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
How are bearings removed for large stationary engines where the crankshaft cannot be removed?
the bearings are rolled out of the bearing saddles
What tool is used to roll bearings out of bearing saddles when the crankshaft cannot be removed?
roll pins;
special pins with a flat heat of predetermined thickness and angle
What needs to be taken into account when rolling in or rolling out a bearing that has a locating tang?
it must be rolled in the proper direction;
What is the cause of more wear on one or more pairs of main engine bearing inserts than the others?
misalignment of the main bearings bores or the crankshaft
When installing bearing shells into an engine for measurement reasons, should you lubricate the bearings?
no;
lubrication can alter measurements ⟶ only lubricate the bearings when it is time for the final installation
True or false:
When installing plain bearings, do not touch the bearing surfaces with your bare finger tips because the oils from them could cause etching of the bearing surface.
true
What method of measurement is used to complete the final bearing clearance check in an engine?
Plastigage
When using Plastigage for final bearing clearance checks, what torque setting should the main bearing caps of an engine be torqued to?
the manufacturers specs
True or false:
Once the main bearing caps are torqued down to manufacturers specs, you should rotate the shaft in order to properly seat the Plastigage.
false;
do not rotate the shaft, as it will make the Plastigage unreadable
When aligning the thrust bearings in an engine, why is it important to not pry against the main bearing cap when prying the crankshaft forward?
doing so will cause the cap and lower thrust bearing insert to become misaligned
When aligning the trust bearings on a crankshaft, how should the main bearing caps be installed?
tightened enough to seat the cap, then backed off one turn
This engine bearing check requires the crankshaft to be pried rearward until the crank thrust cheek seats firmly against the upper thrust bearing insert, followed by prying it forward until the crankshaft thrust cheek seats against the upper thrust bearing at the read.
aligning the trust bearing
*this centres the thrust bearing, but will need to be verified with an end play check
This engine component forms a link that transmits the force of combustion in the cylinder from the piston to the crankshaft.
the con-rod
This engine component is constructed like an I-beam.
the con-rod
Most engine connecting rods have an oil hole drilled through the length of the rod. Why is this done?
to lubricate the piston pin and cool the piston
This type of engine connecting rod has a parting line 90º to the rod beam.
straight cut con-rod
Straight cut con-rods are found on engines with what types of piston arrangements?
in-line and V engines
Bias cut connecting rods are used primarily in in-line engines. Why is this?
the bias cut reduces the width of the rod, allowing it to be removed through the bore
This type of connecting rod is used on integral engines, with the main rod (master rod) being constructed out of a large solid beam that includes the crank end of the rod.
hinged or articulated con-rods
Why is it critical to keep the matched rod and caps of connecting rods as a set, and not mix them up?
the bearing bores will become misaligned;
this are fabricated as a matched set; if they don’t go back together, the misalignment will result in component damage and engine failure
When inspecting an engine con-rod, what test can be completed to ensure that the two bores in the connecting rod are aligned (no twists or bends)?
please the con-rod on a machined surface, and checking for gaps between them with feeler gauges
When replacing the connecting rods in engines, why is it important to ensure that the replacement rods are the same weight as the rods they are replacing?
crankshaft balance;
if the new rods are a different weight, the crankshaft will become unbalanced, increasing torsional stress on the main bearings
- When torquing down bolts, what effect does over tensioning the bolt have?
- When torquing down bolts, what effect does too little tensioning have?
- it weakens the bolt
- allows the bolt to loosen during operation
What are three ways to torque fasteners?
- torque wrench
- torque turn method
- bolt stretch (elongation) ⟶ most accurate
This method of torquing fasteners consists of torquing the bolt to a small prescribed amount to seat the fastener, followed by turning the fastener an additional number of degrees.
torque turn method
This method of torquing fasteners consists of measuring the fastener length before installation, followed by remeasuring the elongation length after installed.
bolt stretch (elongation) method;
this method requires a fastener arrangement where both ends of the bolt can be accessed after installation (no blind holes)
The basic function of this engine component is to receive and withstand the high temperature, high pressure force of the expanding gases caused by combustion.
the piston
What are the two purposes of piston seal in an engine?
