engine bearings in order to compare it to a new bearing?
a ball micrometer