Connecting rods form the link between the crankshaft and the pistons and transfer the gas and inertial forces to the crankshaft. For the connecting rod to be mounted on the crankshaft, the large connecting rod eye must be divided.
One form of creating this division is "cracking": Cracked connecting rods are initially made as a single-part component. The large connecting rod eye is then broken in two in a targeted manner. The two parts are
screwed together again during mounting. The cracked fracture surfaces achieve an excellent fit precision between the connecting rod shank and the bearing cap.
To prevent a mix-up, the connecting rod shanks and bearing caps that belong together are labelled with an identical pairing number.
- Connecting rod shanks and bearing caps must not be replaced individually or interchanged.
- Only connecting rod shanks and bearing caps with the same pairing number may be used together.
- Connecting rod shanks and bearing caps must not be put down on the fracture surfaces.
- The fracture surfaces must not be reworked, damaged or soiled.
- Prior to mounting, the fracture surfaces must be cleaned with a suitable agent (e.g. brake cleaner) and blown down. Do not wipe down the fracture surface, as fibres and fluff can soil the fracture surface.
- To prevent the fracture surface from becoming soiled, cracked connecting rods may only be transported with bearing caps and with hand-tightened connecting rod bolts.
- It is not possible to overhaul the housing bore, i.e. sanding down the fracture surface and processing the bore is not possible on cracked connecting rods.