SI 1171
For technical personnel only!
1/2
SERVICEINFORMATION
DAMAGE TO CRANKSHAFTS …
… CAUSES AND THEIR PREVENTION
01 02 03 Flywheel side/
power output
04
08 07 06 05
01 Hardness zone 03 Oil bore 05 Conrod journal 07 Counterweights
02 Crank web 04 Stroke x 2 06 Main bearing journal 08 Stud
PREPARATIONS FOR AN EXTENDED CRANKSHAFT SERVICE LIFE BEGIN AT INSTALLATION
01 04
• Correctly remedy any pre-existing damage on the main
bearing centre line and on the connecting rods.
• Insert the crankcase bearing shells and the bearing cap.
Always bear in mind the continuity and cleanliness of the oil
bores as well as the diameters of the main bearing and
conrod journals.
• Thoroughly clean the oil ducts in the crankcase using 02 05
compressed air.
• Thoroughly oil the sliding surfaces of the bearing shells with
approved oil.
• Fit the main bearing caps. Always note the numbering of the
main bearing caps. Slightly oil the main bearing screws and
© MS Motorservice International GmbH – EN – 05/12 (022020)
tighten to the prescribed tightening torques.
• Check that the crankshaft runs free. Check the axial play of 03 06
the crankshaft and adjust if necessary.
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OUR HEART BEATS FOR YOUR ENGINE.
SI 1171
For technical personnel only!
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THE CAUSE OF BROKEN CRANKSHAFTS IS RARELY MATERIAL FATIGUE BROUGHT ABOUT BY EXTENDED USE
Far more frequently, broken crankshafts can be attributed to:
• Mechanical overload of the crankshaft through abnormal
combustion, water hammers, etc.
• Sudden jamming of the engine due to a faulty gearbox,
loose counterweights, etc.
• Excessive rotary oscillation, e.g. faulty vibration dampers,
faulty flywheels or couplings.
• Material weakening due to previous bearing damage or
annealed bearing journals, etc.
• Unreliable modification work to the crankshaft bearing.
• Mechanical damage to the shaft before installation.
INSTALLATION FAULTS AND WEAR ARE THE MOST COMMON CAUSES OF DAMAGE TO THE CRANKSHAFT AND
CRANKSHAFT BEARINGS
• Softening of the bearing journals due to previous bearing • Following bearing damage, swarf was left in the engine-oil
damage or improper modification work, e.g. excessive circuit.
regrinding. • The oil cooler, engine oil and oil filter were not replaced.
• Use of incorrect bearing shells, e.g. normal three- • The bore diameters of the crankshaft bearings in the
component bearings instead of sputter bearings, incorrect crankcase were not checked or repaired following pre-
or missing oil bores. existing damage.
• The prescribed bearing clearance was not adhered to. • Main bearing/conrod bearing cap were mixed up or installed
Causes: worn or warped crankcase, oversized or undersized twisted.
bearing journals or errors in geometry such as conical or • Incorrect tightening torques and/or old bearing cap screws
spherical bearing journals. were used.
• Lubricating oil deficiency on commissioning as the oil • The manufacturer’s specifications were not followed on
system was not filled with oil and compressed beforehand. engine commissioning.
TIPS AND TRICKS FOR EXTENDING THE SERVICE LIFE OF YOUR CRANKSHAFT
• Adequate oil quantity in the engine (in accordance with valve, faulty injector nozzles or oil filter housing, blocked
manufacturer’s specifications). lines and ducts, etc.).
• Correct oil specification, do not use c ontaminated or old oil. • Prevent high engine-oil temperatures as these may cause
• Avoid contaminating the engine oil with coolant or fuel. the lubricating film to rupture.
• Prevent faults in the oil circuit that could lead to oil-pressure
problems (e.g. faulty oil pump, faulty oil pressure relief
© MS Motorservice International GmbH – EN – 05/12 (022020)
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The right of changes and deviating pictures is reserved.
OUR HEART BEATS FOR YOUR ENGINE.
