Installation of engine bearings
Step by step instructions
When installing engine bearings, instructions should be followed precisely. Checking the dimensions and tolerances is after all particularly important for mounting. We provide an overview of which clearances and tolerances should be noted.
Diameter and roundness measurements on straight or inclined split connecting rodsThe tightening specification must be observed for every machining and measurement process. As the diagram shows, two measurements are necessary:
- Measurement on the installation bore (without bearing shell).
Note: Observed manufacturer's instructions if conrods have cracked!
- Measurement with bearing shells inserted
For the bore dimensions, the tolerances stated in the catalogue apply.
Permitted taper and roundness:
|up to 25 mm
|max. 3 µm
|max. 3 µm
|25 to 50 mm
|max. 5 µm
|max. 5 µm
|50 to 120 mm
|max. 7 µm
|max. 7 µm
Permitted deviations: Overall concentricity of all bearing counter bores max. 0.02 mm Concentricity between adjacent bearing counter bores max. 0.01 mm
During crankshaft reconditioning, inspections for cracks must be carried out after aligning, after hardening and after grinding.
Final inspection of crankshaft
Maximum values for tapered, convex or concave ground shafts:
|up to 30 mm
|over 30 to 50 mm
|over 50 mm
Check for radial eccentricity
Permitted misalignment of main bearing journal:
Adjacent journal: 0.005 mm
Total: 0.01 mm
These tolerances are standard values unless different figures are specified by the manufacturer.
Compliance with surface quality and dimensional tolerance specifications is particularly important with radius hardened bearing journals.
Measuring the radiusIf the correct radius gauge is selected, there should be no visible gap.
Crankshaft hardness test
Are the bolts OK?
Bolts with visible mechanical damage must be replaced. Bolts tightened by torque and angle permanently lengthen and can therefore no longer be used.
Selecting the right plain bearings
“KS Plastic Gauge” measuring strip
“KS Plastic Gauge” is a thin, calibrated plastic strip, which is inserted in the oilfree bearing point to measure the bearing clearance. When the bearing cap is tightened, the strip is squashed widthways.
After the bearing cap has been released and removed, the resulting width of the plastic strip is measured and the bearing clearance determined using the supplied reference scale. The bearing clearance can be read in mm and in inches.
Measuring range: 0.025 to 0.175 mm
Scope of delivery: 10 measuring strips, measuring instructions and measuring scale
Oil on the shells. Use an oil can. A brush may transfer dirt particles from the oil container.
Correct axial clearanceThe flanged bearing is designed with extra width for repair purposes. If you grind the crankshaft to match this bearing shell width or thrust washer thickness, you will adhere to the correct axial clearance. Information on engine-specific axial clearance can be obtained from the engine manufacturer.
Some repair grades of flanged bearings and thrust washers are designed with additional width allowance.
This process is generally prescribed by many well-known engine manufacturers before starting a new or overhauled engine for the first time.