After fitting a new head gasket, re-torque after the very first warm-up and complete cool down -- I wait until the next day. Consult the manual as to whether further re-torques are necessary.
Re-torque:
- mark each bolt head for position -- I use a sharpie and mark a line parallel to the engine.
- follow the torque pattern.
- loosen the first bolt a half-turn using a breaker bar.*
- fit the torque wrench and turn to specified torque setting.
- it must at least go back to where it was, preferably further.
- move to the next bolt in the order and repeat.
Engines driven very hard will require re-torqueing even if it is not specified in the manual. Not sure? Mark and check the first bolt in the sequence. Moves further than marked? Do the rest as well.
* never, ever use a torque wrench to loosen a fastener. Yes, I know some have a switchable ratchet, or a fixed beam, but don't do it regardless. It may throw your wrench out of calibration. Speaking of which, when was the last time you had your wrench calibrated?
