When a  four-stroke engine crankshaft has suffered from an overheated crankpin or main journal, then it may be that the crankshaft buckled under the influence of the thermal stresses that were induced by the bearing failure. A trueness check of the crankshaft will reveal if the crankshaft suffered from buckling.

If so, then it is often possible to straighten the crankshaft in-situ, without removing it from the crankcase. This process is known as “peening” and is a cold process, whereby a small force is applied to the correct places repeatedly to bring the shaft back to its original straightness. QuantiServ’s technicians are very experienced in this process and have been able to straighten many four-stroke crankshafts, thereby saving them.

Three examples of crankshaft run-out measurements (clocking tests) before and after peening, with measurements recorded in mm:

A 52-bore engine in Indonesia,
main journal #7:

Crank Angle Position Before Peening After Peening
0 0
90° +0.14 +0.02
180° +0.32 +0.03
225° +0.34 +0.04
270° +0.23 +0.02
360° 0 0

A 46-bore engine in Indonesia,
main journal #6:

Crank Angle Position Before Peening After Peening
0 0
90° +0.16 -0.01
180° +0.23 +0.02
270° +0.05 +0.01
360° 0 0

A 40-bore engine in Mauritius,
main journal #7:

Crank Angle Position Before Peening After Peening
0 0
45° -0.28 -0.01
90° -0.09 -0.02
180° +0.10 +0.02
270° +0.25 +0.03
360° 0 0

After peening, the affected crankpin must be machined and under-size bearings must be installed. If the crankshaft deformation was severe, then it may in exceptional cases be necessary to machine the two neighbouring main journals as well.

Case Studies

A straightness check carried out by QuantiServ’s in-situ specialists in response to a crankpin bearing failure on a 12-cylinder, 40-bore crankshaft installed on a Dutch-owned dredger revealed that the crankshaft had lost its original straightness. A clocking test showed a run-out of 0.18 mm, which is beyond acceptable limits.

Our specialists carried out in-situ peening, which took one day and brought the crankshaft back to an acceptable run-out of 0.03 mm. The crankshaft was then machined and polished to a final diameter of -7.00 mm.

Straightening (peening) the crankshaft
Straightening (peening) the crankshaft
Machining of the pin to under-size
Machining of the pin to under-size
Surface roughness measurement after polishing
Roughness measurement after polishing