Using a torque wrench incorrectly or guessing the ft-lbs on a cylinder head is a recipe for a blown head gasket or warped deck. The manual lists:
The 4FG1 is distinct from its smaller sibling (4FB1) by having a larger bore and a specific fuel injection pump (Bosch VE or Zexel). If you are working on this engine without the manual, you are essentially flying blind through a high-pressure diesel maze. Isuzu 4fg1 Engine Manual
Websites like or ManualsLib offer the 4FG1 manual in searchable PDF format for ~$15–$30. The searchable text is critical for finding terms like "injection pump overflow valve." Using a torque wrench incorrectly or guessing the