The document discusses the crankshaft, main bearings, and shaft alignment. It defines the crankshaft as converting reciprocating motion into rotational motion. The crankshaft is made of throws and journals and experiences bending, shear, and torsional stresses. Crankshafts are manufactured in various ways depending on the engine size and speed. Main bearings are located in the bedplate and made of layered materials to support the crankshaft under pressure lubrication with adjusted clearances.

1. LESSON TWO
Crankshaft, Main Bearings and
Shaf Alignment

2. 1. CRANKSHAFT,MAIN BEARINGS & SHAFT ALIGNMENT

3. 1. CRANKSHAFT,MAIN BEARINGS & SHAFT ALIGNMENT
1.1 DEFINITION OF A CRANKSHAFT

4. 1. CRANKSHAFT,MAIN BEARINGS & SHAFT ALIGNMENT
1.1 DEFINITION OF A CRANKSHAFT
The crankshaft converts reciprocating motion in the cylinder into rotary
motion of the propeller shaft.

6. 1. CRANKSHAFT,MAIN BEARINGS & SHAFT ALIGNMENT
1.1 DEFINITION OF A CRANKSHAFT
The crankshaft converts reciprocating motion in the cylinder into rotary
motion of the propeller shaft.
1.2 PARTS

7. 1. CRANKSHAFT,MAIN BEARINGS & SHAFT ALIGNMENT
1.1 DEFINITION OF A CRANKSHAFT
The crankshaft converts reciprocating motion in the cylinder into rotary
motion of the propeller shaft.
1.2 PARTS
The crankshaft is made up of throws and jurnals. A throw consists a pin (
secured or attached to big / bottom end bearings ) and two webs or
crancks. Jurnals rest or lie in the main bearings.

9. 1. CRANKSHAFT,MAIN BEARINGS & SHAFT ALIGNMENT
1.1 DEFINITION OF A CRANKSHAFT
The crankshaft converts reciprocating motion in the cylinder into rotary
motion of the propeller shaft.
1.2 PARTS
The crankshaft is made up of throws and jurnals. A throw consists a pin (
secured or attached to big / bottom end bearings ) and two webs or
crancks. Jurnals rest or lie in the main bearings.
1.3 STRESSES ( fluctuating )

10. 1. CRANKSHAFT,MAIN BEARINGS & SHAFT ALIGNMENT
1.1 DEFINITION OF A CRANKSHAFT
The crankshaft converts reciprocating motion in the cylinder into rotary
motion of the propeller shaft.
1.2 PARTS
The crankshaft is made up of throws and jurnals. A throw consists a pin (
secured or attached to big / bottom end bearings ) and two webs or
crancks. Jurnals rest or lie in the main bearings.
1.3 STRESSES ( fluctuating )
 Bending ( when the piston is at TDC );

11. 1. CRANKSHAFT,MAIN BEARINGS & SHAFT ALIGNMENT
1.1 DEFINITION OF A CRANKSHAFT
The crankshaft converts reciprocating motion in the cylinder into rotary
motion of the propeller shaft.
1.2 PARTS
The crankshaft is made up of throws and jurnals. A throw consists a pin (
secured or attached to big / bottom end bearings ) and two webs or
crancks. Jurnals rest or lie in the main bearings.
1.3 STRESSES ( fluctuating )
 Bending ( when the piston is at TDC );
 Sheer stress ( in operation );

12. 1. CRANKSHAFT,MAIN BEARINGS & SHAFT ALIGNMENT
1.1 DEFINITION OF A CRANKSHAFT
The crankshaft converts reciprocating motion in the cylinder into rotary
motion of the propeller shaft.
1.2 PARTS
The crankshaft is made up of throws and jurnals. A throw consists a pin (
secured or attached to big / bottom end bearings ) and two webs or
crancks. Jurnals rest or lie in the main bearings.
1.3 STRESSES ( fluctuating )
 Bending ( when the piston is at TDC );
 Sheer stress ( in operation );
 Torsion ( due to speed change, i.e. acceleration & deceleration )

13. 1.4 MANUFACTURING

14. 1.4 MANUFACTURING
 Solid forged built in a single piece ( small-slow speed engines )

17. 1.4 MANUFACTURING
 Solid forged built in a single piece ( small-slow speed engines )
 Semi-built design ( large medium-speed engines ). Crankpins &
webs are forged or cast in one piece and shrunk on to the journals.

