Crankshaft Main Bearing Service

Some production crankshafts are ground to .009" (.23 mm) undersize at the assembly plant. They are identified as follows:

• Crankshaft counterweight of undersize journal, will be stamped on one side with the number "9," along with a large spot of light green paint.
• Main bearing cap will be painted light green on each side.
  1. Mark or identify main bearing cap before removing. Support crankshaft weight, using a jack placed under counterweight next to the bearing being checked. Loosen drive belts from crankshaft pulley, prior to checking No. 1 bearing.
  2. Remove main bearing cap and place a piece of Plastigage across full width of bearing, about 1/4" off center, and away from oil holes. Install cap and tighten to specifications. Do not allow crankshaft to turn.
  3. Remove cap and measure width of Plastigage with scale furnished. Standard, .001" (.03 mm) or .002" (.05 mm) undersize bearing halves may be used in combination to obtain correct clearance. Always replace both upper and lower bearing halves.
  4. With the exception of rear main bearing, main bearings are removed from cylinder block using remover/installer tool (J-8080 or equivalent). Insert tool in crankshaft oil hole and rotate crankshaft clockwise. If tool not available, a cotter pin may be bent, as necessary, to do the job.
  5. To remove rear main bearing from block, partially drive out bearing with a drift. Use a pair of pliers (with jaws taped) to hold bearing thrust surface to the oil slinger, and rotate crankshaft to remove bearing.
  6. Lubricate journal and bearings. Insert plain end of new bearing between crankshaft and notched side of block. Insert bearing remover/installer tool into crankshaft oil hole, and rotate bearing into place. To install rear main bearing, use pliers (as used in removal), to aid in installation.
  7. Install lower bearing half into cap. Install and tighten main bearing caps with arrows pointing toward front of engine. Align thrust bearing, then check crankshaft end play. Check end play by prying crankshaft forward, and inserting feeler gauge between crankshaft counterweight and forward face of rear main bearing cap.