- creates a dynamic seal with the cylinder wall
- dissipates heat from the piston to the cylinder wall
Why are the tops of pistons in engines irregularly shaped?
to create turbulence within the cylinder to help mix the air and fuel
*especially in diesel engines
This piston ring groove has small holes drilled around its inside radius.
the oil control ring groove;
the small holes allow oil to drain back into the crankcase
This type of engine piston construction is a one-piece construction and is the most common type of piston due to its simplicity and ease of production.
trunk-type piston
What effect does an air-cooled engine have on the piston clearances compared to a liquid cooled engine?
air-cooled engines will have a larger clearances due to the increased temperature rises
What effect does a longer piston skirt have on a trunk-style piston?
provides more support and quieter operation
Which type of engine piston is known as a crosshead type piston?
two-piece pistons
What are the two parts of a crosshead type piston and what type of materials are they usually made of?
- piston/piston head ⟶ cast iron
- crosshead or skirt ⟶ aluminum
What is the main advantage of a two-piece piston when compared to a one-piece?
wear reduction;
this is due to the reduce wear on the major and minor thrust surfaces ⟶ the aluminum skirt is softer and reduces the likelihood of scuffing the cylinder wall
What component fastens the piston to the crosshead in a two-piece piston arrangement?
the wrist pin (piston pin)
What types of engine speeds are one-piece cast iron pistons found on?
large, slow speed engines
What types of engine speeds are aluminum pistons found on?
medium- and high-speed engines
What are the three main advantages of aluminum pistons when compared to cast iron pistons?
- transmit heat three times faster
- lower weight (1/3 of cast iron)
- fewer tendencies to scuff the liner
What effect does having an aluminum piston vs. a cast iron piston have on piston clearances?
aluminum pistons have to be fitted looser due to the thermal expansion of aluminum (2x that of cast iron)
What is the main disadvantage of aluminum pistons?
softer and melts at a lower temperature
*softer can be both an advantage (less wear on the liner) and a disadvantage (wears more)
What effect does a lack of lubrication have on the top of the piston in an engine?
it will burn holes in the top of the piston
What are the three main methods to supply lubrication to the piston crown for cooling purposes?
- spray nozzle method
- spray through the connecting rod method
- oil circulation through the rod method
Which method of piston cooling and lubrication is commonly used on high speed engines?
spray nozzle method
This method of piston cooling and lubrication has oil sprayed from a nozzle at the underside of the piston.
spray nozzle method
This method of piston cooling and lubrication has oil pumped through the rod lubrication passage to a compartment in the top of the piston.
spray through the connecting rod method
This method of piston cooling and lubrication has oil pumped through the rod to passages in the crown of the piston.
oil circulation through the rod method
Which method of piston cooling and lubrication is commonly used on medium-speed engines?
spray through the connecting rod method
Which method of piston cooling and lubrication is commonly used on very large slow speed diesel engines?
oil circulation through the rod method
This engine component is used to join the piston to the connecting rod, allowing the rod to hinge.
piston pin (wrist pin)
What are the three types of wrist pins found in engines?
- full floating pins
- locked to rod pins
- lock on piston (semi-floating) pins
Which type of piston pin arrangement are known as a semi-floating pins ?
lock on piston pins
- What type of blasting medium should be used when bead blasting engine pistons?
- Where should the bead blasting be limited to?
- glass shot
- the top of the piston and ring land area ⟶ avoid bead blasting the piston skirt
What are the two types of piston rings used in engines?
- compression rings
- oil control rings
Which type of engine piston ring provides a dynamic seal between the piston and the cylinder wall?
the compression rings
Which type of engine piston ring prevent combustion pressures from entering the crankcase?
the compression rings
Which type of engine piston ring prevent lubricating oil from entering the combustion chamber?
oil control rings
What type of engine piston ring cools the piston by transferring heat to the cylinder walls?
both the compression and oil control rings
What type of engine piston ring is self-cleaning?
trapezoidal (Keystone) rings
*this only cleans the ring groove to prevent the ring from becoming stuck ⟶ it does not clean the cylinder wall
This type of piston ring has a trapezoidal shape.