18. 1.4 MANUFACTURING
 Solid forged built in a single piece ( small-slow speed engines )
 Semi-built design ( large medium-speed engines ). Crankpins &
webs are forged or cast in one piece and shrunk on to the journals.
 Fully-built ( cast in single piece – webs are shrunk on to the
crankpins and journals

21. 1.4 MANUFACTURING
 Solid forged built in a single piece ( small-slow speed engines )
 Semi-built design ( large medium-speed engines ). Crankpins &
webs are forged or cast in one piece and shrunk on to the journals.
 Fully-built ( cast in single piece – webs are shrunk on to the
crankpins and journals
1.5 MATERIALS

22. 1.4 MANUFACTURING
 Solid forged built in a single piece ( small-slow speed engines )
 Semi-built design ( large medium-speed engines ). Crankpins &
webs are forged or cast in one piece and shrunk on to the journals.
 Fully-built ( cast in single piece – webs are shrunk on to the
crankpins and journals
1.5 MATERIALS
 Carbon steel

23. 1.4 MANUFACTURING
 Solid forged built in a single piece ( small-slow speed engines )
 Semi-built design ( large medium-speed engines ). Crankpins &
webs are forged or cast in one piece and shrunk on to the journals.
 Fully-built ( cast in single piece – webs are shrunk on to the
crankpins and journals
1.5 MATERIALS
 Carbon steel
 Alloy of nickel, chromium & molibdenum

24. 1.4 MANUFACTURING
 Solid forged built in a single piece ( small-slow speed engines )
 Semi-built design ( large medium-speed engines ). Crankpins &
webs are forged or cast in one piece and shrunk on to the journals.
 Fully-built ( cast in single piece – webs are shrunk on to the
crankpins and journals
1.5 MATERIALS
 Carbon steel
 Alloy of nickel, chromium & molibdenum
 Specialy alloyed grey cast steel

25. 1.4 MANUFACTURING
 Solid forged built in a single piece ( small-slow speed engines )
 Semi-built design ( large medium-speed engines ). Crankpins &
webs are forged or cast in one piece and shrunk on to the journals.
 Fully-built ( cast in single piece – webs are shrunk on to the
crankpins and journals
1.5 MATERIALS
 Carbon steel
 Alloy of nickel, chromium & molibdenum
 Specialy alloyed grey cast steel
1.6 ARRANGEMENT OF CRANKS

26. 1.4 MANUFACTURING
 Solid forged built in a single piece ( small-slow speed engines )
 Semi-built design ( large medium-speed engines ). Crankpins &
webs are forged or cast in one piece and shrunk on to the journals.
 Fully-built ( cast in single piece – webs are shrunk on to the
crankpins and journals
1.5 MATERIALS
 Carbon steel
 Alloy of nickel, chromium & molibdenum
 Specialy alloyed grey cast steel
1.6 ARRANGEMENT OF CRANKS
Multi-throw shaft to provide for the engine firing order

27. 2. MAIN BEARINGS / CRANKSHAFT BEARINGS

28. 2. MAIN BEARINGS / CRANKSHAFT BEARINGS
2.1 LOCATION

29. 2. MAIN BEARINGS / CRANKSHAFT BEARINGS
2.1 LOCATION
In the transverse saddles of the bedplate.

