Contribution of Oil Traction to Diesel Engine Cam Galling

Heavy Duty diesel engines typically use roller followers in contact with the cam to reduce friction and accommodate high Hertzian stresses. When the rolling contact slips into sliding, cam galling can occur that may lead to major cam failures. Oil traction has been identified as a possible source to cause slipping. In this study, oil traction was first measured in a Mini Traction Machine (MTM). The results were then validated by a series of engine tests to show that the measured oil traction correlated with the occurrence of cam galling. Finally, the MTM was used to evaluate various engine oil formulations. It is concluded that some advanced base oils, if not properly compensated by the additive package, exhibit dangerously low oil traction. Oil traction needs to be part of the oil formulation considerations.