Roller bearing instead of sliding bearing for the future
Leaving the two-stroke engine out of the picture for a moment, the sliding bearing crankshafts are numerically by far superior compared to the roller bearing crankshaft. This does not necessarily have to stay this way. There are, indeed, efforts to insert roller bearings into the crankshaft and to overcome the disadvantages regarding the lubrication. The assembly does not have to be changed as it is also possible to break roller bearings calculatedly and mount it in two halves. Clear advantage would be a lower friction loss.
Babbitt metal bedding-in layer, diffusion barrier run layer
We go back to the current reality. The picture displays bearing shells consisting of materials that become softer, going from inside to outside, starting with bronze as a substratum up to the babbitt as a bedding-in layer. You may also speak of the 3 layer bearing with thicknesses of approx. 0.2 mms outside to 0.02 mms inside. The copper of the substratum often gleams through on the crankshaft. Also the layman may thus detect a higher running performance or a defect. A holding nose prevents that both halves turn. The oil bore flows into a groove that runs around and distributes the oil steadily on the bearing and via another drilling to the big-end bearings.
A specific feature is the flanged bearing. There is just one, and it is mostly situated on the flywheel side or in the middle. To be able to take up the axial forces of the crankshaft, it has a collar on both sides which corresponds, actually, to an axial bearing shell. The collar does not always have to be connected solidly (as in the picture on top) with the bearing shell. Thus a complete flanged bearing may be made up of up to six parts.
Determining the clearance with a dial gauge
Picture 3 shows a dial gauge for the determination of the axial clearance of the crankshaft. It must be solidly connected to the cylinder crankcase and its tracer should rest on the crankshaft edge, the pulley or the flywheel. Consequently you should move with some power the crankshaft in its case in axial direction, and you are able to read from the deviations of the dial gauge the axial clearance.How can you - as a driver - take some strain of this bearing? If you drive in a fully automatic gear shift vehicle not much, but if you shift gears yourself you just need to spare the clutch pedal, e.g. by lifting the clutch while you are waiting in front of the traffic lights.
Oil may indicate the clearance
The play of the crankshaft sliding bearings influences the oil pressure. The smaller is the play, the higher the pressure. Therefore, for a long time, the oil pressure was used as an indicator for the play of the crankshaft bearings. 06/07