31. 2. MAIN BEARINGS / CRANKSHAFT BEARINGS
2.1 LOCATION
In the transverse saddles of the bedplate.
2.2 PURPOSE

32. 2. MAIN BEARINGS / CRANKSHAFT BEARINGS
2.1 LOCATION
In the transverse saddles of the bedplate.
2.2 PURPOSE
To provide support for the crankshaft

33. 2. MAIN BEARINGS / CRANKSHAFT BEARINGS
2.1 LOCATION
In the transverse saddles of the bedplate.
2.2 PURPOSE
To provide support for the crankshaft
2.3 MATERIAL ( multilayer bearings )

34. 2. MAIN BEARINGS / CRANKSHAFT BEARINGS
2.1 LOCATION
In the transverse saddles of the bedplate.
2.2 PURPOSE
To provide support for the crankshaft
2.3 MATERIAL ( multilayer bearings )
Used for crankshaft bearings and connecting rod big end bearings
( 4 stroke engines )

39. 2. MAIN BEARINGS / CRANKSHAFT BEARINGS
2.1 LOCATION
In the transverse saddles of the bedplate.
2.2 PURPOSE
To provide support for the crankshaft
2.3 MATERIAL ( multilayer bearings )
Used for crankshaft bearings and connecting rod big end bearings
( 4 stroke engines )
 Steel support shell ( basic element );

41. 2. MAIN BEARINGS / CRANKSHAFT BEARINGS
2.1 LOCATION
In the transverse saddles of the bedplate.
2.2 PURPOSE
To provide support for the crankshaft
2.3 MATERIAL ( multilayer bearings )
Used for crankshaft bearings and connecting rod big end bearings
( 4 stroke engines )
 Steel support shell ( basic element );
 Bearing metal ( white metal, copper-lead or aluminium-tin alloy,
leaded bronze );

43. 2. MAIN BEARINGS / CRANKSHAFT BEARINGS
2.1 LOCATION
In the transverse saddles of the bedplate.
2.2 PURPOSE
To provide support for the crankshaft
2.3 MATERIAL ( multilayer bearings )
Used for crankshaft bearings and connecting rod big end bearings
( 4 stroke engines )
 Steel support shell ( basic element );
 Bearing metal ( white metal, copper-lead or aluminium-tin alloy,
leaded bronze );
 Nickel barrier ( separating the two layers );

45. 2. MAIN BEARINGS / CRANKSHAFT BEARINGS
2.1 LOCATION
In the transverse saddles of the bedplate.
2.2 PURPOSE
To provide support for the crankshaft
2.3 MATERIAL ( multilayer bearings )
Used for crankshaft bearings and connecting rod big end bearings
( 4 stroke engines )
 Steel support shell ( basic element );
 Bearing metal ( white metal, copper-lead or aluminium-tin alloy,
leaded bronze );
 Nickel barrier ( separating the two layers );
 Galvanized layer ( good running-in and dry running properties )

47. 2. MAIN BEARINGS / CRANKSHAFT BEARINGS
2.1 LOCATION
In the transverse saddles of the bedplate.
2.2 PURPOSE
To provide support for the crankshaft
2.3 MATERIAL ( multilayer bearings )
Used for crankshaft bearings and connecting rod big end bearings
( 4 stroke engines )
 Steel support shell ( basic element );
 Bearing metal ( white metal, copper-lead or aluminium-tin alloy,
leaded bronze );
 Nickel barrier ( separating the two layers );
 Galvanized layer ( good running-in and dry running properties )
 Anti-corrosion layer ( lead or indium )

51. 2.4 PARTS

52. 2.4 PARTS
 Upper & lower shells (fitted in bedplate seating / saddle )

58. 2.4 PARTS
 Upper & lower shells (fitted in bedplate seating / saddle )
 Thrust bolts

59. 2.4 PARTS
 Upper & lower shells (fitted in bedplate seating / saddle )
 Thrust bolts
 Covers

60. 2.4 PARTS
 Upper & lower shells (fitted in bedplate seating / saddle )
 Thrust bolts
 Covers
 Shims ( for adjusting vertical bearing play )

