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Bolts with turn tightening - necessary to replace every time?

Engine Building Fundamentals

Discussion and questions related to the course Engine Building Fundamentals


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Hello.

Coud you please clarify? In "Bolt Clamping Force" lesson you said that if head bolt is tightened by torque then turn to some angle - they should be replaced after first use. But if we for example we take Toyota 3S-GTE repair manual - it says

1) 49Nm

2) Turn 90 degerees

3) If any cylinder head bolt is broken or deformed, replace it.

So it looks like, even if we use torque-then-turn, bolt is still in elastic region? And can be re-used?

Attached Files

my understanding is you can reuse bolts unless stated by the manufacturer not to reuse them but i could be wrong unless they are stretched passed there elastic limit they should return to original size

but in "Bolt Clamping Force" video Andre said that if we turn for some angle after reaching some tightening torque - it means that we passed yield point. I'm just trying to understand the idea.

The manufacturer of OEM equipment or aftermarket supplier should specify if they are torque to yield or not. It doesn't matter if your final setting is via measurement of stretch, torque or torque & angle, what matters if if they are still in their elastic range or not.

If OEM bolts are still in elastic area - why we should use angle? Why we can't use just increased torque?

So "50 Nm, then 90 degerees" may be just "60Nm" for example? If bolt still in elastic area of the graph?

I treat every fastener with torquing methods like that as a TTY and replace them. If it's a critically important fastener then it's a small price to pay. If it isn't, I value my time and its still a small price.

After surfing the web I've found that torque-then-angle not always means reaching yield point. So it looks like in my first post about Toyota manual - yield point isn't reached and bolts are reusable.

There are two tightening technuques with angle: Torque Turn to Tighten (TTT) and explicitly Torque To Yield (TTY).

Now it's clear.

Ok so to add some clarity, while the majority of fasteners that use a torque-angle are TTY and must be replaced, this isn't always the case. As stated in a reply above, the factory workshop manual will tell you if the fasteners must be replaced. Often there will be an under head measurement that you can use to guide you as to whether the fastener has been stretched or permanently deformed.

Andre, thank you.