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Discussion Starter · #1 · (Edited)
And your bolts for that matter!

How well do you know your nuts and bolts?
What do those markings mean on the head of the bolt?
What exactly is torque anyway?
How does locktight or oil affect torque?

Well the questions can go on and on, so I wanted to do a write up to answer those questions above and a few more. Once you have a better understanding of your nuts and bolts and some nitty gritty behind the science of them, you will have a better appreciation of how this applies to you and your car. Note: I am keeping this post very simplified because this subject can easily get very in-depth and boring quite quickly.




Boltology and Nutology 101

I wanted to first start out by briefly getting into why a bolt or nut says in place. Bolts and nuts do not merely stay in place just because they are tight. There is a whole lot of physics and science behind this with a lot of Greek letters and algebraic variables, and if you are into this sort of thing (which I'm not), the information can be easily found with simple searches, As I stated, I am not into all that and as such, I do not want to introduce that bore here, besides I was never that good at that kind of math anyway.

So quite simply, bolts stretch when torque is applied. Like a spring or rubber band that is stretched, the natural tenancy of a bolt is to retract back to it's normal (static) condition.

When components are bolted together with this tenancy to retract, this creates a condition known as the "clamping force". It's this clamping force (and friction) that keeps a bolt or nut in place.

If a bolt or nut is torqued too much, the bolt will stretch more than it was designed to and will not be able to retract back thus lessening the clamping force that is specified for that bolt.

If a bolt or nut is not torqued enough, then again the clamping force will not be achieved, and the bolt can loosen itself.

This is why having a good quality torque wrench is vitally important. Notice I said good quality, but I will get into that later. By not using a torque wrench to tighten your nuts and bolts, you are setting yourself up for eminent failure of that nut or bolt.

Here is a very good 10 minute video explaining torque if you are so inclined to watch.

https://www.youtube.com/watch?v=3E42q4hYJ8I

The top reasons bolts and nuts fail are
Overloading
Overtorquing
Undertorquing
Corrosion


Bolt Styles and Types

As a DIYer, you will encounter several different types of bolts/screws. Below is a chart of the nomenclature of what you might see.



I have not seen any Slotted or Square drive type bolts/screws on the E46, however the Torx is quite
common
.


Bolt and Nut Grades
Have you ever noticed that bolt heads have lines or numbers on them and wondered what the heckfire do those mean? Well my friend, you have come to the right place to get some education. Nuts and bolts are graded on the material that they are made of. The larger the grade the stronger the bolt/nut. US bolts or SAE have a different grade rating system than their metric, or ISO, counter parts, however the same holds true for metric, the larger the grade the stronger the bolt/nut. Also, the higher the grade, the higher the torque that can be applied.


Here is a chart of the most common Metric bolt markings.



Here is a chart of the most common SAE bolt markings.


There are more grades than what are shown in the pictures above, these are just some common ones. You may see letters also stamped into the heads. These letters have different meanings, typically indicating a manufacture. One exception to the letters is "TTY" You may come across this as you do your own work on your car. TTY will be a topic of discussion a bit later.

Note: Metric 8.8 is equivalent to SAE 5, Metric 9.8=SAE 7 and Metric 10.9=SAE 8

Nuts too have markings to indicate their craft material and strength levels, however Identifying nuts is not as easy or straight forward as bolts are. As with bolts, the higher the grade the stronger the nut.







Time to talk TTY, no it's not the teletypewriter! It's Torque To Yield

Ok, many of you's here have no clue as to what this is, some of you do, but do not care, and others are quite knowledgeable about TTY Bolts.

This is a critical subject, so pay attention boys and girls!

There are a few places on your E46 that have TTY bolts, such as the reinforcement plate, Control Arm and suspension components, Engine block /head just to name a few.

Basically these type of bolts are used in areas of high frequency high load situations that have a higher risk of fatigue related failure.

If you are using the Bently manual :read: for instruction for the task you have at hand, you will know a bolt is a TTY bolt when the manual plainly states. "Replace Bolt" even though this statement seems unambiguous, you would be wise to heed it's simple warning.