61. 2.4 PARTS
 Upper & lower shells (fitted in bedplate seating / saddle )
 Thrust bolts
 Covers
 Shims ( for adjusting vertical bearing play )
2.5 LUBRICATION

62. 2.4 PARTS
 Upper & lower shells (fitted in bedplate seating / saddle )
 Thrust bolts
 Covers
 Shims ( for adjusting vertical bearing play )
2.5 LUBRICATION
Pressure lubricated ( low pressure )

63. 2.4 PARTS
 Upper & lower shells (fitted in bedplate seating / saddle )
 Thrust bolts
 Covers
 Shims ( for adjusting vertical bearing play )
2.5 LUBRICATION
Pressure lubricated ( low pressure )
2.6 CLEARANCE

64. 2.4 PARTS
 Upper & lower shells (fitted in bedplate seating / saddle )
 Thrust bolts
 Covers
 Shims ( for adjusting vertical bearing play )
2.5 LUBRICATION
Pressure lubricated ( low pressure )
2.6 CLEARANCE
2.6.1 Measurement

65. 2.4 PARTS
 Upper & lower shells (fitted in bedplate seating / saddle )
 Thrust bolts
 Covers
 Shims ( for adjusting vertical bearing play )
2.5 LUBRICATION
Pressure lubricated ( low pressure )
2.6 CLEARANCE
2.6.1 Measurement
 lead wire

66. 2.4 PARTS
 Upper & lower shells (fitted in bedplate seating / saddle )
 Thrust bolts
 Covers
 Shims ( for adjusting vertical bearing play )
2.5 LUBRICATION
Pressure lubricated ( low pressure )
2.6 CLEARANCE
2.6.1 Measurement
 lead wire
 wear gauge / bridge gauge

67. 2.4 PARTS
 Upper & lower shells (fitted in bedplate seating / saddle )
 Thrust bolts
 Covers
 Shims ( for adjusting vertical bearing play )
2.5 LUBRICATION
Pressure lubricated ( low pressure )
2.6 CLEARANCE
2.6.1 Measurement
 lead wire
 wear gauge / bridge gauge
 feeler gauge

68. 2.4 PARTS
 Upper & lower shells (fitted in bedplate seating / saddle )
 Thrust bolts
 Covers
 Shims ( for adjusting vertical bearing play )
2.5 LUBRICATION
Pressure lubricated ( low pressure )
2.6 CLEARANCE
2.6.1 Measurement
 lead wire
 wear gauge / bridge gauge
 feeler gauge
 “ kjaer “ feeler

69. 2.6.2 Adjustment

70. 2.6.2 Adjustment
This can be taken up by reducing the thickness of shims
between the bearing butts and the housing.

71. 2.6.2 Adjustment
This can be taken up by reducing the thickness of shims
between the bearing butts and the housing.
2.7 BEARING DAMAGES

72. 2.6.2 Adjustment
This can be taken up by reducing the thickness of shims
between the bearing butts and the housing.
2.7 BEARING DAMAGES
2.7.1 Indications

73. 2.6.2 Adjustment
This can be taken up by reducing the thickness of shims
between the bearing butts and the housing.
2.7 BEARING DAMAGES
2.7.1 Indications
 increased temperature

74. 2.6.2 Adjustment
This can be taken up by reducing the thickness of shims
between the bearing butts and the housing.
2.7 BEARING DAMAGES
2.7.1 Indications
 increased temperature
 slight oil pressure drop ( sometimes followed by noise )

75. 2.6.2 Adjustment
This can be taken up by reducing the thickness of shims
between the bearing butts and the housing.
2.7 BEARING DAMAGES
2.7.1 Indications
 increased temperature
 slight oil pressure drop ( sometimes followed by noise )
2.7.2 Kinds

