Torque to yield bolts-What are they ?
So, Torque-to-yield TTY bolts are exactly what they sound like.
When tightened they stretch to the point of yield.
Common torque to yield TTY bolts are being used to hold:
- Cylinder heads
- Connecting rods
- Crankshaft main bearing caps
- Front engine dampers
When a shop manual indicates that a bolt is to be discarded and new ones used, they are almost always torque to yield bolts.
Buying new TTY bolts may seem expensive. After all, the old bolts still look good, but looks can be deceiving. Reusing the old bolts can cause expensive engine failure. Hence only new bolts can provide the even clamping force needed on today’s engines.
Why do we need these torque to yield bolts now? We didn’t need them in the 1960′s or 70′s! The simple answer is engine materials are different. Aluminum cylinder heads expand at a different rate than cast iron blocks.