Severe bearing failures with sharp temperature rises and falls may result in the formation of so-called “hard spots”. The presence of hard spots in a crankshaft is very undesirable because it leads to uneven wear (cam effect) and because there is an increased risk for cracks to develop over time.

Depending on the engine type and maker, the hardness of the crankshaft typically has to be lower than approximately 450 HB. For critical areas where stresses are higher, such as around the oil bore and fillets, a maximum of around 350 HB is usually specified. If the crankshaft hardness is higher following a bearing failure, then in-situ heat treatment (annealing) may be the only way to save the crankshaft.

The following picture shows a very good example of a crank pin that has undergone severe hardness changes due to overheating. The picture was taken after the pin was machined to a diameter of – 2.90 mm. The shiny areas that indicate a very high hardness are easy to see. Such a pin requires heat treatment if the crankshaft is to be saved.

QuantiServ has gained considerable experience with this process and has been able to bring down the hardness on dozens of crankshafts so that they could be saved.

Crankpin
Crankpin
Hard spots on a crankpin, until 581 HB in this case
Hard spots on a crankpin, until 581 HB in this case
Resistance heating elements installed
Resistance heating elements installed
Crankpin covered in insulation material during the heat treatment process
Crankpin covered in insulation material during the heat treatment process

Image Gallery

Crankpin with unacceptably high hardness of over 600 HB, prior to annealing
Crankpin with unacceptably high hardness of over 600 HB, prior to annealing
Crankpin prepared for annealing. The heat is provided by resistance heating pads
Crankpin prepared for annealing. The heat is provided by resistance heating pads
Crankpin during in-situ annealing
Crankpin during the process of in-situ annealing
Control unit that tightly and accurately controls the correct temperature rises and falls
Control unit that tightly and accurately controls correct temperature rises and falls
The same crankpin after annealing, hardness reduced to a maximum of 391 HB
The same crankpin after annealing, hardness reduced to a maximum of 391 HB
Another pin on another engine type during annealing
Another pin on another engine type during annealing