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Old 08-16-2011, 02:35 PM   #1
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Fastener Info: Rounded-Off Bolt Heads, Stripped Threads, and Seized Bolts

Having dealt with a few different german cars with build dates from the past 3 decades, being a mechanical engineering major that finds fastener technology and their physics interesting, a machinist, and a battlebot builder here are some tips that will save you a lot of headaches, possible injuries, and frustration.

A. Bolt head styles to watch out for
B. When to take extra action on a rounding bolt head
C. How to loosen a seized bolt with a head that is starting to round
D. Dealing with stripped threads
E. Preventing seized fasteners, rounded heads, and stripped threads



A. Bolts head styles to watch out for:


1. The Allen head bolt!
These fasteners are wonderful for applications with limited space where their is not enough space to insert a tool, the fastener is recessed within a hole, or the bolt head must be flush to the surface. Commonly these fasteners are made in higher grade(stronger) than other fasteners. Because of all these good features, they tend to show up a lot, more on some cars than others. When it comes to applying torque to these fasteners, they are absolutely horrible because of how small the surface is that you are applying torque to. Take extreme caution with these bolts all the time, as they frequently have considerable installation torques, by nature are easier to strip, and can be very hard to remove if rounded.


2. Phillips and Pozidriv and other
Stupid design in my opinion that is actually designed to have the screwdriver cam out when enough torque is applied to it to prevent damaging the clamping piece. They are so common they show up in a lot of places. Take moderate care with these.


3. Slot or flathead
Annoying to deal with because the design does not center the driver making installation and removal slower and more difficult, but they do have the advantage of applying more torque. The fact that these do not align the tip of the driver axially or concentrically can make them strip easily if care is not taken, in addition to the greater torque they may have to start. Take moderate care with these but if good practices are taken, rarely an issue.


B. When to take extra action on a rounding bolt head:

As early as possible! If your wrench, driver, ratchet, etc... felt or looked like it moved but that bolt didn't, STOP. See if the head is showing indents or rounding of corners. If rounding is showing, do not give it "one more try" or you will be in trouble.


C. How to loosen a seized bolt with a head that is starting to round (from least to most destructive):

1. Check to make sure the bolt is actually able to rotate out. Make sure the two pieces being clamped together are aligned and aren't shearing the bolt. Make sure your wrench or tool isn't contacting anything. Think about whether the part may have Loctite on it or not (if so, heat the bolt up until water boils on contact to disable the Loctite). Check to make sure there isn't anything that is actually keeping the head in place and preventing it from rotating.


2. PB Blaster. It's not hard to find if you live in the US, available in most hardware and automotive stores, and not very expensive. It is not designed to lubricate like motor oil, it is not designed to displace water like WD-40, it is a penetrating lubricate that is designed to wick into thin cracks through capillary action and do a small amount of dissolving, and for that reason you don't let it get on any rubber, plastic, or painted surface. Spray it on, wait 15 minutes, then attempt removing the bolt. Can be left on longer if you are in no hurry and don't want to damage the bolt, as this is your last non-destructive option.


2.5. Try a manual impact screwdriver sort of a half step between on the verge of being destructive and not. It does much of the same as hitting the head of the screw with a center punch like below, but imparts a turning motion at the same time. Put the correct attachment on the impact screw driver, line it up centered, and hit it with a steel hammer. If only a light tap is needed, frequently no bolt damage is done, but damage is definitely possible with harder hammering. Also if using this on sockets, it's somewhat debatable that you should use impact sockets just like a full on impact gun, as normal hand sockets are not designed for impacts and can sometimes shatter.


3. Use a center punch, and a steel hammer, place the tip of the center punch in the middle of the bolt head, and give a big whack. That small jolt is often all that is needed to loosen light corrosion of the threads. This method does not work if the item threads into something soft or light weight, like a door panel screw or a small sensor you have in your hand. Throw away bolt once removed.


