Plastigage Method Install or Connect 1 . Main bearing inserts and crankshaft. 2 . Gauging plastic. A . Begin with the rear main bearing. B . Wipe the oil from the crankshaft journal and the lower main bearing insert. C . Place a piece of gauging plastic the full width of the lower bearing insert (parallel to the crankshaft) on the journal (figure 12-62). Do not rotate the crankshaft while the gauging plastic is between the bearing and journal. 3 . Main bearing cap and bolts. 4 . Tighten bolts to specification. Remove or Disconnect • Main bearing cap. DO NOT REMOVE THE GAUGING PLASTIC FROM THE JOURNAL OR LOWER MAIN BEARING INSERT. Figure 12-63 Measuring Gauging Plastic c.
If the flattened plastic tapers toward the middle or ends, there is a difference in clearance indicating taper, low spot, or other irregularity of the bearing or journal. d. Normally, crankshaft bearing journals wear evenly and are not out-of-round. However, if a bearing is being fitted to an out-of-round 0.0254 mm (0.001 in.) (maximum) journal, be sure to fit to the maximum diameter of the journal. If the bearing is fitted to the minimum diameter and the journal is excessively out-of- round, interference between the bearing and the journal will result in rapid bearing failure. e. If the bearing clearance is within specifications, the bearing is satisfactory.
If the clearance is not within specifications, replace the bearing. Always replace both upper and lower bearings as a unit. f. A standard or undersize bearing combination may result in the proper clearance. If the proper bearing clearance cannot be achieved using standard or undersize bearings, it will be necessary to replace the crankshaft. NOTICE: Crankshaft bearings must not be shimmed, scraped, or filed. Do not touch the bearing surface with bare fingers. Skin oil will etch the bearing surface. g. Remove the flattened gauging plastic. h. Measure remaining journals. Figure 12-62 Placing Gauging Plastic on Journal Measure • Gauging plastic as follows: a .
The flattened gauging plastic will be found adhering to either the lower bearing insert or journal. b . On the edge of the gauging plastic envelope there is a graduated scale. Without removing the gauging plastic, measure its compressed width (at the widest point) with the graduations on the gauging plastic envelope (figure 12-63). G643 (E) Service Manual Chapter 3. Engine Mechanical System 92