The reason these bolts need to be replaced after a single usage is that they are engineered to stretch within a controlled yield zone. Once they reach this zone, they are designed to spring back to provide a more precise level of clamping force. This stretch approaches the bolts' elastic limit which permanently stretches it, therefore they cannot be used again.

Did you catch that?! They CANNOT be used again.

As mentioned before, TTY bolts are used on the reinforcement plate, there are 8 of these bolts for you non Xi types. The reinforcement plate is a part that is frequently taken off to work on the underside of the car.



I would venture to say :eek: that most home mechanics like the one that you are, do not replace these bolts, you just reuse the old ones. This is a common noob mistake. Each time these bolts are reused, they become more weakened than the time before, and because this reinforcement plate is a critical component to your cars frame and suspension, you are just inviting trouble to dinner. Do yourself a flavor, and buy extra of these bolts and just keep them on the shelf for future work. I know it sucks to get the plate off and not have replacement bolts on hand, maybe you didn't think ahead, or the job was last minute. In either case, it just means you're going to put the old ones back on, because you do not want to, or cannot wait for new ones to come in the mail, or you can't get to the dealer to pick them up.
Here, Ill help you out, here is a link to these bolts. (Verify proper fitment to your car first however).
The 30 bucks or so is very little to ask as compared to a repair job for a screwed up front end of your car, that's if it is even fixable.







To add or not to add....lubricant/threadlocker

Lubricant

You may read in places that oil is added to bolts and nuts, like studs on engine block for example. If you pull up torque charts for various bolts, you will likely see two values, a wet one and a dry one. Dry values will have a higher torque numbers. The reason being, oil will change the amount of torque needed to stretch a bolt by reducing the friction over that of a dry one. The oil gives a more even torque around the entire thread of a bolt. So why not just put oil on all you bolts then? Most bolts that the normal DIYer will be dealing with have a larger safety zone between the safe torque (aka, proof load) and the overtorque range (aka yield strength). Bolts that have a smaller zone between proof load and yield strength are the types of bolts that oil benefits. This is common in spacecraft/aircraft. Simply put, lubrication allows the bolt to be placed closer to it's yield strength. This just is not necessary in most cases for the E46




Threadlocker

Commonly known as Loctite. Loctite is a chemical thread locking compound. In addition to thread locking, it also has corrosion inhibitors, reduces friction, provides 100% contact between the metal parts, and reduces galling. When you use a threadlocker, it is reported that you use the dry torque values, not the wet as we talked about above. There are several different types of Loctite that you need to know about. You do not want to use the wrong type for your application.


Note: Never use red unless you have to for a specific reason to do so

This chart depicts the "Loctite" brand and their system, however, knockoff threadlockers usually use the same numbering system as Loctite. Red is sometimes referred to be permanent because of it's strength properties. And it has been reported that heads of bolts treated with a red loctite have snapped off because the hold is so strong. However if the bolt is heated up to the Loctite temp range, the bolt will release.





Torque Wrenches and Torque Wrench Quality

The plain truth is that the torque wrench method is not very accurate for tensioning a bolt. There are Torque angle meters and stretch meters that high end techs rely on more than a flat out torque wrench, however most people don't even know about these things and for us garage/home mechanics, that's out of our league anyway, so I am not going to go into the reasons why torque wrenches are not very accurate...ok I lied, about 40% of the force applied on a torque wrench is used to overcome friction, about 50% goes to overcome FACE friction, and the remaining 10% is applied to the load. Again way more than the DIYer should be concerned with.


A good torque wrench should not be something to be skimped on ESPECIALLY if you plan on doing a lot of work on your car, save you pennies and get a good quality digital torque wrench. I'm talking CDI, Snap-On, Mac Tools, etc. You can expect to pay north of $300.00 for one of these wrenches.