4. This method may not be applicable to all situations, as it involves a lot of heat. You take a hand held torch and heat the bolt until it is just barely glowing red, then give another whack with the center punch and hammer like above. You cannot use a lighter or a little kitchen torch, but an actual torch used for construction as pictured above because you want to put a lot of heat into the fastener fast. Let the bolt air cool to the touch and try removing again. Beyond this point, you might as well turn your wrench, ratchet or driver as hard as you can because the bolt head shape is no longer of any use to us. Throw away bolt once removed.


5. Clamp some Vise Grips onto the bolt head, making sure the vise grips will not slip, and turn very hard. You are now running out of options. Throw away bolt once removed.


6. Use a screw extractor, ideally with a left handed drill bit. You should already have a small dent in the center of your screw from the center punch (since this is actually what a center punch is normally used for) that should allow you to start your hole with the left handed drill bit. Screws are usually pretty hard steel, and material is removed slowly, and as a result the drill bit will get hotter than if you cut something softer like wood, plastic, or aluminum. Don't let the drill bit get too hot or you will ruin it! Keep drill speed slow, apply as much controlled pressure as you can, and stop every few minutes to cool the drill bit with anything, motor oil, simple green, water, WD-40, etc... You don't want the drill bit getting hot enough that it changes colors or it will most likely be ruined. If you are lucky, the bolt may just come out here since pressure will be relieved from the threads and the grabbing action of the drill bit will want to turn the bolt. If not, lightly tap in the extractor, and using an adjustable crescent wrench, or ideally a tapping wrench, unscrew the bolt. Make sure you don't break either the tap or the drill bit, or you have made your problem even worse. Throw away bolt once removed.


7. The following method has an almost guaranteed chance of damaging other nearby items, so I am usually against this one. Take a Dremel or other similar small rotary tool and cut a slot into the head of the bolt to turn it into a slotted bolt head. Make sure the slot is as deep as possible, and narrow enough to get a good fit with a slotted screwdriver. Throw away bolt once removed.


D. Dealing with stripped threads

There is only one thing to do at this point, replace the threads. If a bolt already pulled out once, chasing the threads with a die or tap won't do much good. If the bolt, nut, or stud, simple unscrew and replace. If the stripped threads are the female thread tapped into something much larger, things are going to be more difficult. Your best bet is to look into something called a Heli-Coil or Time-sert. The directions vary slightly between whichever thread repair you choose. You want to make sure this is done absolutely perfectly or else they will pull out and you are left with an even larger unusable hole. If you do it right, the threaded hole should be stronger and more wear resistant (if tapped into a soft material like aluminum) than before.

E. Preventing seized fasteners, rounded heads, and stripped threads

1. Always use a torque wrench when installing the fastener. Tightening the fastener more than it needs to be makes it harder to get out later, risks damaging the part being clamped and risks damaging the bolt. Tightening the fastener less than it needs to be makes it much more susceptible to loosening and failure. The only place I frequently skip this are very small fasteners, where I simply stay on the side of tightened "just barely enough", as these fasteners are often holding something flexible and non-critical.

2. Make sure the threads are clean and can be threaded all the way by hand. Unless you are using a locknut, this should almost always be the case. If there are particles, contaminants, or grease on the threads, CLEAN THEM OFF, BOTH MALE AND FEMALE THREADS, and prevent it from getting on the threads to start. I like to spray the threads with Loctite 20162 ODC-Free Cleaner and Degreaser, and then remove with compressed air since this is quick and doesn't cause flash rusting. WD-40 and a shop towel work ok. If there is light surface corrosion on a high temperature part like an exhaust stud, a light brushing with a stainless steel brush is all that is required. "Chase" the threads with a tap and/or die to if there is any stubborn corrosion, dirt, or damaged threads.

3. Use assembly lubricant according to either the repair manual or judgement. If the part is going into a high temperature place like an exhaust or brake rotor, a very small amount of high-temperature anti-seize compound is very helpful, the only exception is spark plug threads where I recommend against anything other than clean metal because this is also an electrical connection, and high vibration fasteners that use Loctite as any dirt or oil prevents the Loctite from working properly. For many other fasteners, a light brushing of clean 30 weight motor oil(the automotive industry standard for installing fasteners) is very helpful in making sure the fastener is torqued to proper clamping load and not just thread friction, as well as reducing the chance of galling from things like steel fasteners rubbing against aluminum threads.

