Crankshaft Bearings Figures 12-61 through 12-63 Cleaning and Inspection Clean • Crankshaft with solvent. - Do not scratch the bearing journals. - Remove all sludge from the oil passages with compressed air. • Crankshaft bearing. - Wipe free of oil with a soft cloth. Inspect • Crankshaft for cracks. - Use the magnaflux method if available. - Crankshaft, crankshaft bearing journals, and thrust surfaces for scoring, nicks or damage caused by lack of lubrication. - Main bearing inserts for scoring or other damage. In general, the lower crankshaft bearings (except the #1 bearing) show the greatest wear and distress from fatigue.
Upon inspection, if a lower crankshaft bearing is suitable for reuse, it can be assumed that the upper crankshaft bearing is also satisfactory. If a lower bearing shows evidence of wear or damage, both the upper and lower crankshaft bearings must be replaced. Measuring Bearing Clearance Crankshaft bearings are of the precision insert type and do not use shims for adjustment. If clearances are excessive, new upper and lower bearings will be required. Service bearings are available in standard size and undersize. Selective fitting of crankshaft bearings is necessary in production to obtain close tolerances.
For example, you may find one-half of a standard crankshaft bearing with one-half of an undersize crankshaft bearing. To determine the correct replacement bearing size, the bearing clearance must be measured accurately. Either of the following two methods may be used, however, the micrometer method gives more reliable results and is preferred. Micrometer Method Measure 1 . The crankshaft journal diameter with a micrometer in several places, approximately 90° apart. Average the measurements. 2 . Compute taper and runout. Refer to “Specifi- cations” for allowable limits. Install or Connect 3 . Crankshaft bearings into the crankshaft cap and engine block. 4 . Install crankshaft caps and bolts.
5. Tighten bolts to specification. Measure 6 . Bearing inside diameter (I.D.) using an inside micrometer. 7 . Compare crankshaft bearing clearance with “Specifications”. 8 . If bearing clearances exceed specification, install new crankshaft bearings. A . Measure inside diameter with an inside micrometer at 90° to the split line of the crankshaft bearing. B . Subtract journal diameter from bearing inside diameter to obtain bearing clearance. Refer to “Specifications” for bearing inside clearance. Replace or repair the crankshaft if clearance exceeds specification. Figure 12-61 Measuring Crankshaft Journals G643 (E) Service Manual Chapter 3. Engine Mechanical System 91