Craftsman torque wrenches are considered the very bottom of the barrel as far as torque wrenches go. Anything less than a Craftsman wrench is just plan crap, especially the Harbor Freight ones. Sorry you cheapies out there :bawling:, ROC wrenches are just $hit. (ROC=Republic of China)

Getting a rental torque wrench really is not a good idea either :thumbdwn:, as you have no idea what condition that torque wrench is in. Did the person before you drop it on the floor? Has it been stored correctly? A torque wrench should always be backed off to the "zero" setting for storage.

Here are the 4 types of torque wrenches.

:eeps:Beam:eeps:

This type of torque wrench goes way back in history. It is the oldest style of the group here. A beam is attached to the head of the wrench that goes down to the handle in the form of a needle. When torque is applied, that beam will move along a scale marked with torque values. The User needs to observe when the needle reaches the desired torque.



:)Clicker:)

Probably the most common type. The user twists the handle to raise it to the target torque that is stamped on the side. Once the handle is set, the wrench will "Click" giving the user an audible indication that the target torque has be achieved.





:clap:Dial:clap:

Considered by many to be the most accurate. And like the beam type, torque value must be observed. Usually the bezel has an indicator that the user can turn to mark the desired target torque so it is easier to see when the torque needle is reaching that target.





:bow:Digital:bow:


Digital torque wrenches are by far the best types you can get, but also the most expensive. They will make a tone and sometimes light up when a preset torque is achieved. The nice thing about a digital, is you can change values on the fly. You can at the push of a button, change to inch pounds, foot pounds, Newton etc. Higher end digitals will even do bolt angles. Some can store your torques to be later downloaded to a PC program, but these types are more for the professional mechanic.


here is a short video on the proper use of a clicker.
https://www.youtube.com/watch?v=qoOgSeKsFyg


Note: As I recently found out at the cost of experiencing the tensile strength (i.e. broken bolt) of my VANOS set bolts, Not all torque wrenches will operate the torquing of left handed threaded bolts. Be aware of this.


E46 Fanatic Gatriel did an awesome writeup on Torques and how they apply to the E46 CLICK THIS to see his post.


Ok, wrapping this up

This post really just touches on the subject of nuts and bolts, and is very elementary in its content. I wanted to learn more about nuts and bolts for myself so I could have a better understanding of the subject. I wanted to share what I had learned with my fellow fanatics that may have some interest in this area as well. Anyway thanks for reading.





Definitions

Clamp Force: the cumulative compressive normal force generated between joint members due to the tensile force created in tightened fasteners

Preload: The tension created in a fastener when it is tightened
Proof Load: An axial tension load which the product must withstand without evidence of any permanent set.

Tensile Strength:
The maximum load in tension (pulling apart) which a material can withstand before breaking or fracturing

Torque: a rotational force or twisting motion that causes torsion or rotation and is given in units of pound-feet or newton-meter

TTY: Torque To Yield-A limited or single use type of bolt

Yield Strength: The maximum load at which a material exhibits a specific permanent deformation.






References

aa1car.com
Bently Manual
boltdepot.com
boltscience.com
fastenal.com
felpro-only.com
hotrodders.com
Moss Motors
smartbolts.com
wikipedia.org​
 

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Jesus, that's a dissertation. Although you know like 10000 times more than I do about that stuff I still disagree about HF torque wrenches :) What can I do? I love cheap HF stuff :)
Thanks for a write up.
 

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Nice work dude. I replaced my lower subframe bolts - once. If you don't TTY then when installing, do they last longer? They are not stretched! I know they are supposed to snap in the event of a crash and that is why they are TTY (or that's what I've heard) - to make the engine move down instead of at you, but is that true?
 

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This is all great info! Thanks for taking the time to write this up, as this will be useful not only on the E46, but everywhere else you use nuts and bolts.
 

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Nice writeup, thanks for doing it. Reminded me that I haven't had my torque wrenches calibrated in a long while. I liked the home calibration video too, thanks jfoj. Was that a Harbor Freight calibration gauge? Gotta get me one of those. The calibration shop I used charged $75 a piece but that was industrial and an ISO requirement so probably overpriced.
 

