crankshaft,main bearings & shaft alignment lesson two

CRANKSHAFT,MAIN BEARINGS & SHAFT ALIGNMENT

LESSON TWO

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. 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. 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 )

1.4 MANUFACTURING

Solid forged built in a single piece ( small-slow speed engines )

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

1.4 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

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

1.4 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

2. MAIN BEARINGS / CRANKSHAFT BEARINGS

2.1 LOCATION

In the transverse saddles of the bedplate.

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. 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 )

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 );

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 );

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 );

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 )

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 )

2.4 PARTS

Upper & lower shells (fitted in bedplate seating / saddle )

2.4 PARTS

Upper & lower shells (fitted in bedplate seating / saddle )

Thrust bolts

Covers

Shims ( for adjusting vertical bearing play )

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 )

2.4 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

2.6.2 Adjustment

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

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

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 )

2.6.2 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 );

Scoring ( striation due to presence of hard particles );

Wiping ( misshaped overlay or white metal due to high temperature )

3. CRANKSHAFT ALIGNMENT

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

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. 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. 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.

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.

3.1.3 Misalignment

Wear of main bearings;

Distortion of engine bedplate transverse members;

Damage to supporting ship’s structure.

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.

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.

3.1.3 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.