Understanding Torque-to-Yield
Head Bolts
T-T-Y head bolts are particularly common on engines using
aluminum heads and/or multi-layer steel head gaskets.
These bolts are engineered to stretch within a controlled
“yield zone”. Once they reach this zone, they spring back to
provide a precise level of clamping force over the entire
area of the gasket.
It’s important to carefully follow the manufacturer’s
tightening specication. Once T-T-Y bolts are stretched
beyond their yield zone, they become useless. Typically,
T-T-Y bolts are torqued to a specied limit, then again with
an additional partial turn to reach the bolt’s yield zone.
It is recommend to never reuse a T-T-Y head bolt. Chances
are too great that it has already exceeded its elasticity barrier
and won’t spring back to properly seal the engine.
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