Tie rods or Tie bolts.
To understand the role played by tie rods, it is necessary to appreciate what is happening inside the cylinder of the engine. When the piston is just after the top dead centre (TDC), the pressure inside the cylinder can rise as high as 140 bar. This acts downwards through piston rod and connecting rod, pushing the crankshaft down into the bearing pockets. At the same time, the pressure acts upwards trying to lift the cylinder head.