Head bolts provide the clamping force that holds the cylinder head, head gasket and block together. If that clamping force is too low or uneven, even a brand-new head gasket can leak. One of the most common causes is reusing head bolts that were designed to be installed only once.
What Are Torque-to-Yield Bolts?
Many modern engines use torque-to-yield (TTY) head bolts. They are tightened to an initial torque and then turned a specified number of degrees, which stretches the bolt slightly past its elastic range. This produces a very consistent clamping load, but the bolt is permanently stretched afterward.
Why Reuse Is a Risk
- A stretched bolt cannot reliably deliver the same clamping force a second time.
- Used bolts can neck down or break during installation or later in service.
- Uneven clamping load can allow combustion gas, coolant or oil to leak past the head gasket.
Some engines use bolts that the manufacturer allows to be reused after checking their length. Always follow the service information for the specific engine.
Installation Tips
- Clean the bolt holes in the block and remove any oil or coolant. Liquid trapped in a blind hole can prevent the bolt from seating or crack the block.
- Chase the threads if needed, and check that the head and block deck surfaces are clean and flat.
- Lubricate the threads and under the bolt heads only as specified.
- Follow the tightening sequence, torque values and angle steps exactly, using a calibrated torque wrench and an angle gauge.
Evergreen Head Bolt Sets
Evergreen head bolt sets are identified by engine application, and many Evergreen cylinder head gasket sets and rebuild kits can be paired with a matching bolt set. See cylinder heads and components and gasket sets and seals, or use the Evergreen eCatalog.
