Crankshaft Bearings In Main Engine

Today we will learn about the main engine crankshaft bearing and its location in the main engines on the ship.

The Location

The crankshaft bearings are situated in the transverse girders of the bedplate. Each bearing consists of two identical and replaceable shell halves, the shims to adjust the vertical bearing clearance, the bearing cover and two thrust bolts.

The running surfaces of the bearing shells are lined with white metal. The oil, which is supplied from the engine oil system is forced under pressure through a hole in the bearing cover.

Measurement of Wear

Holes are provided on the collar of the bearing shell through which, with the help of a depth gauge and the measuring bridge, the wear of the running surface of the lower shell can be measured without removing the bearing shell. The measuring bridge and depth gauge are supplied with the standard engine tool set. The original measuring figures from the top of the bridge down to the journal tables.

The bearing shells and covers are marked with same number as the respective bearing saddle.

The diagram below shows the different parts as given in the legend to the sketch

Bearing saddle
Bearing shell
Shims
Bearing shell (identical to 2)
Bearing cover
Thrust bolts
Tie-rods
Column
Crankshaft
Measuring hole
Dowel pin
Main Engine Crankshaft Bearings

Function of Thrust Bearing

The thrust bearing serves to transmit the axial thrust of the propeller to the foundation of the vessel via the bedplate. The thrust bearing is self-adjusting with its design being based on the “MICHELL” principle.

The thrust bearing shaft has flanges forged to both ends, which are connected to the crankshaft and propeller shaft by fitted bolts. The flywheel Is fixed to the thrust bearing shaft by special bolts.

The Thrust Collar

The thrust collar, which is also forged to the shaft, runs between the two bearing the two bearing pads. The pads on the engine side take the axial thrust when the engine is running ahead, whilst the other ones in the flywheel side are used for running “astern”. The pads on both sides are identical in shape.

The running surface of the thrust bearing pads consists of white metal. The pads are submerged in an oil bath, which is constantly being replenished from the engine lubricating system. Thermometers fitted on both sides of the bearing pads can be removed with the aid of a device by turning the crankshaft at the same time.

The two rows of thrust bearing pads extent roughly over 2/3 of the circumference of the thrust ring. The thrust bearing cover projects into the remaining gap keeping the bearing pads from revolving.

Role of the Spacer

The two rows of thrust bearing pads each rest against a spacer. These spacers serve to equalize the axial clearance between the thrust collar of the shaft and the thrust bearing pads, and to adjust the crankshaft axially in relation to the crankshaft bearings.

Lubrication Arrangement

The redial bearings have a separate lubricating oil connection. The shells of the redial bearings are interchangeable between themselves and can be pulled out after the crankshaft respective the flywheel has been jacked up a little.

The lubricating and cooling of both rows of thrust bearing pads are carried out by each inlet for the “ahead” and “astern” pads. The oil flow rate is the same on both inlets. A nozzle is fitted at the lower area of the end of each inlet pipe. Through the overflow (A) and oil bath builds up in the lower area of the pads rows. The outlet of the oil passes over this overflow into the bedplate and from there to the oil tank.

All the above components are shown in figure 2 below