* Head gasket failure: The most common reason for retorquing head bolts is suspicion of a head gasket leak. Retorquing *might* temporarily address a very minor leak, but it's often a sign of a more serious problem that needs proper diagnosis and repair. Simply retorquing won't fix a blown head gasket or warped head.
* Stretching: Head bolts are designed to stretch slightly during the initial tightening process. This stretching provides the clamping force needed to seal the head gasket. Retorquing them after they've already stretched can further damage them, making them weaker and more likely to fail.
* Material fatigue: Over time, the bolts can experience material fatigue, weakening them even if they haven't been significantly over-torqued. Re-torquing exacerbates this.
* Incorrect torque: Unless you have a torque wrench and know the precise torque specification for your engine (found in your service manual), you risk over-torquing or under-torquing, both of which can cause significant damage.
When re-torquing *might* be considered (with extreme caution):
* Post-engine rebuild: Some engine rebuild procedures specify retorquing head bolts after a certain break-in period. This is done to ensure consistent clamping force after the head gasket has settled. However, this is a very specific situation and should *only* be done following the exact instructions in the rebuild manual.
* Engine overhaul: If you've completely overhauled the engine and replaced the head gasket, retorquing might be part of the procedure, again, only according to the specific instructions.
Instead of retorquing, if you suspect a problem:
* Diagnose the issue: Determine the cause of the leak or problem before taking any action. A compression test, leak-down test, or coolant pressure test can help pinpoint the problem.
* Consult a professional: A qualified mechanic can properly diagnose the issue and determine the appropriate repair method, which might include replacing the head gasket, head bolts, or even the cylinder head itself.
In short, re-torquing old head bolts is generally a bad idea. It's a temporary fix at best and could lead to serious engine damage. Proper diagnosis and repair are always the best approach.