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Discussion Starter · #18 ·
Nice work dude. I replaced my lower subframe bolts - once. If you don't TTY then when installing, do they last longer? They are not stretched! I know they are supposed to snap in the event of a crash and that is why they are TTY (or that's what I've heard) - to make the engine move down instead of at you, but is that true?
Trizzuth, Its true that auto manufatures build in Crush/crumple zones. Most do engineer some sort of engine deflection to keep it from going into the passenger compartment.

The reinforcement plate is part of the frame structure of the car. This is why BMW put TTY bolts here because of the plates importance to the frame. TTY bolts are not the same as Shear bolts. Shear bolts usually have a weak point built into them that will break on purpose if a certain stress is reached. Pictured below are examples of shear bolts.

 

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Thanks for the write up KaktusJaque, really good info here.:thumbsup: Proper torque wrench storage and calibration is also very important. They should be professionally calibrated once a year or anytime they take a hard hit. When stored they should always be set to zero and unlocked.
 

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And your bolts for that matter!

How well do you know your nuts and bolts?
What do those markings mean on the head of the bolt?
What exactly is torque anyway?
How does locktight or oil affect torque?

Well the questions can go on and on, so I wanted to do a write up to answer those questions above and a few more. Once you have a better understanding of your nuts and bolts and some nitty gritty behind the science of them, you will have a better appreciation of how this applies to you and your car. Note: I am keeping this post very simplified because this subject can easily get very in-depth and boring quite quickly.




Boltology and Nutology 101

I wanted to first start out by briefly getting into why a bolt or nut says in place. Bolts and nuts do not merely stay in place just because they are tight. There is a whole lot of physics and science behind this with a lot of Greek letters and algebraic variables, and if you are into this sort of thing (which I'm not), the information can be easily found with simple searches, As I stated, I am not into all that and as such, I do not want to introduce that bore here, besides I was never that good at that kind of math anyway.

So quite simply, bolts stretch when torque is applied. Like a spring or rubber band that is stretched, the natural tenancy of a bolt is to retract back to it's normal (static) condition.

When components are bolted together with this tenancy to retract, this creates a condition known as the "clamping force". It's this clamping force (and friction) that keeps a bolt or nut in place.

If a bolt or nut is torqued too much, the bolt will stretch more than it was designed to and will not be able to retract back thus lessening the clamping force that is specified for that bolt.

If a bolt or nut is not torqued enough, then again the clamping force will not be achieved, and the bolt can loosen itself.

This is why having a good quality torque wrench is vitally important. Notice I said good quality, but I will get into that later. By not using a torque wrench to tighten your nuts and bolts, you are setting yourself up for eminent failure of that nut or bolt.

Here is a very good 10 minute video explaining torque if you are so inclined to watch.

https://www.youtube.com/watch?v=3E42q4hYJ8I

The top reasons bolts and nuts fail are
Overloading
Overtorquing
Undertorquing
Corrosion


Bolt Styles and Types

As a DIYer, you will encounter several different types of bolts/screws. Below is a chart of the nomenclature of what you might see.



I have not seen any Slotted or Square drive type bolts/screws on the E46, however the Torx is quite
common
.


Bolt and Nut Grades
Have you ever noticed that bolt heads have lines or numbers on them and wondered what the heckfire do those mean? Well my friend, you have come to the right place to get some education. Nuts and bolts are graded on the material that they are made of. The larger the grade the stronger the bolt/nut. US bolts or SAE have a different grade rating system than their metric, or ISO, counter parts, however the same holds true for metric, the larger the grade the stronger the bolt/nut. Also, the higher the grade, the higher the torque that can be applied.


Here is a chart of the most common Metric bolt markings.



Here is a chart of the most common SAE bolt markings.


There are more grades than what are shown in the pictures above, these are just some common ones. You may see letters also stamped into the heads. These letters have different meanings, typically indicating a manufacture. One exception to the letters is "TTY" You may come across this as you do your own work on your car. TTY will be a topic of discussion a bit later.

