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CRANK SHAFT &VIBRATION DAMPER

By-G.N.Singh,

Asst.Prof.(D)/IRIMEE

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CRANKSHAFT Engine Crank Shaft is the single costliest Item in

Diesel Engine [Rs.16.0 Lakh (approx.)] Transforms reciprocating motion to rotary motion Crankshaft may be ‘assembled’ type or 2 pieces bolted

together or in single piece forging. ALCO 16 Cylinder ‘V’ type Engine is made of one

piece of forged steel alloy , with its main bearing journals and crankpins machined to a high degree of smoothness.

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CRANKSHAFT MOUNTED ON VEE BLOCKS

CRANKSHAFT

No of Crank Pins: 8 NosNo of Main Journals: 9Centre Journal: 5Lift crank shaft at Crankpins: 2 & 7Support crankshaft at Main Journals: 3&7

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Crankshaft is slung under Cylinder Block and rotates on the Main Bearing (Shells). It is supported by Bearings Caps that are mounted to Saddles in the Block with stud bolts and nuts.

Main bearings and Crankpins of Crankshaft joined by a series of crankshaft webs, to which counterbalances are welded at intermittent locations for balancing purposes.

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Two Con. Rods (right and left bank of same Cylinder) are mounted side by side on each of the Shaft’s Crankpin. The shaft is so designed that every two symmetrically opposite pins have the same radial throw position.

Crankshaft gear, which drives the shaft and Camshaft gears, is applied to the ‘power take-off end’ of the shaft.

Free end of the shaft provides drive for the Engine’s Cooling Water and Lubricating oil Pumps

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Crankshaft forms an integral part of Engine’s Lubricating system. A continuous flow of oil passes under pressure from the main lubricating oil header in the Engine’s Base to the bearing cases and bearing ; through drilled passages in the shaft and to Crankpins and on Connecting rod bearings.

Oil slingers and Catchers are provided at both ends of the shaft to prevent oil leakage.

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Crankshaft end thrust is restricted by the use of either

(a) individual thrust collars, installed in both sides of the centre main bearings saddle

(b) an upper main thrust bearing shell or upper and lower main bearing thrust shells located at the journal nearest to the power take-off end of the shaft.

All shells, thrust or otherwise , are of the lead-tin overlay and are suitably strengthened by a Steel backing.

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Location Data :

16 Cylinder Engine Crankshaft:

No of Main Bearings : 9

Location of Centre Journal : 5

No. of Crankpins : 8

Lift Crankshaft at Crankpin Nos. : 2 and 7

Support Crankshaft at Main Journals: 3 and 7

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Removal :

• Remove Driven equipment and Oil catcher from power take-off end of engine.

• Remove all Engine parts for facilitating removal of Cylinder Block from base and crankshaft from Cylinder Block.

• Check amount of Crankshaft Thrust to determine replacement of thrust bearing.

• Remove nuts and washer from stud bolts and lift off bearing caps and shells.

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Note : • Tag each cap and shell with proper location since

they are not interchangeable.• Removal of thrust bearing before lifting crankshaft

is mandatory since bearing face may be damaged otherwise.

• Use suitable Sling and Lifting Blocks attached to Crankpins. Crankshaft to be lifted and placed in clear and well protected area.

Apply grease and wrap all journals and Crankpins with suitable protective non-corrosive material if shaft is not to be reinstalled within short time.

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Manufacture : Material : Chrome – Molybdenum Steel 9 Equivalent to

SAE 4140) Process of forging is such that continuous grain is

maintained. Sequence of operation for Manufacture :

a) Forging and forming operationb) Rough Machiningc) Drilling of oil Holed) Ultrasonic and Mechanical Testinge) Welding of Counter weights and X-Ray Testf) Stress Relieving and Shot Blastingg) Final Machining and giving fillet radius at Crank

journal corners and making oil holes. h) Nitridingi) Grading lappingj) Static and Dynamic Balancingk) Final Inspection.

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Note : There are 2 processes for surface hardening :

Note : 1. For low HP Engine, Induction hardening is preferred

as case depth more and crank journal/main bearing journal can be ground down to next step size.

2. For high HP and high speed Engines, nitriding process is preferred as it gives long life and rate of wear being negligible.

Method Hardness Depth of Hardness

Induction Hardening

C-40 0.124”

Nitriding C-60 0.012”-0.015”

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Inspection and Maintenance : Clean Main Bearing journals and Crankpins with fuel oil.

Clean lube oil passages and flush. Dye penetration/Magnaflux testing conducted to detect

surface cracks. Inspect Main Bearing journals and crankpins for excessive

roughness and burrs.