4. If the fastener has deformed threads, damage, or bad corrosion, THROW IT AWAY. As Caroll Smith states in some his "to win" books, "if there is any doubt, throw the fastener in question into the nearest large body of water and see if it floats." Replacing a few bolts is a lot cheaper than what your time should be worth if you have to forcefully extract them later. Damaged fasteners are not only difficult to remove, but can fail and damage even more parts of your car.

5. Use the correct tools and use them properly. If the socket doesn't fit nicely on the bolt head, it will frequently round it off or at the least, damage the bolt head. This is also why we don't use SAE sockets and tools on Metric parts. Don't use a screwdriver that is too small for the screw. Avoid cheapo tools that don't fit well, a good example are how I have only stripped allen head bolts with my cheap Chinese made Neiko Allen socket set, and never with my nice German Wiha Allen keys, which also frequently require me cleaning the Allen socket out or the Wiha keys will have a hard time fitting. If it is a 6 point bolt, try and use a 6 point socket. Use the box end of your wrench when possible over the open end. Avoid ever using a crescent wrench. In addition to the right tools, use them with common sense. Fasteners aren't going to be happy if you try removing them with your tool at an angle.


Conclusion:
Hopefully you can avoid some of the mistakes I have made or this helps you with your current problem. Let me know if there is anything that has been left out!
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Old 08-16-2011, 02:42 PM   #2
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nice read
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Old 08-16-2011, 02:44 PM   #3
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maybe a bit offtopic but I'm missing one of the lugnut fasteners that fasten your rear taillight covers to the back of the car. Any idea where I can get it? I used the same size one that was indentical but it stopped fastening about 3 or 4 turns in. Does Bmw have their own special type of lug nut? 0.o
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Old 08-16-2011, 02:56 PM   #4
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Very good information. Another tool I would recommend for cracking tight screws loose is an impact screwdriver. When I worked as an automotive tech, I always used an impact screwdriver for corroded or tight rotor locator bolts on BMWs and Porsches. PB Blaster or Kroil are great to use in conjunction.



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Old 08-16-2011, 02:58 PM   #5
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Old 08-16-2011, 03:04 PM   #6
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Nice write-up, Miles.

+1 on the Impact Driver. It's great for seized rotor hold down bolts, which have those pesky internal hex heads.
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Old 08-16-2011, 03:09 PM   #7
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3. Slot or flathead
Annoying to deal with because the design does not center the driver making installation and removal slower and more difficult, but they do have the advantage of applying more torque. The fact that these do not align the tip of the driver axially or concentrically can make them strip easily if care is not taken, in addition to the greater torque they may have to start. Take moderate care with these but if good practices are taken, rarely an issue.
Great info, I would also add to slot heads that if the head is heavily corroded take extra care as one 'half' of the head can break off leaving you in a pickle
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Old 08-16-2011, 03:11 PM   #8
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maybe a bit offtopic but I'm missing one of the lugnut fasteners that fasten your rear taillight covers to the back of the car. Any idea where I can get it? I used the same size one that was indentical but it stopped fastening about 3 or 4 turns in. Does Bmw have their own special type of lug nut? 0.o
I think it is a standard M6 flanged hex nut. You can get them at the dealership or a fastener specialty store. You can find the part number here: http://www.realoem.com/bmw/showparts...59&hg=63&fg=20

If only goes on 3-4 turns(I'm assuming 180 degree turns), and it is an M6 flange hex nut like what it is supposed to be, you probably started to cross thread it. Make sure the nut is going on completely straight.

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Originally Posted by DangerousMind View Post
Very good information. Another tool I would recommend for cracking tight screws loose is an impact screwdriver. When I worked as an automotive tech, I always used an impact screwdriver for corroded or tight rotor locator bolts on BMWs and Porsches. PB Blaster or Kroil are great to use in conjunction.

http://thumbnail.toolking.com/thumbn...mpact_Bits.jpg

http://www.sears.com/shc/s/p_10153_1...2&blockType=G2
That is also a very good one I forgot, I'll try to fit it in to the post.