Note: Metric 8.8 is equivalent to SAE 5, Metric 9.8=SAE 7 and Metric 10.9=SAE 8

Nuts too have markings to indicate their craft material and strength levels, however Identifying nuts is not as easy or straight forward as bolts are. As with bolts, the higher the grade the stronger the nut.







Time to talk TTY, no it's not the teletypewriter! It's Torque To Yield

Ok, many of you's here have no clue as to what this is, some of you do, but do not care, and others are quite knowledgeable about TTY Bolts.

This is a critical subject, so pay attention boys and girls!

There are a few places on your E46 that have TTY bolts, such as the reinforcement plate, Control Arm and suspension components, Engine block /head just to name a few.

Basically these type of bolts are used in areas of high frequency high load situations that have a higher risk of fatigue related failure.

If you are using the Bently manual :read: for instruction for the task you have at hand, you will know a bolt is a TTY bolt when the manual plainly states. "Replace Bolt" even though this statement seems unambiguous, you would be wise to heed it's simple warning.

The reason these bolts need to be replaced after a single usage is that they are engineered to stretch within a controlled yield zone. Once they reach this zone, they are designed to spring back to provide a more precise level of clamping force. This stretch approaches the bolts' elastic limit which permanently stretches it, therefore they cannot be used again.

Did you catch that?! They CANNOT be used again.

As mentioned before, TTY bolts are used on the reinforcement plate, there are 8 of these bolts for you non Xi types. The reinforcement plate is a part that is frequently taken off to work on the underside of the car.



I would venture to say :eek: that most home mechanics like the one that you are, do not replace these bolts, you just reuse the old ones. This is a common noob mistake. Each time these bolts are reused, they become more weakened than the time before, and because this reinforcement plate is a critical component to your cars frame and suspension, you are just inviting trouble to dinner. Do yourself a flavor, and buy extra of these bolts and just keep them on the shelf for future work. I know it sucks to get the plate off and not have replacement bolts on hand, maybe you didn't think ahead, or the job was last minute. In either case, it just means you're going to put the old ones back on, because you do not want to, or cannot wait for new ones to come in the mail, or you can't get to the dealer to pick them up.
Here, Ill help you out, here is a link to these bolts. (Verify proper fitment to your car first however).
The 30 bucks or so is very little to ask as compared to a repair job for a screwed up front end of your car, that's if it is even fixable.







To add or not to add....lubricant/threadlocker

Lubricant

You may read in places that oil is added to bolts and nuts, like studs on engine block for example. If you pull up torque charts for various bolts, you will likely see two values, a wet one and a dry one. Dry values will have a higher torque numbers. The reason being, oil will change the amount of torque needed to stretch a bolt by reducing the friction over that of a dry one. The oil gives a more even torque around the entire thread of a bolt. So why not just put oil on all you bolts then? Most bolts that the normal DIYer will be dealing with have a larger safety zone between the safe torque (aka, proof load) and the overtorque range (aka yield strength). Bolts that have a smaller zone between proof load and yield strength are the types of bolts that oil benefits. This is common in spacecraft/aircraft. Simply put, lubrication allows the bolt to be placed closer to it's yield strength. This just is not necessary in most cases for the E46




Threadlocker

Commonly known as Loctite. Loctite is a chemical thread locking compound. In addition to thread locking, it also has corrosion inhibitors, reduces friction, provides 100% contact between the metal parts, and reduces galling. When you use a threadlocker, it is reported that you use the dry torque values, not the wet as we talked about above. There are several different types of Loctite that you need to know about. You do not want to use the wrong type for your application.


Note: Never use red unless you have to for a specific reason to do so

This chart depicts the "Loctite" brand and their system, however, knockoff threadlockers usually use the same numbering system as Loctite. Red is sometimes referred to be permanent because of it's strength properties. And it has been reported that heads of bolts treated with a red loctite have snapped off because the hold is so strong. However if the bolt is heated up to the Loctite temp range, the bolt will release.