76. 2.6.2 Adjustment
This can be taken up by reducing the thickness of shims
between the bearing butts and the housing.
2.7 BEARING DAMAGES
2.7.1 Indications
 increased temperature
 slight oil pressure drop ( sometimes followed by noise )
2.7.2 Kinds
 Squeezing of the overlay / white metal ( problems with oil
film formation );

77. 2.6.2 Adjustment
This can be taken up by reducing the thickness of shims
between the bearing butts and the housing.
2.7 BEARING DAMAGES
2.7.1 Indications
 increased temperature
 slight oil pressure drop ( sometimes followed by noise )
2.7.2 Kinds
 Squeezing of the overlay / white metal ( problems with oil
film formation );
 Fatigue cracking ( due to poor quality, shaft misaligment or
local overload );

78. 2.6.2 Adjustment
This can be taken up by reducing the thickness of shims
between the bearing butts and the housing.
2.7 BEARING DAMAGES
2.7.1 Indications
 increased temperature
 slight oil pressure drop ( sometimes followed by noise )
2.7.2 Kinds
 Squeezing of the overlay / white metal ( problems with oil
film formation );
 Fatigue cracking ( due to poor quality, shaft misaligment or
local overload );
 Dislodgement of overlay or white metal ( due to cracking );

79.  Scoring ( striation due to presence of hard particles );

80.  Scoring ( striation due to presence of hard particles );
 Wiping ( misshaped overlay or white metal due to high
temperature )

82. 3. CRANKSHAFT ALIGNMENT

83. 3. CRANKSHAFT ALIGNMENT
Crankshafts are aligned to determine load reactions on each bearing. This is
done by laser tehnicques and computer calculations.

84. 3. CRANKSHAFT ALIGNMENT
Crankshafts are aligned to determine load reactions on each bearing. This is
done by laser tehnicques and computer calculations.
3.1 CHECKS

85. 3. CRANKSHAFT ALIGNMENT
Crankshafts are aligned to determine load reactions on each bearing. This is
done by laser tehnicques and computer calculations.
3.1 CHECKS
3.1.1 Frequency

86. 3. CRANKSHAFT ALIGNMENT
Crankshafts are aligned to determine load reactions on each bearing. This is
done by laser tehnicques and computer calculations.
3.1 CHECKS
3.1.1 Frequency
 Once a year

87. 3. CRANKSHAFT ALIGNMENT
Crankshafts are aligned to determine load reactions on each bearing. This is
done by laser tehnicques and computer calculations.
3.1 CHECKS
3.1.1 Frequency
 Once a year
 After replacing the main bearing

88. 3. CRANKSHAFT ALIGNMENT
Crankshafts are aligned to determine load reactions on each bearing. This is
done by laser tehnicques and computer calculations.
3.1 CHECKS
3.1.1 Frequency
 Once a year
 After replacing the main bearing
 If the ship has grounded

89. 3. CRANKSHAFT ALIGNMENT
Crankshafts are aligned to determine load reactions on each bearing. This is
done by laser tehnicques and computer calculations.
3.1 CHECKS
3.1.1 Frequency
 Once a year
 After replacing the main bearing
 If the ship has grounded
3.1.2 Techniques

90. 3. CRANKSHAFT ALIGNMENT
Crankshafts are aligned to determine load reactions on each bearing. This is
done by laser tehnicques and computer calculations.
3.1 CHECKS
3.1.1 Frequency
 Once a year
 After replacing the main bearing
 If the ship has grounded
3.1.2 Techniques
The deflections are measured through one revolution of the
crankshaft by inserting a dial gauge / dial indicator gauge
betwee the webs.

93. 3. CRANKSHAFT ALIGNMENT
Crankshafts are aligned to determine load reactions on each bearing. This is
done by laser tehnicques and computer calculations.
3.1 CHECKS
3.1.1 Frequency
 Once a year
 After replacing the main bearing
 If the ship has grounded
3.1.2 Techniques
The deflections are measured through one revolution of the
crankshaft by inserting a dial gauge / dial indicator gauge
betwee the webs.
Measurements are taken at TDC, BDC and two horizontal web
positions.

