Q: What is a TTY bolt?
A: Torque to Yield (TTY) fasteners are used in many modern engines. When torqued properly, they provide better clamping force than standard fasteners.
All TTY bolts are designed for one-time use only. However, some rod bolts and main cap bolts can be tightened up to three times for assembly purposes. (Check your service manual for specific details.)
NOTE: When swapping heads or rebuilding an engine, always replace any TTY bolts with new ones.
Overview of Torque to Yield (TTY) Fasteners
Why can’t they be reused?
TTY fasteners have an elastic quality. They are designed to stretch to a specific “yield zone.”
When the fastener is torqued properly, it acts like a spring to apply consistent clamping force. However, the stretch is permanent. After they are torqued, they will never go back to the way they were.
How are they identified?
If a bolt is TTY, the final torque spec will list an angle in degrees rather than foot-pounds (ft.-lbs.).
Which engines use them?
TTY fasteners are used on most modern engines, like:
- Chevy LS and LT engines
- Ford Modular V8
- Chrysler Gen. 3 Hemi
Do they require special tools?
Can I replace them with a reusable bolt?
TTY fasteners should only be replaced with high-quality ARP bolts or studs.
For a deeper dive on TTY bolts, check out Ask Away! with Jeff Smith: The The Truth Behind Torque-to-Yield Fasteners and Torque Angle Fastening.