Mercedes-Benz Group Media - A-Class; The state-of-the-art, lightweight crank assembly in the petrol engines consists of an aluminium crankcase with cast-iron cylinder liners. Valve timing is taken care of by a hollow-bore camshaft made from induction-hardened forged steel and low-friction roller cam followers. A timing chain with a hydraulic tensioner and rubber-coated sprockets drives the camshaft. Hydraulic valve clearance compensation takes place automatically.