ASE A1 Engine RepairCylinder Head and Valve TrainHard
A technician is assembling a cylinder head and is preparing to install the new cylinder head bolts. The service manual specifies 'torque-to-yield' (TTY) bolts and outlines a multi-step tightening procedure involving initial torque values followed by specific angle turns (e.g., 30 Nm, then +90°, then +90°). What is the primary characteristic of TTY bolts that necessitates this specific tightening method?
- AThey are designed to stretch plastically during tightening for optimal clamping force.
- BThey provide a more accurate torque reading than conventional bolts.
- CThey are designed to be reused multiple times without stretching.
- DThey require less torque than conventional bolts for the same clamping force.
Show answer & explanationAnswer & explanation
Correct answer: A. They are designed to stretch plastically during tightening for optimal clamping force.
Torque-to-yield (TTY) bolts are specifically designed to be tightened beyond their elastic limit into their plastic deformation range. This stretching provides a more consistent and higher clamping force, but it also means they cannot be reused.
Why the other options are wrong
- B. TTY bolts are tightened by angle, not just torque, because torque readings become unreliable once the bolt yields. The angle ensures the desired amount of stretch.
- C. TTY bolts are designed to stretch plastically and should never be reused, as they have lost their clamping integrity.
- D. TTY bolts often achieve a very high clamping force, which might require a combination of torque and angle that results in a higher effective clamping force than conventional bolts, not necessarily less torque.
Torque-to-Yield (TTY) Bolts
Cylinder head bolts designed to be tightened beyond their elastic limit into their plastic deformation range, providing optimal and consistent clamping force.
- Stretches plastically during tightening.
- Provides consistent, high clamping force.
- Must be replaced after one use.
- Tightened with a specific torque-plus-angle method.
Memory trick: Yield and stretch, one-time catch.