96. 3.1.3 Misalignment

97. 3.1.3 Misalignment
 Wear of main bearings;

98. 3.1.3 Misalignment
 Wear of main bearings;
 Distortion of engine bedplate transverse members;

99. 3.1.3 Misalignment
 Wear of main bearings;
 Distortion of engine bedplate transverse members;
 Damage to supporting ship’s structure.

100. 3.1.3 Misalignment
 Wear of main bearings;
 Distortion of engine bedplate transverse members;
 Damage to supporting ship’s structure.
3.1.4 Consequences

101. 3.1.3 Misalignment
 Wear of main bearings;
 Distortion of engine bedplate transverse members;
 Damage to supporting ship’s structure.
3.1.4 Consequences
Hogging is closing of the crank throw at TDC.

103. 3.1.3 Misalignment
 Wear of main bearings;
 Distortion of engine bedplate transverse members;
 Damage to supporting ship’s structure.
3.1.4 Consequences
Hogging is closing of the crank throw at TDC.
Sagging is opening of the crank throw at TDC.

105. 3.1.3 Misalignment
 Wear of main bearings;
 Distortion of engine bedplate transverse members;
 Damage to supporting ship’s structure.
3.1.4 Consequences
Hogging is closing of the crank throw at TDC.
Sagging is opening of the crank throw at TDC.
3.1.5 Reports

106. 3.1.3 Misalignment
 Wear of main bearings;
 Distortion of engine bedplate transverse members;
 Damage to supporting ship’s structure.
3.1.4 Consequences
Hogging is closing of the crank throw at TDC.
Sagging is opening of the crank throw at TDC.
3.1.5 Reports
 Main engine crankshaft deflection report;

107. 3.1.3 Misalignment
 Wear of main bearings;
 Distortion of engine bedplate transverse members;
 Damage to supporting ship’s structure.
3.1.4 Consequences
Hogging is closing of the crank throw at TDC.
Sagging is opening of the crank throw at TDC.
3.1.5 Reports
 Main engine crankshaft deflection report;
 Main / auxiliary engine crankshaft deflection record;

108. 3.1.3 Misalignment
 Wear of main bearings;
 Distortion of engine bedplate transverse members;
 Damage to supporting ship’s structure.
3.1.4 Consequences
Hogging is closing of the crank throw at TDC.
Sagging is opening of the crank throw at TDC.
3.1.5 Reports
 Main engine crankshaft deflection report;
 Main / auxiliary engine crankshaft deflection record;
 Crankshaft and engine bearing data sheet.

109. LESSON TWO
Crankshaft, Main Bearings and
Shaf Alignment
(text)

110. The crankshaft, which converts the
reciprocating motion of the piston to rotating
motion, must resist the bending stresses
caused by the connecting rod thrust when the
piston is at top centre.
Then the maximum gas pressure acts straight
down on the crankpin and tends to bend the
shaft between the adjacent bearings. The
crankshaft must also withstand the torsional
forces produced by the change of speed.

111. Complete the sentences
• The crankshaft converts ... ... to .... ....
• It must resist the bending stresses caused by
the connecting rod thrust when ... ... .
• Then the maximum gas pressure acts straight
down on the crankpin and tends to ... ....
• The crankshaft must also withstand the ... ....

112. Lesson Two
Crankshaft, Main Bearings and Shaf
Alignment
(text)

114. Medium speed engines have crankshaft usually
solid forged, i.e. made from a single piece,
while slow speed engine crankshafts are mostly
of semi-built design with crankpins and webs
forged or cast in one piece and shrunk on to the
journals. The type of steel used, which is
carbon or alloy steel containing nickel, chromium
and molybdenum, is chosen for its strength,
resistance to fatigue and hardness of bearing
surface.

