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What causes a fastener to lock?

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I am rebuilding a car engine. With some of the fasteners I am unscrewing, I notice that a lot of torque is required to undo the fastener. It feels like a snap when undoing a fastener, rather than a smooth twist. If I tighten the fastener to a set torque again and loosen it, it requires the same torque as it took to fasten it.

Why would this be? My guess would be something to do with heat cycling.

Note: There is no threadlocker on these bolts.

bolting fasteners

share|improve this question

asked 9 hours ago

tgun926tgun926

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2

1

$begingroup$

I am rebuilding a car engine. With some of the fasteners I am unscrewing, I notice that a lot of torque is required to undo the fastener. It feels like a snap when undoing a fastener, rather than a smooth twist. If I tighten the fastener to a set torque again and loosen it, it requires the same torque as it took to fasten it.

Why would this be? My guess would be something to do with heat cycling.

Note: There is no threadlocker on these bolts.

bolting fasteners

share|improve this question

asked 9 hours ago

tgun926tgun926

11111 bronze badge

New contributor

tgun926 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

add a comment | 

$begingroup$

I am rebuilding a car engine. With some of the fasteners I am unscrewing, I notice that a lot of torque is required to undo the fastener. It feels like a snap when undoing a fastener, rather than a smooth twist. If I tighten the fastener to a set torque again and loosen it, it requires the same torque as it took to fasten it.

Why would this be? My guess would be something to do with heat cycling.

Note: There is no threadlocker on these bolts.

bolting fasteners

share|improve this question

asked 9 hours ago

tgun926tgun926

11111 bronze badge

New contributor

tgun926 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

share|improve this question

asked 9 hours ago

tgun926tgun926

11111 bronze badge

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tgun926 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

asked 9 hours ago

tgun926tgun926

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Check out our Code of Conduct.

asked 9 hours ago

tgun926tgun926

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asked 9 hours ago

tgun926tgun926

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3 Answers
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Oxidation, dried lubricant, contaminants, rust - all that acts as a layer of glue binding the elements. As you apply a firm torque, you snap that bond. It takes a considerable time to re-form.

share|improve this answer

answered 9 hours ago

SF.SF.

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Under high pressure and high heat metal bonds by a process called diffusion. Where the atoms of the two parts intersperse over time.

This and oxidation, slow chemical burning of unintentional matrial and debris between the two parts, cause a strong bond that many times cuase the fastener to break before it can be removed.

share|improve this answer

answered 8 hours ago

kamrankamran

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add a comment | 

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$begingroup$

A standard bolt will stretch when tightened. This stretching increases force on the threads of both the bolt and hole and thus increases the force required to overcome static friction and loosen the bolt. If we exclude other materials and chemical changes to the surfaces then that snap that you experience is the moment you overcome that static friction between the two parts.

share|improve this answer

answered 4 hours ago

UseitorLoseitUseitorLoseit

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4

$begingroup$

Oxidation, dried lubricant, contaminants, rust - all that acts as a layer of glue binding the elements. As you apply a firm torque, you snap that bond. It takes a considerable time to re-form.

share|improve this answer

answered 9 hours ago

SF.SF.

4,7951313 silver badges4141 bronze badges

$endgroup$

add a comment | 

4

$begingroup$

Oxidation, dried lubricant, contaminants, rust - all that acts as a layer of glue binding the elements. As you apply a firm torque, you snap that bond. It takes a considerable time to re-form.

share|improve this answer

answered 9 hours ago

SF.SF.

4,7951313 silver badges4141 bronze badges

$endgroup$

add a comment | 

$begingroup$

Oxidation, dried lubricant, contaminants, rust - all that acts as a layer of glue binding the elements. As you apply a firm torque, you snap that bond. It takes a considerable time to re-form.

share|improve this answer

answered 9 hours ago

SF.SF.

4,7951313 silver badges4141 bronze badges

$endgroup$

share|improve this answer

answered 9 hours ago

SF.SF.

4,7951313 silver badges4141 bronze badges

answered 9 hours ago

SF.SF.

4,7951313 silver badges4141 bronze badges

answered 9 hours ago

SF.SF.

4,7951313 silver badges4141 bronze badges

2

$begingroup$

Under high pressure and high heat metal bonds by a process called diffusion. Where the atoms of the two parts intersperse over time.

This and oxidation, slow chemical burning of unintentional matrial and debris between the two parts, cause a strong bond that many times cuase the fastener to break before it can be removed.

share|improve this answer

answered 8 hours ago

kamrankamran

5,78422 gold badges55 silver badges1313 bronze badges

$endgroup$

add a comment | 

2

$begingroup$

Under high pressure and high heat metal bonds by a process called diffusion. Where the atoms of the two parts intersperse over time.

This and oxidation, slow chemical burning of unintentional matrial and debris between the two parts, cause a strong bond that many times cuase the fastener to break before it can be removed.

share|improve this answer

answered 8 hours ago

kamrankamran

5,78422 gold badges55 silver badges1313 bronze badges

$endgroup$

add a comment | 

$begingroup$

Under high pressure and high heat metal bonds by a process called diffusion. Where the atoms of the two parts intersperse over time.

This and oxidation, slow chemical burning of unintentional matrial and debris between the two parts, cause a strong bond that many times cuase the fastener to break before it can be removed.

share|improve this answer

answered 8 hours ago

kamrankamran

5,78422 gold badges55 silver badges1313 bronze badges

$endgroup$

share|improve this answer

answered 8 hours ago

kamrankamran

5,78422 gold badges55 silver badges1313 bronze badges

answered 8 hours ago

kamrankamran

5,78422 gold badges55 silver badges1313 bronze badges

answered 8 hours ago

kamrankamran

5,78422 gold badges55 silver badges1313 bronze badges

1

$begingroup$

A standard bolt will stretch when tightened. This stretching increases force on the threads of both the bolt and hole and thus increases the force required to overcome static friction and loosen the bolt. If we exclude other materials and chemical changes to the surfaces then that snap that you experience is the moment you overcome that static friction between the two parts.

share|improve this answer

answered 4 hours ago

UseitorLoseitUseitorLoseit

1133 bronze badges

New contributor

UseitorLoseit is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

add a comment | 

1

$begingroup$

A standard bolt will stretch when tightened. This stretching increases force on the threads of both the bolt and hole and thus increases the force required to overcome static friction and loosen the bolt. If we exclude other materials and chemical changes to the surfaces then that snap that you experience is the moment you overcome that static friction between the two parts.

share|improve this answer

answered 4 hours ago

UseitorLoseitUseitorLoseit

1133 bronze badges

New contributor

UseitorLoseit is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

add a comment | 

$begingroup$

A standard bolt will stretch when tightened. This stretching increases force on the threads of both the bolt and hole and thus increases the force required to overcome static friction and loosen the bolt. If we exclude other materials and chemical changes to the surfaces then that snap that you experience is the moment you overcome that static friction between the two parts.

share|improve this answer

answered 4 hours ago

UseitorLoseitUseitorLoseit

1133 bronze badges

New contributor

UseitorLoseit is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

share|improve this answer

answered 4 hours ago

UseitorLoseitUseitorLoseit

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answered 4 hours ago

UseitorLoseitUseitorLoseit

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answered 4 hours ago

UseitorLoseitUseitorLoseit

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