How do torque to yield bolts work?

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.

What is a torque-to-yield bolt?

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.

How do you tighten torque-to-yield bolts?

How to tighten torque to yield bolts

  1. Tighten all bolts in sequence, and in two stages to a snug torque value of say, 30 Nm.
  2. Apply a 90 degree rotation to all bolts in the proper tightening sequence.
  3. Apply a further 90 degree rotation to all bolts in the proper tightening sequence.

Are torque yield bolts better?

Torque to Yield (TTY) fasteners are used in many modern engines. When torqued properly, they provide better clamping force than standard fasteners. … When swapping heads or rebuilding an engine, always replace any TTY bolts with new ones.

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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.

What happens if you over torque a torque to yield bolt?

If the bolt is over-torqued and stretched beyond its limit, this exceeds its yield strength which means it can no longer maintain the needed clamp load and must be replaced. … Finally, using a breaker bar, the bolt is tightened, which moves the dial to the specified angle – hence the term torque-angle.

Why do manufacturers use torque to yield bolts?

Many vehicle manufacturers use torque to yield bolts; especially on engines with aluminum heads and or in conjunction with (MLS) head gaskets. Because, they provide more consistent clamping loads, across the entire head-to-block mating surface. … Reusing the old bolts, can cause expensive engine failure.

How many times can torque to yield bolts be used?

* Never reuse a torque-to-yield bolt. Because the bolts are designed to stretch once, stretching them a second time may stretch them beyond their yield point causing the bolt to break. They are one-time use bolts, so throw the old bolts away and buy new ones.

What is yield point torque?

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.

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Should bolts be lubricated before torquing?

So, torque isn’t the true measure of bolt tightness—it’s tension. But lubrication on the bolt threads—and a whole host of other factors—can cause fluctuation in torque readings. So once you add a lubricant of any kind to the threads, all bets are off as to whether the same torque setting will truly secure the bolt.

Can stretch bolts be reused?

stretch to ensure proper securing when tightened down. (Bolts with Specification: Torque plus Angle). Some of these bolts can be reused, if you torque them to the same torque that you would use for a normal bolt of the same size, pitch, lubrication factor, and strength rating.

Can you reuse head bolts?

Can I 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.

What happens when you over tighten bolts?

Everyone who has ever worked with fasteners has accidentally messed one up at some point. One of the most damaging ways to do that is by over-tightening, or over torquing the fastener. This can result in stripping screws, snapping screw heads and damaging pre-tapped threading.

Can you reuse head bolts on a 5.7 Hemi?

No. You should never reuse TTY(torque to yield) bolts or most head bolts at all.

What is torque to spec?

Recommended torque specifications are unique for each type of vehicle. … By definition, torque refers to the amount of rotational force at the point of application. When attaching a wheel to a vehicle, torque specifications are the amount of force recommended on the hardware to ensure proper installation.

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