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 usually is also necessary to machine the two neighbouring main journals as well.