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Rear Main Seal Replacement

Contributed By: Joe Schaefer

NOTE: This is from the 1973 Jeep Technical Service Manual J-73-1001 and applies to all 258/304/360 and 401 engines.

The rear main bearing crankshaft seal consists of a two piece neoprene single lip seal to effectively seal the rear of the crankshaft. Correct installation of the seal will insure leak free engine operation (Fig 36).

Removal and Installation

  1. Drain the engine oil and remove the oil pan.
  2. Remove the oil pan front and rear neoprene oil seals.
  3. Remove the oil pan side gaskets.
  4. Thoroughly clean the gasket surfaces of the oil pan and engine block.
  5. Remove all sludge and dirt from the oil pan sump.
  6. Remove the rear main bearing cap.
  7. Remove and discard the lower seal.

    IMPORTANT: To ensure leak free operation, the upper and lower seal halves must be replaced in pairs.

  8. Clean the main bearing cap thoroughly to remove all sealer.
  9. Loosen all remaining main bearing caps.
  10. With a brass drift and hammer, tap the upper seal until sufficient seal is protruding to permit pulling the seal out completely.
  11. Wipe the seal surface of the crankshaft clean; then oil lightly.
  12. Coat the block contacting surface at the upper seal with soap, and the lip of the seal with engine oil.
  13. Install the upper seal into the engine block.

    CAUTION: The lip of the seal must face to the front of the engine.

  14. Coat both sides of the lower seal end tabs with "Permatex" No. 2 or equivalent, being careful not to apply sealer to the lip of the seal.
  15. Coat the outer curved surface of the lower seal with soap and the lip of the seal with engine oil.
  16. Install the seal into the cap recess and seat it firmly.
  17. Place "Permatex" No. 2, or equivalent, on both chamfered edges of the rear main bearing cap.
  18. Install the rear main bearing cap and inserts.
  19. Tighten all main bearing cap screws to the specified torque.
  20. Install oil pan using new gaskets and seals.
  21. Tighten the drain plug securely.
  22. Use new engine oil to fill the crankcase to the specified level.
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