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Old 08-16-2011, 05:05 PM   #9
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Nice Miles! I hope this reduces the number of fastener issues.

I've been thinking of doing something like this on cooling, but I think there's a cooling thread already...maybe two or three!

Nice of you to do. Sorry for this long post congratulating you on your excellent contribution!
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Old 08-16-2011, 05:32 PM   #10
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Old 11-08-2011, 02:29 AM   #11
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for a great thread everyone should read
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Old 11-08-2011, 09:59 AM   #12
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God I hate when bolts and screws strip, you know you're having a sh*tty day when you have to deal with them. Great write up
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Old 11-08-2011, 10:24 AM   #13
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maybe a bit offtopic but I'm missing one of the lugnut fasteners that fasten your rear taillight covers to the back of the car. Any idea where I can get it? I used the same size one that was indentical but it stopped fastening about 3 or 4 turns in. Does Bmw have their own special type of lug nut? 0.o
My guess would be that you have the correct size nut, but it is the wrong thread pitch (check out the thread pitch section on this page, about 1/2 way down: http://en.wikipedia.org/wiki/Screw_t....2C_and_starts ). A nut with incorrect pitch will start, but will freeze up once all of the threads are engaged.
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Old 11-08-2011, 10:35 AM   #14
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Thats a lot of good info based on a whole lot of experience right there!

Here's something I'll add, a product called EZ-Grip.

http://www.ezgrip.net/


I work on military aircraft, and this stuff is like magic. The first time I used it I was blown away... Most of the fasteners on 4th gen fighters are those irritating hi-torque offset phillips, which are designed to make it easier to tighten, but not to loosen. I can't tell you how many screws there are to start with on the outside of an F-16, but a good amount of them seize and strip, and the bit just walks out of the screw head. Put a few drops of EZ-Grip in the head, and you can lean on the wrench with all your might until the screw breaks loose without the bit slipping at all.

Anyone who spends a decent amount of time working on machined needs to have a bottle of this stuff lying around, it's only 20 bucks. It works great on anything that's stripped, but particularly well on recessed hex heads and phillips. :thumb up::
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Old 11-08-2011, 12:14 PM   #15
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@ Mkodama - great info, and it is also great to meet someone who has as much (probably more) knowledge of fasteners as I do. Of course, most of my knowledge is useless to me now, since I moved from manufacturing to Banking Analyst.
In my former life in manufacturing engineering, I somehow became the go-to guy for broken/stripped/fvked up fasteners. Since you can't (or shouldn't) ship out a new $500k machine with a messed up fastener in it, it was something I dealt with a lot. I guess my patience was the main thing that made me the "most qualified" person to deal with these things. A few things I would add or re-emphasize are:
- If you think the bolt, nut, or screw is starting to seize up, then STOP, and escalate. That desire to give it "one more try" will almost always make things worse. I always made sure the floor techs knew this. If you are in doubt, then stop, and follow the suggestions listed above, starting with the PB Blaster.

- Use well made tools, especially for Allen head/ internal hex screws. Poor fit is probably the main cause of screwed up Allen heads. Wera, or some of the other European tools are the best. If you can't afford, or don't want to pay for the set (they are expensive), then at least buy the bits, and use them in whatever cheap driver you already have. The bit is the business end of the thing after all. You can buy a set of the bits off of Amazon for a decent price. The bonus is that they will last much longer than most Chinese crap, and won't screw up your fasteners. If you are using an Allen wrench that looks even a little rounded, it will make a mess. The same thing applies to socket wrenches. If you can't afford the set, then just buy the sockets you need, and buy the best ones you can find. One note - My experience with "Ball End" Allen heads is that they are weaker, and tend to break off at the undercut where the ball section starts. They may have gotten better over the years, but we banned them from the factory after having to extract a few dozen of them. I would avoid them.

- Patience! If you start to get pissed, and want to beat the crap out of it, then walk away. Kick the dog, punch your wife's car, yell at the neighborhood kids, whatever. But calm down, and go back to it.

