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Issues related to the various driving gears of the valve trains were discussed together with the factors affecting them. The study was focused on the effect of disassembling the toothed pulley shrink-fitted to the crankshaft journal followed by their assembling via pressure fitting. The roughness parameters for surfaces of a new and worn toothed pulley and worn crankshaft journal, and their hardness values were measured. The model for calculations of friction coefficient, contact pressure, and friction torque carried by the contact zone was developed. It was found that the disassembling followed by the assembling of analyzed components can significantly weaken the interference between them. The weakening was accompanied by a decreased contact pressure. The plastic saturation occurred in the contact zone. The corresponding values of the friction coefficient were much higher than those for elastic stress in the contact zone. The friction coefficient values for the plastic saturation conditions differ from each other by up to 10%. Although all values of torque loading the worn toothed pulley exceed values of friction torque carried by the contact zone under plastic saturation, the displacement of the toothed pulley about the crankshaft journal can occur due to possible changes in the friction coefficient in the contact zone. The friction coefficient values can be lowered due to the presence of oxides, impurities, and engine oil droplets introduced into the contact zone by way of the oil mist present inside the engine block.