Note : Surface finish of 25 RMs or lower (Measured by Profilometer etc.) considered satisfactory.

Check alignment of MB Saddle bores by placing straight edge along bottom of all Saddles.

Examine thrust bearings for signs of wear.

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Measure following Dimensions :

1. Crankpin :

Position crankshaft vertically to check dimensions at two locations just beside two oil holes (at two right angular planes in each location) to check Ovality and Taper.

Diameter : 5.998- 6.000” (New)

: 5.996” (Limit)

Out-of-Roundness : 0.002”(Limit)

Taper : 0.001”(Max)

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2. Main Bearing Journal :

• Position Crankshaft keeping No. 1 Crankpin in vertical location

• Measure horizontal and vertical diameters

• Horizontal diameter should be close to original size.

• Vertical diameter should be smaller but not less than specified limits.

• Difference between Horizontal and Vertical measurement is Main bearing journal out of roundness

Diameter : 8.498 - 8.500”(New)

: 8.496”(Limit)

Out of roundness : 0.002”

Run out : 0.004” (0.008” Total Run out)

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3. Fillet Radius :

• Checked through special Gadget.

• 0.0005” Feeler gauge should not pass between the gadget and Fillet.

4. Crankshaft Run-out :

• Support Shaft on V-Blocks on Surface Plate

• Using Dial Indicator on Horizontal Plain at Centre of each Journal (oil groove Path), check Run-out.

Run-out : 0.002”(Limit)

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4. Eccentricity Checking :

• Eccentricity checked between any three consecutive Main Bearing Journals (1,2,3 etc.) is given by the distance between center line point of middle (second) journal and mid-point of imaginary line joining centre points of first and third journals.

• Eccentricity : 0.0001” Note : Support crankshaft on ‘V’ Blocks and

measure run out of middle of three consecutive journal using Dial Indicator.

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Installation :

• Crankshaft to be installed with Cylinder Block in inverted position

• Install all upper bearing Shells in saddle except thrust bearing shell.

Note: Ensure all bearing locks are properly located in saddle bearing recesses.

• Apply Split gear to Crankshat ( if previously removed)

• Attach suitable Slings and lifting Block to crankpins for lowering Crankshaft into Cylinder block Saddle.

• Thrust Bearing Shell should be rolled in. Thrust bearing should be installed after crankshaft is in place to prevent crushing of bearing face.

• Apply lower Bearing Shells and Caps.

• Check Crankshaft Thrust.

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Reapply Cylinder Block to Base Reapply Crankshaft Extension shaft and parts previously

removed. Reconnect all piping. Reapply Oil catches and driven equipment to power-take-off

end of Engine. Check Crankshaft deflection.

Checking Crankshaft Thrust: At location other than thrust bearing use, pinch bar between

bearing cap and crankshaft web to pry crankshaft forward and backward.

Measure clearance between thrust face and crank web.Note : Do not pry against cap where thrust bearing is

located since this may damage thrust pads.

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Crankshaft Deflection :

•Position Deflection Gauge at centre punch marks between webs of crankpins nearest to power take-off end of crankshaft. making sure Gauge is parallel to crankshaft in horizontal and vertical planes.

•Rotate clockwise and counter clockwise to limits determined by Connecting rod interference.

• Correcting Deflection : Fixed shims are welded in place of bottom bolting pads of

generator. Limited shims of less than 0.090” thickness are used at the top bolting pads.

Permissible limit of deflection : ± 0.0008” (on each side)• If readings on dial indicator exceed max. allowable limits,

apply or remove Shims at the top generator pads until deflection is within limits.

CRANK WEB DEFLECTION

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GEN MOUNTINGS

BLOCK MTG

BASE MTG

ADJUSTABLE SEAM

FIXED SEAM

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Note : Shims of magnet frame with the base are fixed and ` normally not disturbed during crankshaft deflection.

CHECKING CRANKSHAFT DEFLECTION WITH GAUGE

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Crankshaft Clearance Data

(a) Main Bearing Journal New Limit

Diameter 8.498-8.500” 8.496”

Out- of-roundness - 0.002”

Run out - 0.004”

(0.008” Total run out)

Eccentricity - 0.001”

(b) Crankpin

Diameter 5.998-6.000” 5.996”

Out- of-roundness - 0.002”

(C ) Crankshaft Thrust

Using Bearing Shell 0.010-0.017” 0.035”

Using Thrust Collars 0.012-0.021” 0.030”

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Crankshaft Split Gear:Description :

• Crankshaft Gear for 251 Type Engine is mounted at Power- take-off end of Crankshaft and meshes with Camshaft Gear.

