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What is a torque-to-yield head bolt?

What is a torque-to-yield head bolt? 1What is a torque-to-yield head bolt?
It is a one-time-use fastener that is designed to stretch during installation.
Because of this stretching, the integrity of the bolt is compromised.
These bolts cannot and should not be reused due to the stress caused to the bolt during its first installation.

It is essential to be aware that these bolts will not have the same clamping strength if used a second time.
Torque-to-yield bolts may break if reused or become loose over time.
It is important to note that most repair manuals refer to these bolts simply as one-time-use or single-use instead of torque-to-yield.

How to tighten torque to yield bolts.
Like conventional bolts, torque to yield bolts are also tightened in a specific sequence and number of stages to prevent distortion of the cylinder head. The significant difference is that the initial torque setting is always relatively low.
For example, a typical cylinder head tightening sequence might look like this-

1 – Tighten in stages and sequence to 40Nm
2 – Tighten in sequence to 90degrees
3 – Tighten in sequence a further 90 Degrees

NOTE: The example of a tightening procedure above is just that, an example that is intended for illustrative purposes.
Always refer to the manufacturer’s procedures and specifications when installing bolts to avoid issues later.
Do not assume that your mechanic understands what torque-to-yield bolts are