To an experienced mechanic or engineer the art of using tools properly might seem to be so basic that it doesn't really warrant explanation. It is actually a considerable skill though and one that most people never get taught. The first time your average amateur mechanic comes up against a seized or corroded nut or bolt the chances are he'll break it, or the tool, whereas an experienced mechanic will remove it without even realising it was a problem.
Using Socket Sets
The essential thing to get right with these is to make sure the torque you are applying is in a straight line with the fastener. Start pulling to one side and the socket will twist off the bolt or round the head off. Your left hand (for a right handed person) will be holding the ratchet end of the socket bar and your right hand will be applying the torque. Never try and use a socket bar one handed. The job of the left hand is to counter any twist that the right hand is trying to apply. This gets more important when you are using extension bars to reach a hidden bolt. The left hand must always hold the extension bar in a straight line with the bolt. The harder the right hand pulls the harder the left hand must push to counter the twist. The same principles apply to using torque wrenches.
Spanners are easier to use than socket sets for most jobs because a spanner is a straight line tool rather than an L shaped one so it doesn't have a tendency to twist off the bolt. Spanners are designed to be used one handed. The length of a spanner increases with head size to maintain the proper torque on the bolt. Although critical bolts such as big end and cylinder head bolts need to be done up with a torque wrench you can do up most other non critical fasteners just by using the right sized spanner with a 'feel' for the correct pull. Using the same length socket bar with different sized sockets means it is very easy to overtighten or strip a small bolt or undertighten a large one. Always use a ring spanner rather than open ended one whenever possible. There is much less chance of rounding a bolt head off that way. Never use an adjustable spanner if any other tool will fit the job.
Dealing With Stuck Fasteners
How you attack a badly stuck fastener sorts out the pros from the amateurs. If a reasonable amount of force on the spanner or socket bar refuses to undo something the worst thing you can do is just keep pulling harder and harder until something breaks. Bolts that have been in place a long time can require much more force to undo them than the torque that was applied to do them up in the first place. The trick is to break the 'seal' of corrosion or gum from old burnt oil holding them in place without breaking them in the process. Here are the techniques you need to apply to get that recalcitrant fastener out in one piece.
Remove Things In the Correct Order
If multiple fasteners hold a component down then don't just remove each one completely until the last poor bugger is taking the entire clamping force that the rest used to share between them. It's hardly surprising that this last one will now be either impossible to shift without breaking it or the bolt or component itself will already be bent.
This is especially vital if the component is loaded by either spring pressure under it or loads from a compressible gasket. Cam bearing caps which go all the way across 16v heads are a good example. The Peugeot Mi16 ones hold both cams down at the same time against the pressure of the valve springs using 4 bolts. If you remove the first three bolts on a cap before touching the 4th then several hundred pounds of valve spring pressure will now be trying to bend the bolt and break the cap.
Step 1 - Break the seal
Undo each bolt a tad and then nip it back up to take the load off the others. Do this to each in turn. You've now at least broken the 'seal' holding them in place.
Step 2 - Remove progressively in the right order
Then remove each bolt one turn at a time so the cap comes off evenly and in a straight line against the forces acting against it. If one bolt is particularly stubborn then tighten the others up hard to take the load off it. Then try again and you'll probably find it comes out very easily. Similarly don't just remove each cap completely until one last end cap is trying to hold down both cams. Remove all caps together one turn at a time per bolt.
Remove bolts from timing covers, cylinder heads etc in a diagonal pattern. Don't just work round the component in sequential order creating more and more uneven load on the remaining bolts. Refitting needs to be done the same way - progressively.
Shock It Loose
A good belt on the head of the fastener with a hammer and drift will shock the threads loose and reduce the holding torque by 50% or more. A handy tool to have in your box is a length of brass or bronze about 8" long and 3/4" in diameter. Place one end on the head of the bolt and give the other a few healthy belts with a claw hammer. If you can get direct access to the bolt then just hit it directly with the hammer but make damn sure there is nothing breakable close by like a fragile bit of aluminium casting standing proud or you stand a good chance of smashing that in the process. The drift helps you reach hidden bolts and is also soft enough so it won't damage the bolt head. Try undoing it again. If it still won't come out then hit it some more. It can take a while to persuade a bolt that it's in its own best interests to undo without you having to get really nasty.