- Properly applied heat can help, but you HAVE to make sure you are heating the fastener, not the part with the threads in it. If the threaded part heats up, then you are expanding the hole, and making the threads clamp down even more.

- Cold. Cooling down the metal causes it to contract. I had a lot of luck with either cooling down the fastener, or the threaded piece. This causes contraction, and gives you some space around the threads to allow the PB Blaster to penetrate. The extra space it creates is often enough to get the fastener out. I had rigged up a sprayer that could be attached to a can of Freon, which allowed me to shrink the area enough to get the fastener out. It can work miracles. This is my first choice for removing a stuck fastener.

- Easy-outs and other screw extractors. Two very important things to remember here. As the OP mentioned, a center punch is critical to getting the drill bit started in the center of the screw. Be careful, and drill slowly. Make sure you are drilling straight, and do not break off the bit! For the extractor - make sure you are using the right size. Most of the time, I have seen people using one that is way too large for the screw. The manufacturer lists the size recommendations for the drill bit and the extractor on the box. Follow their advice. And make sure you save the box or the instructions, so you have them the next time you have a problem. So many people fail to do this.

- use the proper holder for the screw extractor. The best thing to use is a T-handle holder for taps. I have seen people using vise grips or wrenches. This is bad, because the extractors are made of VERY hard steel. That also makes it VERY brittle. If you apply sideways pressure to it when you are turning it, it can break off. This will lead to a much bigger mess, because you need something even harder to drill the broken extractor out. A tap handle will allow you to apply pressure straight down on the extractor.

- One type of fastener you did not mention, but that I have experience with, is one with a captive washer (the washer is trapped on the fastener, as a one piece unit). These were introduced in the factory where I worked, as a way to save time, avoid waste, and reduce the chance of a loose washer ending up near electrical parts. I do not remember seeing them on a BMW, but it is possible. The issue with these is that the torque specs are lower than the same sized fastener and separate washer combo. One of my fellow engineers learned this the hard way, by introducing them on a production line without changing the torque specs. We went through a period of snapped off bolt heads on the line, and parts falling off in the field. Major mess. The issue is that the fastener has a section where it is narrower than a normal screw, where the washer is trapped. This makes it weaker in that area, and it requires less torque. So, if you encounter one on a BMW or some other car, be aware that it has a lower torque setting than expected. For example: an 8mm screw with a captive washer will have lower torque specs than a normal 8mm bolt, so look it up. **I may have over explained this whole thing

I am sure that there are plenty of people who have removed screws with all sorts of crazy methods, including me. But the purpose of the OP's advice, and my advice, is to help you to deal with the issue in the most effective way, on the first try. Just because someone managed to remove a screw with anything other than the proper tools, it does not mean that you can too. You might get it to work, but you just might screw things up more. This is something you want to approach with the best tools and methods possible, because if you are working on a $10k + car, half a$$ed measures can get very expensive.
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Old 11-08-2011, 02:10 PM   #16
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I agree with everything you said, MJLavelle, other than two things, but even so, great advice.
-If you heat up the metal around the screw, the hole will open up, not clamp down.
-Also, probably a little better for the environment and more attainable than freon, a couple of companies make aerosol cans with sprayers specifically designed for what you described, cooling a fastener. Wurth definitely makes a product like this. The aerosol does the same job, and isn't as nasty to deal with as freon.

I kinda want to try the freezing the fastener method after hearing how well it worked for you.
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Old 11-08-2011, 07:17 PM   #17
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I agree with everything you said, MJLavelle, other than two things, but even so, great advice.
-If you heat up the metal around the screw, the hole will open up, not clamp down.
-Also, probably a little better for the environment and more attainable than freon, a couple of companies make aerosol cans with sprayers specifically designed for what you described, cooling a fastener. Wurth definitely makes a product like this. The aerosol does the same job, and isn't as nasty to deal with as freon.

