Since high engine speeds, high compression forces and high temperatures exert extreme loads on the crankcase, the crankcase is very compact in its design and dimensions and built as a very stiff bedplate structure, a concept which has already proven its qualities in motorsport. Made of die-cast aluminium, the bedplate features grey-cast-iron inlays ensuring very precise support of the crankshaft. In particular, this structure keeps main bearing play throughout the entire range of operating temperatures within close limits, the grey-cast-iron inlays reducing thermal elongation of the aluminium housing. As a result, oil flow remains almost unchanged at all times. And to form a positive engagement with the aluminium frame, the inlays have open cut-outs integrating them directly in the frame.
With the distance between cylinders measuring only 98 millimetres or 3.86, the crankshaft made of forged, high-strength steel is relatively short, making it very stiff in terms of flexural and torsional strength and reducing the weight of the crankshaft to just 20 kg or 44 lb. Running in five bearings, the crank-shaft has a main bearing measuring 60 millimetres or 2.36 in diameter, with bearing width of 28.2 millimetres or 1.11. In each case two connecting rods act on one of the four crankpins offset from one another by 90.
Lightweight construction specifically on all moving masses.
The weight-optimised box-type pistons are cast out of a high temperature-proof aluminium alloy and coated with iron. This reduces their weight to a mere 481.7 grams including the piston pins and rings. Compression height is 27.4 millimetres, with a compression ratio of 12.0:1.
The pistons are cooled by oil spray jets connected to the main oil pipe. Measuring 140.7 millimetres or 5.54 in length, the cracked trapezoidal connecting rods are made of a high-strength steel-magnesium alloy. Including the bearing shells, each connecting rod weighs just 623 grams, which significantly reduces the oscillating masses.
The single-piece aluminium cylinder heads feature four valves per cylinder in characteristic BMW style. The valves weighing 42 grams each are activated by ball-shaped cup tappets with hydraulic valve play compensation. Tappet diameter is only 28 millimetres or 1.10, while the intake and exhaust valves measure 35 and respectively 30.5 millimetres (1.38 and 1.20) in diameter. Measuring only 5 millimetres or 0.20 across, the valve shaft has hardly any influence on flow conditions in the intake manifold, while the hydraulic valve play compensation rules out any change in valve play, ensuring lasting reliability and at the same time reducing the cost of maintenance.
The engine always keeps a cool - cylinder - head.
Compared with conventional systems, the cross-flow cooling concept featured on the new V8 power unit significantly reduces pressure losses in the cooling process, spreading out temperatures smoothly and consistently throughout the cylinder head and thus reducing temperature peaks at all critical points. To ensure a perfect flow of cooling around each cylinder, the coolant flows from the crankcase via the exhaust side crosswise through the cylinder head and the collector rail on the intake side to the thermostat and, respectively, to the radiator. ...next page >>