If the stuck item is a stud you can mash the end threads if you start belting it with a hammer. So first wind a nut on until the face of the nut is just proud of the end of the stud. Then belt the nut. Even better, wind two nuts on and tighten them against each other so you have double the length of thread engaged to hit against.
Turning Up The Heat
Belting a stuck fastener will free it 90% of the time. For the other 10% you need to get serious. Applying a camping Gaz burner or propane torch will heat up and expand the fastener and hopefully reduce the clamping force between the head of the fastener and the component. While the fastener is hot give it a few belts for good measure. Try undoing it again. Repeat. You need to be aware of what is in the vicinity of the fastener before you start melting everything in sight. If there are plastic components nearby, fuel lines, carpets, oil inside the component or anything else inflammable then don't.
Some people swear by it and others at it. Personally I've rarely used the stuff because I usually manage to remove fasteners with the other methods described here. If the threads are rusted solidly in place then the oil is not going to penetrate anyway. If there are gaps for it to get into then it might be of use. If time is not of the essence then by all means try it and let several applications of your chosen brew soak in over a day or two.
Dealing With Specific Fasteners
Hex headed nuts and bolts
These are the most common fasteners you are going to come across. There are plenty of techniques to help you remove stuck ones.
1) Use a 6 point socket in preference to a 12 point one.
12 point sockets are fine for most work and make it easier to get the socket on the bolt head. They have much less grip than 6 point sockets though and are much more prone to rounding off stuck bolts, especially in the smaller sizes. In fact for anything under 12mm I'd say always use a 6 point socket if you have one.
2) Use a surface drive socket.
These are sockets which bear on the flat of the bolt rather than on the corners. They have convex internal faces rather than flat ones. Not only will they almost never round a bolt off, they also have a fair tolerance on size so they still grip well on rusted bolts which have lost material from the head.
3) Use a smaller socket than the nominal bolt size.
When fasteners have been in place for a long time and open to the elements they can lose a significant amount of metal from the head due to corrosion. I've seen 13mm bolts that measured not much more than 12mm across the flats after 10 years in the front of an engine block. A 1/2" socket can be a better fit on an undersize 13mm bolt. Similarly a 5/8" socket can substitute for a loose 16mm one. A 3/8" socket is good for a worn 10mm nut. 6mm for a worn 1/4" - there are lots of permutations here. If you have a socket set with metric, imperial and even Whitworth sockets in it then pick the best fitting one for the job regardless of what the nominal size of the bolt is. In extremis you can hammer a slightly undersize socket onto a corroded bolt head. It might not do the socket much good but that's a cheaper fix than having to send the whole thing away to have the rounded off bolt machined out.
Allen And Torx Bolts
Allen and Torx bolts are female fittings where the tool goes into the bolt rather than over it. That leads to particular problems you need to be aware of.
1) Always make sure the recess is clear of mud, corrosion and debris. Have a good scrape round inside with a small screwdriver before fitting the allen key.
2) Make sure the allen key is fully engaged. It's much harder to be sure an allen key is fully inside its bolt than it is to be sure a socket is fully over a hex bolt where you can see what is going on. If you try to undo a stuck allen bolt and the key is only partly engaged then you'll round off the bolt or the key. Make sure the recess is clear then tap the key in with a hammer.
3) Allen keys get worn at the ends after much use. Grind the key shorter to remove the rounded ends and expose new sharp edges or buy new ones if yours are looking worse for wear. Use top quality allen keys. Unbrako is a good name.
4) If the bolt is starting to round off then you can hammer an oversize key in. A 1/4" key will normally remove a worn 6mm bolt. A 10mm key will remove a worn 3/8" one.