Torque Wrenches and Torque Wrench Quality

The plain truth is that the torque wrench method is not very accurate for tensioning a bolt. There are Torque angle meters and stretch meters that high end techs rely on more than a flat out torque wrench, however most people don't even know about these things and for us garage/home mechanics, that's out of our league anyway, so I am not going to go into the reasons why torque wrenches are not very accurate...ok I lied, about 40% of the force applied on a torque wrench is used to overcome friction, about 50% goes to overcome FACE friction, and the remaining 10% is applied to the load. Again way more than the DIYer should be concerned with.


A good torque wrench should not be something to be skimped on ESPECIALLY if you plan on doing a lot of work on your car, save you pennies and get a good quality digital torque wrench. I'm talking CDI, Snap-On, Mac Tools, etc. You can expect to pay north of $300.00 for one of these wrenches.

Craftsman torque wrenches are considered the very bottom of the barrel as far as torque wrenches go. Anything less than a Craftsman wrench is just plan crap, especially the Harbor Freight ones. Sorry you cheapies out there :bawling:, ROC wrenches are just $hit. (ROC=Republic of China)

Getting a rental torque wrench really is not a good idea either :thumbdwn:, as you have no idea what condition that torque wrench is in. Did the person before you drop it on the floor? Has it been stored correctly? A torque wrench should always be backed off to the "zero" setting for storage.

Here are the 4 types of torque wrenches.

:eeps:Beam:eeps:

This type of torque wrench goes way back in history. It is the oldest style of the group here. A beam is attached to the head of the wrench that goes down to the handle in the form of a needle. When torque is applied, that beam will move along a scale marked with torque values. The User needs to observe when the needle reaches the desired torque.



:)Clicker:)

Probably the most common type. The user twists the handle to raise it to the target torque that is stamped on the side. Once the handle is set, the wrench will "Click" giving the user an audible indication that the target torque has be achieved.





:clap:Dial:clap:

Considered by many to be the most accurate. And like the beam type, torque value must be observed. Usually the bezel has an indicator that the user can turn to mark the desired target torque so it is easier to see when the torque needle is reaching that target.





:bow:Digital:bow:


Digital torque wrenches are by far the best types you can get, but also the most expensive. They will make a tone and sometimes light up when a preset torque is achieved. The nice thing about a digital, is you can change values on the fly. You can at the push of a button, change to inch pounds, foot pounds, Newton etc. Higher end digitals will even do bolt angles. Some can store your torques to be later downloaded to a PC program, but these types are more for the professional mechanic.


here is a short video on the proper use of a clicker.
https://www.youtube.com/watch?v=qoOgSeKsFyg


Note: As I recently found out at the cost of experiencing the tensile strength (i.e. broken bolt) of my VANOS set bolts, Not all torque wrenches will operate the torquing of left handed threaded bolts. Be aware of this.





Ok, wrapping this up

This post really just touches on the subject of nuts and bolts, and is very elementary in its content. I wanted to learn more about nuts and bolts for myself so I could have a better understanding of the subject. I wanted to share what I had learned with my fellow fanatics that may have some interest in this area as well. Anyway thanks for reading.





Definitions

Clamp Force: the cumulative compressive normal force generated between joint members due to the tensile force created in tightened fasteners

Preload: The tension created in a fastener when it is tightened
Proof Load: An axial tension load which the product must withstand without evidence of any permanent set.

Tensile Strength:
The maximum load in tension (pulling apart) which a material can withstand before breaking or fracturing

Torque: a rotational force or twisting motion that causes torsion or rotation and is given in units of pound-feet or newton-meter

TTY: Torque To Yield-A limited or single use type of bolt

Yield Strength: The maximum load at which a material exhibits a specific permanent deformation.






References

aa1car.com
Bently Manual
boltdepot.com
boltscience.com
fastenal.com
felpro-only.com
hotrodders.com
Moss Motors
smartbolts.com
wikipedia.org​
You're gonna go blind if you know your nuts too well.
 
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