I kinda want to try the freezing the fastener method after hearing how well it worked for you.
You are right about the heat, of course. I had a longer entry there, and edited it down, and screwed it up. What I was trying to say was to NOT heat up the screw, because it will wedge in more. In my experience, heat is an issue because it is hard to keep it from transferring to the fastener as well. Now heating the part, and hitting the screw with a blast of freon will work great, but there are not many times it is practical to do all of that, especially on a car. But, that is why cold can be a lot better. It will not destroy finishes, or ignite other substances that are around.

My worst episode with a stripped out bolt was on a machine that was ready to ship out the door, when a final inspection found an Allen screw with a broken off ball end Allen wrench wedged it inside it. I was called out after other attempts had made things even worse. There were 2 trucks, and a rigging crew standing by to move the thing (it was a BIG, $500k machine). I spent 6 hours trying to get it out, without damaging or removing parts from a complete machine. When I finally got it out, I was so pissed, I threw it across the production floor, and it bounced inside the main electrical box of another nearly complete machine that was undergoing testing. Of course, it was live, with 480 volts running in to it through a 90 amp line, as big around as your wrist. It exploded inside that box, and when all was said and done, it destroyed $15k worth of electronics. THAT is when I learned patience.
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Old 11-17-2011, 08:52 PM   #18
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Originally Posted by qslim View Post
Thats a lot of good info based on a whole lot of experience right there!

Here's something I'll add, a product called EZ-Grip.

http://www.ezgrip.net/


I work on military aircraft, and this stuff is like magic. The first time I used it I was blown away... Most of the fasteners on 4th gen fighters are those irritating hi-torque offset phillips, which are designed to make it easier to tighten, but not to loosen. I can't tell you how many screws there are to start with on the outside of an F-16, but a good amount of them seize and strip, and the bit just walks out of the screw head. Put a few drops of EZ-Grip in the head, and you can lean on the wrench with all your might until the screw breaks loose without the bit slipping at all.

Anyone who spends a decent amount of time working on machined needs to have a bottle of this stuff lying around, it's only 20 bucks. It works great on anything that's stripped, but particularly well on recessed hex heads and phillips. :thumb up::
Sounds like a fun job, I would love to be able to work on those beasts, in fact I'd say perfect job because what's bad about touching, working and looking at F-16s while getting paid for it
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Old 11-17-2011, 09:21 PM   #19
RKiepper
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Originally Posted by mkodama View Post

5. Use the correct tools and use them properly. If the socket doesn't fit nicely on the bolt head, it will frequently round it off or at the least, damage the bolt head. This is also why we don't use SAE sockets and tools on Metric parts. Don't use a screwdriver that is too small for the screw. Avoid cheapo tools that don't fit well, a good example are how I have only stripped allen head bolts with my cheap Chinese made Neiko Allen socket set, and never with my nice German Wiha Allen keys, which also frequently require me cleaning the Allen socket out or the Wiha keys will have a hard time fitting. If it is a 6 point bolt, try and use a 6 point socket. Use the box end of your wrench when possible over the open end. Avoid ever using a crescent wrench. In addition to the right tools, use them with common sense. Fasteners aren't going to be happy if you try removing them with your tool at an angle.
A 3/8 socket is not suitable for an E12 torx bolt!! You WILL regret it!
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Old 11-17-2011, 10:22 PM   #20
MJLavelle
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Quote:
Originally Posted by qslim View Post
Thats a lot of good info based on a whole lot of experience right there!

Here's something I'll add, a product called EZ-Grip.

http://www.ezgrip.net/


I work on military aircraft, and this stuff is like magic. The first time I used it I was blown away... Most of the fasteners on 4th gen fighters are those irritating hi-torque offset phillips, which are designed to make it easier to tighten, but not to loosen. I can't tell you how many screws there are to start with on the outside of an F-16, but a good amount of them seize and strip, and the bit just walks out of the screw head. Put a few drops of EZ-Grip in the head, and you can lean on the wrench with all your might until the screw breaks loose without the bit slipping at all.

Anyone who spends a decent amount of time working on machined needs to have a bottle of this stuff lying around, it's only 20 bucks. It works great on anything that's stripped, but particularly well on recessed hex heads and phillips. :thumb up::
I took your word for it, and ordered a bottle of this stuff. I hope it works as well as you say!
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