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.