•Made in 2 halves of hardened steel and accurately fitted and keyed to the crankshaft.

•Gear is held in place by 4 bolts and has locating dowel to position the halve as they are assembled.

•Gear is 4 pitch straight Spur type.

Note:

•Spilt Gear is statically balanced and halves are not interchangeable

•Replacement must be in matched pairs.

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CRANKSHAFT SPLITGEAR

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Note :

Metal to Metal joint formed by both halve of gear to be checked using Feeler Gauge.

It should not be possible to insert Feeler gauge more than 1/4”.

Split Gear Clearance and Torque :

1.Crankshaft key

2.Interference fit : 0.0000 – 0.0005”

3.Gear side Clearance : 0.007” – 0.0025”

4.Split line Clearance : 0.0015”

5.Gear Cap screw Torque :

Preliminary : 50 ft.lbs

Final : 300 ft.lbs

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CAPSCREW TIGHTENING SEQUENCE

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Crankshaft Drive Assembly – Free end

• Extension Shaft assembly is located at free end of engine crankshaft and is used for auxiliary power take-off

• Major components are :

Extension Shaft

Oil Seal

Drive Gear

Vibration Damper

Extension Shaft :Has oil passages drilled in to supply oil to Vibration Damper.

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Extension Shaft

EXTENSION SHAFT

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SECTIONAL VIEW OF VIBRATION DAMPER

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Extension Shaft Oil Seal

Oil Seal consists of :

• Slinger (Grooves and Peaks) machined into the extension shaft.

• Oil Catcher, which fits closely around the shaft to collect oil flowing out of free end of engine and return it to crankcase.In the assembly, seal is used to supply oil to Vibration Damper.

• Crankshaft oil hole is plugged and pressurized oil flows from inlet hole in Catcher , through a Floating bushing, into oil passages in Ext. Shaft and into Chamber in the Centre of Vibration Damper.

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Drive Gear :

• Drive Gear used to rotate LOP and WP.

• Spur type gear is pressed into Extension Shaft and held in place by Capscrews extending through Vibration Damper and into Crankshaft flange.

Vibration Damper :

• Vibration Damper is of hydraulic , Paddle wheel type, in which some of vibration energy is absorbed by work done in forcing Engine lubrication oil through narrow passages.

Continuous circulation of oil provided in Damper either by passages through Oil Seal and Ext. Shaft.

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• Parts :

Spider (with external spur teeth)

Intermediate Ring (with internal spur teeth)

Outer Rings (Side plates) [2 Nos.]

( To secure the parts with bolts and nuts)

• Oil flows from chamber in centre of the damper through radial holes, beginning in spider hub and ending in passages at spider hub which is much smaller than the remainder and provides oil flow restriction.

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SPIDERSPIDER AND INTERMEDIATE RING ASSEMBLED

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• Spider is designed so that each tooth is directly supplied with oil.

An auxiliary circumferential oil groove is machined into each side face of spider to supply oil for rubbing surfaces between spider and outer ring. These grooves are supplied by means of passage connecting grooves of radial holes.

• Intermediate ring is ground on both sides to uniform thickness, slightly thicker than Spider.

This difference in thickness permits axial clearance necessary for proper oil passage.

Intermediate Ring ‘floats’ on tips of Spider Teeth

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• 4 vent holes drilled through rim of Intermediate Ring to the fillets of internal spur teeth in order to relieve oil pressure and re-adjust ring to a central position when it becomes displaced.

The holes , which are equally spaced around the ring are normally covered by tips of Spider teeth. However, oil is permitted to vent when intermediate ring becomes displaced and spider teeth no longer cover the hole thereby reducing pressure.

The higher pressure on opposite side of each tooth then prevails and restores intermediate ring to its correct position. This design used to prevent sudden bumping of teeth.

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• 2 identical Outer rings (Side plates) are secured to Intermediate ring by means of through bolts.

Rings have been made fairly thick to add considerable fly wheel effect.

Inner face of rings adjacent to Spider are covered with oil which is continuously flowing the clearance and escaping to Crankcase.

Note :

Examination of Vibration Damper

1. Remove crankcase doors nearest damper and oscillate it about 10º each way by pressing against outer ring bolts. If Damper cannot move, it may have become scored or jammed.

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2. Extn. Shaft has oil passage drilled to supply lube oil to Vibration Damper. Hole in the centre of crankshaft should be plugged.

3. Extension shaft Run-out : 0.006” max.

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CHECKING EXTENSION SHAFT RUN-OUT

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CAMSHAFT GEAR

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