There's one fitting which has been the bane of my life for many years, probably because I've build a lot of engines which have it fitted. The Ford CVH engine has allen key taper plugs to seal the oilways in the block. They are made of fairly mild steel because that's soft enough to allow the threads to distort a bit and seal against the threads in the block. Trouble is once they get stuck fast they are so soft that an allen key just rounds off the hex inside them. The techniques to get them out can be applied to other fasteners.
1) Hammer the hell out of them before you try using an allen key. That will usually distort the hex edges so you have to hammer the allen key in too but that's no big deal and actually helps the key to be a good tight fit.
2) If the above fails then what will happen when you try to undo them is the allen key will just round off the hex inside the plug. Drill an 8mm hole right through the plug and into the oilway. Find an old 8mm bolt. Put that into the hole and weld it into place with a MIG welder. The heat from the welding will shock the threads loose and when you apply a 13mm socket to the head of the 8mm bolt the plug will wind out as easy as anything. Apply that to other stuck fasteners. Weld a 19mm nut to the head of a 13mm bolt that refuses to come out. Weld a nut to the end of a stuck stud.
Studs - The Two Nut Trick
To remove studs don't use stud extractors. They chew up the threads and destroy the studs as they remove them. Wind on two nuts and do them up tightly against each other. Use a spanner on the bottom nut and wind the stud out. If it won't come out with normal force then apply the hammer technique first.
So the bolt finally broke
Despite one's best efforts the occasional fastener is going to break. How to remove it depends on what remnants are left and why it broke. The main problem is when the remains are under the surface of the component the bolt is in and you can't get a pair of vice grips on the stub. If a bolt or stud snapped while it was being tightened then chances are the remains will not be tight in the female thread it's left in. In those cases you can drill a small hole into it and use an Easy-Out which is a left hand threaded removal tool. The tricky bit is drilling the pilot hole without slipping off and ruining the component the bolt is stuck in. That's much more easily done on a milling machine or pillar drill with a milling cutter rather than a drill bit which will slip off the jagged end of the bolt. Trying to do this in situ is not easy. One way is to clamp a piece of steel to the component with a pilot hole already drilled in it to guide your drill bit centrally into the bolt.
If the bolt snapped while being removed because it was rusted into its thread then an Easy-Out is unlikely to work. Let's face it, if the full strength of the top half of the bolt wasn't enough to remove the threaded bit then a smaller tool fitted into a little pilot hole isn't going to help either. Chances are you'll break the Easy-Out inside the bolt and end up in an even worse mess. The way out here is to mill the bolt out carefully and retap the threads in the component or to helicoil the component back to its original size if the threads are too damaged to be used. Spark erosion is a useful method but expensive and obviously needs the component to be taken to a specialist. Welding a nut to any broken stub that can be reached is a good plan as described above.
If you don't have the tools or techniques to safely remove a broken bolt then don't try. You'll just damage things further. Take it to a machine shop and have it done properly.
The bolts are all out but the component won't come apart
Are you sure all the bolts are out? Sometimes there is a hidden bolt the engine designer put in to try your patience. On the thermostat housing of the Peugeot 205 there are several obvious hex bolts and one sneaky allen bolt inside a recess which can be overlooked. Similarly I'm sure many people have struggled to remove the centre main bearing cap on this engine before realising there are two extra 8mm bolts which go in sideways from the outside of the block. If you've been wrestling with a component which refuses to come undone have another look all round it and make sure you haven't missed a fastener.
The gasket is holding the component in place
Old gaskets, especially ones with sealant applied, can hold things in place like superglue even after all the bolts have been removed. Sumps and rocker covers are good examples. Don't just bang a chisel or screwdriver into the joint and expect the component to come apart. You'll damage something, especially if it is aluminium. Get an old kitchen knife and work it into the joint. Once it's in work it sideways with a sawing motion to gradually break the seal along the length of the part. If the parts you are trying to release are aluminium on one side and steel or iron on the other then work the knife between the gasket and the steel/iron component rather than between the gasket and the aluminium component. Aluminium is very soft and you can damage it very easily.
There is more to come on this topic but I'll add it in due course.
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Last update April 2007.