Keystone rings
What seals the compression piston ring in an engine?
the gas pressure from combustion and compression
*this forces it outward and downward to seal
What seals the oil control piston rings in an engine?
the spring pressure from the expansion spring
True or false:
Engine piston rings must sit a little proud of the piston land once installed.
false;
they should fully recede into the ring grooves
Why is the diameter of a ring land on a piston smaller than the diameter of the piston skirt?
to allow for thermal expansion of the piston crown
What are three types of piston ring joints and which one is most common?
- angle joint
- step joint
- butt joint ⟶ most common
How is side ring clearance checked on piston rings?
by measuring the clearance between the ring and the ring land with feeler gauges
What can happen on an engine piston if the ring side clearance is too small?
ring seizure
What can happen on an engine piston if the ring side clearance is too great?
ring breakage and excessive oil consumption
How should piston rings be installed into the cylinder when measuring ring-end gap with feeler gauges?
with a piston;
this ensures that the rings are “squared up”
What can happen to an engine piston if the ring end gap is excessive?
blow-by
What can happen to an engine piston if the ring end gap is too small?
ring binding when the rings are up to temperature
With engine piston rings, what is the rule of thumb for acceptable end gap (if manufacturer specs are unknown)?
0.003” to 0.005” per inch of ∅
OR
0.003mm to 0.005mm per each mm of ∅
6.5” ∅
6.5” x 0.003” = 0.0195”
6.5” x 0.005” = 0.0325”
acceptable gap would be 0.0195” to 0.0325”
When installing piston rings onto an engine piston, how wide should the rings be expanded to get them onto the piston?
only wide enough to get them into place;
expanding them further could distort the ring
How should piston rings in an engine be orientated in relation to one another after installation?
they should be staggered 180º
*that being said, keep in mind that the rings do rotate during operation
True or false:
Never use chrome-faced rings in chrome-plated liners.
true
On an engine piston, if the piston ring has an internal chamfer, the chamfer should be facing:
up;
towards the high pressure side
On an engine piston, if the piston ring has an external channel, the channel should be facing:
down;
away from the high pressure
On an engine piston, if the piston ring has any dots or letting on the ring, these should be facing:
up;
towards the high pressure side
What type of engines sometimes have locating pins for the piston ring gap?
two-stroke engines
*only some, not all
What are two tools used to compress piston rings in order to install them?
- piston ring compressor
- tapered entrance sleeves
Which type of piston ring installation tool is adjustable for various piston diameters?
piston ring compressor
What is mounted onto the flywheel to aid in starting purposes?
a ring gear
True or false:
Crankshafts should be stored by standing them on end, or on a level floor on V blocks for larger crankshafts.
true
Another name for precision inserts used in engines is:
friction bearings
What engine component changes reciprocating motion into rotary motion?
the crankshaft
True or false:
Drilled holes in the an engine’s pistons oil ring groove drains oil back to the crankcase.
true
True or false:
Piston rings in engines should be installed with the dot, notch, or number towards the crankshaft.
false;
Facing up or towards the pressure
True or false:
In engines, piston ring gaps should be lined up one above the other prior to installation.
false;
they should be staggered to reduce leakage
True or false:
In engines, oil control rings depend only on their expanders to maintain contact with the cylinder walls.
true
What are two conditions that would indicate that a vibration dampener would need to be replaced.
- After the specified service life determined by the manufacturer
- If the rubber becomes oil soaked or torn
If an engine was to be driving a fire pump, what component would the pump shaft connect directly to?
the flywheel
Which journals on the crankshaft support the crankshaft and allow it to rotate with minimal friction?
Main journals
Identify the following piston installation tool:
Piston ring compressor
Identify the following piston installation tool:
Entrance sleeve
True or false: Cam ground aluminum pistons measured at room temperature are out-of-round.
True