115. • Medium speed engines have crankshaft usually
solid forged, i.e. made ... ...,
• Slow speed engine crankshafts are mostly of
semi-built design with ... ...
• They are ... or ... in one piece and ... on to the
journals.
• The type of steel used for crakshafts is ... ...
• It contains nickel, ... and must be resistant to ...
....

116. The cranks of a multi-throw shaft are set at
appropriate angles giving a “firing order” for the
engine. The firing order is chosen primarily to
obtain a smooth torque and the best mechanical
balance. However, main bearings loads, exhaust
arrangements suitable for turbocharging and
torsional vibration may also be taken into
account. Although the crankshaft appears to be
robust, they rely on the main bearings to
develop their full strength.

117. • cranks of a multi-throw shaft are set at
appropriate angles giving ... ...
• The firing order is chosen primarily to obtain ...
... and ... ...
• However, we must also take ito account:
– ... loads,
– exhaust arrangements suitable for ... and
– ... ...
• Crankshaft rely on the ... ... to develop their full
strength.

119. When a crankshaft has to be handled
outside the engine, it should be carefully
supported to avoid high bending moments
on it by its own weight. In the engine it is
essential to ensure that the bearings
carrying it are in good alignment, as
bearing misalignment will cause the
crankshaft to bend and eventually break
it.

120. When a crankshaft has to be handled
outside the engine, it should be carefully
supported to _____ high bending
moments on it by its own weight. In the
engine it is essential to ensure that the
bearings carrying it are in ______
alignment, as bearing misalignment will
______ the crankshaft to bend and
eventually break it.

122. The main bearing shells are made of steel with
a lining of bearing metal which can be white
metal, copper-lead or aluminium-tin alloy. A thin
flash of lead or indium is often added to provide
a layer giving protection against corrosion. The
shells are held in position and shape by
seatings of the bedplate or frame.To ensure
efficient and reliable operation the crankshaft
should be checked periodically for alignment by
measuring the deflection of the webs.

123. The main bearing shells are made ... steel with
a lining ... bearing metal which can be white
metal, copper-lead ... aluminium-tin alloy. A thin
flash of lead or indium is often added ... provide
a layer giving protection ... corrosion. The shells
are held ... position and shape by seatings of
the bedplate or frame. ... ensure efficient and
reliable operation the crankshaft should be
checked periodically ... alignment by measuring
the deflection ... the webs.

124. QUESTIONS AND DISCUSSION
1. State the function of the crankshaft.
2. What forces is a crankshaft subjected to?
3. What kind of crankshafts arer used in: a) Medium speed diesel
4. Slow speed diesel
5. 4. What does the choice of steel type for crankshaft depend on?
6. What is the “firing order”?
7. What else is taken into consideration in designing a crankshaft?
8. Why should special care be taken when handling crankshafts outside the
engine?
9. How are the main bearing shells protected from corrosion?
10.How are crankshafts positioned in the engine with respect to their
connection to the shaft?
11.What is a journal bearing? What other types of bearings do you know?
12.What is the function of the webs?
13.How are the main bearings examined for possible wear?

125. Test
CRANKSHAFT, MAIN BEARINGS AND
SHAFT ALINGNMENT

126. • The crankshaft, which converts the _________ motion of the piston
to rotating motion, must resist the _________ stresses caused by
the connecting rod _________ when the piston is at top centre.
• Then the maximum gas pressure acts straight down on the
_________ and tends to bend the shaft between the adjacent
_________ . The crankshaft must also _________ the torsional
forces produced by the change of speed.
• Medium speed engines have crankshaft usually solid _________ ,
i.e. made from a single piece, while slow speed engine crankshafts
are mostly of semi-built design with crankpins and _________
forged or cast in one piece and shrunk on to the _________ . The
type of steel used, which is carbon or alloy steel containing nickel,
chromium and molybdenum, is chosen for its strength, resistance to
_________ and hardness of bearing surface.