Inspecting the crankshaft plain bearings
- To obtain a good bushing lubrication it is neces-
sary to have both an optimal lubricating pressure
(4 bar) and a good oil flow rate; the bushings must
be correctly positioned so as not to obstruct the oil
supply channels.
- The main bushings are comprised of two half-
bearings, one with holes and channels for lubrica-
tion whereas the other is solid.
- The solid half-bearing is intended to stand the thrusts caused by combustion, and for this reason it is
arranged opposite the cylinder.
- To prevent obstructions in the oil feeding channels, the matching surface of the two half-bearings must
be perfectly perpendicular to the cylinder axis, as shown in the figure.
- The oil feeding channel section is also affected by the bushings driving depth compared with the
crankshaft axial clearance of the limiting surface.
N.B.
TO KEEP THE BUSHINGS ON THE CRANKCASE IN SUCH POSITION, DRIVING IS FORCED ON
CAST-IRON RINGS INSERTED IN THE CASTING OF BOTH CRANKCASE HALVES.
- Check the inside diameter of the main bushings
in the three directions indicated in the diagram.
- Repeat the measurements for the other bushing
half. see diagram.
N.B.
DO NOT TAKE THE MEASUREMENT ON THE TWO HALF-
SHELL COUPLING SURFACE SINCE THE ENDS ARE RE-
LIEVED TO ALLOW BENDING DURING THE DRIVING
OPERATION.
- The standard bushing diameter after driving is variable on the basis of a coupling selection.
- The bushing seats into the crankcases are classified into 2 categories as for the drive shaft Cat. 1 and
Cat. 2.
- Bushings are divided into 3 categories according to their thickness. See the table below:
CHECK THE BENCH BUSH
Name
Description Dimensions Initials Quantity
Type A - Red 1.982 - 1.987
Type B - Blue 1.987 - 1.992
Type C - Yellow 1.992 - 1.997
Engine Beverly 500 i.e.
ENG - 146
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