What is a torque to yield head bolt?

A torque to yield fastener (TTY) or stretch bolt is a fastener which is torqued beyond the state of elasticity and therefore undergoes plastic deformation, causing it to become permanently elongated.

Are all head bolts torque to yield?

They provide more consistent clamping loads, across the entire head-to-block mating surface. When a shop manual indicates that a bolt is to be discarded and new ones used; they are almost always torque to yield bolts.

Are cylinder head bolts torque to yield?

Torque-To-Yield Cylinder Head Bolt. Installation & Removal Tips. Torque-to-Yield (TTY) head bolts are used on many late model engines to clamp the cylinder head to the block. They differ from ordinary head bolts in that TTY bolts are designed to stretch slightly when they are tightened down.

Is it safe to reuse torque to yield bolts?

What is a torque-to-yield bolt? It is a one-time-use fastener that is designed to stretch during the torquing process (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.

What is the advantage of torque to yield bolts?

Torque to yield bolts have many advantages over conventional bolts. The specialised method of tightening these bolts allows them to be more efficient at clamping. Engine reliability is achieved because the assembly of the engine is far more accurate.

Why do you have to replace torque to yield bolts?

If removed and reused, it is likely that either the head gasket will fail (due to low clamp load) or the bolts will break. You should always replace the T-T-Y bolts; these bolts are designed to stretch, and reusing them will cause improper, uneven torque and clamping force.

How many times can torque to yield bolts be used?

Torque to Yield (TTY) fasteners are used in many modern engines. When torqued properly, they provide better clamping force than standard fasteners. All TTY bolts are 1-time use only. However, some rod bolts and main cap bolts can be tightened up to 3 times for assembly purposes.

Is it bad to reuse torque to yield bolts?

Torque-to-yield (TTY) head bolts are designed to stretch when used. Once stretched, they are not as strong as before. Because the tightening procedure permanently stretches the bolts, there is a risk of breakage if reused.

Can you reuse bolts that have been torqued?

When the time comes to dismantle or reassemble, the question of whether or not to reuse nuts and bolts tends to come up. It is possible to reuse fasteners in some cases. However, only fasteners that have never been torqued beyond their yield strength may be used again.

What happens if you reuse head bolts?

A head bolt should not be reused if the threads are galled or badly damaged. Chasing damaged head bolt threads with a die will clean up the threads but also remove material (metal) and undermine the head bolt’s ability to torque down and hold to specs.

Why do head bolts stretch?

Stretch bolts for cylinder heads The clamping force of stretch bolts is necessary to retain the inevitable variations of cylinder head composite gasket material deformations due to heat etc. and they automatically keep the necessary clamping force on the head gaskets for them not to not leak.

Do you reuse torque to Yield ( TTY ) head bolts?

For regular head bolts, make sure all of the head bolts are in good condition; free from nicks, corrosion and are not stretched. Never, reuse torque to yield (TTY) head bolts. Because, if you do, it’s not unusual for them to break.

Can you use more than one torque to yield fastener?

On applications with more than one fastener, such as wheel nuts or cylinder head bolts, the fasteners should be tightened to specification by alternating between the fasteners to ensure the parts are not distorted and that the fasteners are torqued evenly.

How much torque do you need for head bolts?

On the first pass, the head bolts are torqued to 36 foot-pounds. This is the point of elastic deformation. The second pass would be a 90-degree angle or a quarter turn. At this point, the bolt is going into plastic deformation.

Is it possible to reuse a head bolt?

If a head bolt has NOT been subjected to excessive torque; it is most likely reusable a second or even a third time. Determining which bolts have been stretched requires, no special tools other than sharp eyes.