Torque Tables

 Torque Tables

Complete Cylinder Head Torque Specifications for Domestic and Imported Passenger Cars and Light/ Medium Duty Trucks

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 specification. Once T-T-Y bolts are stretched beyond their yield zone, they become useless. Typically, T-T-Y bolts are torqued to a specified 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.

Importance of Proper Torque

When a head gasket is installed between the cylinder head and engine block, tightening the head bolts compresses the gasket slightly, allowing the soft facing material on the gasket to conform to the small irregularities on the head and block deck surfaces. This allows the gasket to “cold seal” so it

won’t leak coolant before the engine is started. The head gasket’s ability to achieve a positive cold seal, as well as to maintain a long-lasting, leak-free seal depends on two things: its own ability to retain torque over time (which depends on the design of the gasket and the materials used in its construction) and the clamping force applied by the head bolts.

PermaTorque® head gaskets are made with top-quality materials and designed to remain resilient so they retain torque, so no retorquing is necessary. (Some competitive head gaskets alleged to be “no retorque” can lose as much as 50 to 60% of their original torque after only 100 hours of service.)