Krukasjournal

Krukasjournal, commonly referred to in English as a crank journal, is the cylindrical bearing surface of a crankshaft that interacts with engine bearings. There are two principal types: main journals, which run in the engine block bearings and support the crankshaft, and crankpin journals (also called rod journals), which connect to the connecting rods and transmit piston forces.

Function: The journals convert the linear motion of the pistons into rotary motion and withstand the dynamic loads of combustion, while allowing smooth rotation. They are finished to precise diameters and surface finishes to support a stable lubricating oil film.

Construction and materials: Krukasjournals are integral parts of the crankshaft, usually made from alloy steels or cast steels. Surfaces are machined and often heat-treated, with fillet radii at the transitions to reduce stress concentrations. Some designs use hardened or coated surfaces to improve wear resistance.

Lubrication and clearance: Journals operate within plain bearings lubricated by engine oil. A controlled bearing clearance and proper oil viscosity maintain a hydrodynamic or boundary oil film that reduces metal-to-metal contact. Clearances are specific to engine type and operating conditions and are monitored during maintenance.

Maintenance and failure: Wear, scoring, pitting, or fatigue can degrade krukasjournals, leading to reduced oil film, loss of balance, and potential engine failure. Inspection involves measuring diameter, roundness, and taper with precision gauges and assessing bearing oil clearance. Damaged journals may require re-machining or bearing replacement.

See also: crankshaft, main bearing, crankpin, connecting rod.