The bearings have locating tangs that fit into notches in the connecting rod and cap. Make sure that the tangs enter the notches correctly. See the comments about bearing spread and crush that follow.
Bearing clearance cannot be adjusted. Any attempt to correct bearing clearance by filing the connecting-rod cap will destroy the original relationship between the cap and the rod. This will cause early bearing failure.
Crush is caused because the edge of the bearing insert stands above the parting face of the connecting rod or cap. This additional height is ‘crushed’ when the cap is installed and the bolts tightened. Crushing pushes the inserts into the bore in the connecting rod and cap. This ensures that the backs of the inserts are in snug contact with the bore. Figure 7.22 shows
Crush is a general term as described, but it can also refer to the distance that the edge of the bearing stands above the parting face.
The clearance of a connecting-rod bearing can be found by using a telescopic gauge to measure the bearing and a micrometer to measure the journal. However, the easiest way is with Plastigage.
When used to check the clearance of a connecting- rod bearing, a strip of the material is placed in the bearing in the cap. The cap is installed and the nuts are tightened to the correct torque. The bearing cap is then removed and the flattened Plastigage is measured (Figure 7.23). If the Plastigage is flattened only a little, then there is a large-clearance, and vice versa.
A printed scale is supplied with the Plastigage. The scale has bands of different widths which are marked to show the bearing clearance — for example, 0.02 mm, 0.03 mm etc. The scale is placed against the flattened Plastigage to check its width as shown in the illustration.
3. Place a small strip of Plastigage in the centre of the bearing and install the bearing cap on the connecting rod.
4. Remove the bearing cap and check the thickness of the flattened Plastigage against the scale.
The heavy-pressure spots C and D on the piston will cause heavy wear and possibly scoring of the piston and cylinder wall. A basic inspection check is to look for uneven wear or shiny spots on the pistons, which will indicate misalignment. If this condition is found, the connecting rod should be checked and as necessary, straightened or replaced.