How to fix your car or van safely
What do we mean here by "Safety"?
There are two types of safety involved here: safety when actually doing the job and the safety of the vehicle once the job is done. This hub addresses both of these.
Use the right tool for the job.
Using make-do tools frequently ends up in tears because you hurt yourself, break a piece of the car or - more frequently - both.
Some essential tools
Use a solid support
If you have to jack the car up, put a solid support - such as axle stands - under it. Gently lower the car on the jack until most of the weight is resting on the stands. You can leave the jack there to take some of the weight, thereby subjecting all the supports to less stress. Whilst we're here, make sure the jack has sufficient oil in it and if not, only top it up with oil meant for the job - car engine oil will not do.
Know what you're doing
For all but the simplest jobs, before you start, get the workshop manual and read through the details of what you're going to do. Make sure you have the right tools. Have a look at the bits you're going to be working on before even picking up a tool and make sure it matches what's in the manual. Those books aren't infallible and your car may not exactly match the book.
Make sure you can see
Especially if you're working under the car, use a powerful light but make sure you aren't going to get a hot piece of worklight dripping on your head! Eve in bright sunlight, it can be very dark working under a car or behind an engine. The sunlight makes your eyes' pupils close down, letting less light into your eyes and so you can't see the dark parts as well as you expect to. So you need the worklight! Wear eye protection when working under the vehicle (or upside down in a footwell!!) - dirty, gritty oil in your eye stings and can cause blindness.
Don't force things
If a fixing won't move when you try and remove it with the right tool, check the torque that should be used to tighten it. Mostly, the torque to undo it won't exceed two or two and a half times that (those figures are from my experience and there may be better ones out there somewhere). Use WD40 or a similar unlocking fluid before you try and undo what may be an obstinate nut or bolt. Leave it on for at least an hour - overnight is better - and apply some more before actually attacking it with the tool.
Beware of putting so much force on a tool that you break the fastener. The suddenly-released force when the fixing breaks can cause you to hit something hard with a part of your hand or arm. This can result in nasty gashes, perhaps needing stitches, and even broken fingers and limbs. It's more common than you may think. In some cases, you can put a folded towel where you might hit your hand if the fixing "lets go", or wrap it around your hand. Wear work gloves as well.
Use barrier cream and work gloves or rubber gloves
Many of the oils used in motor vehicles are very bad for your skin - they can cause all sorts of unpleasant reactions and, in extreme cases, cancer. A good barrier cream will pretty much prevent such effects. Wear rubber gloves as well when doing precision work, heavy leather work gloves for the brute force stuff.
Use the right fixings
If you need to replace a nut or bolt - or any other fixing - make sure you use the right one. This is particularly true of highly stressed bolts such as those used on cylinder heads or some suspension components. If the manual says that new fixings should always be used then put the old ones in the recycling bin and get the new ones. Ignoring this will probably lead to expensive damage and can be fatal - especially true of disc brake calliper bolts!
Use a torque wrench
If you over-tighten a nut or bolt then it may fracture under the stress of normal use. Again, this can be expensive but can also be fatal. It is imperative that, for most fixings on a motor vehicle, they are tightened to the correct torque. Buy or rent a torque wrench and get the correct settings for the fixings you are dealing with.
When tightening some bolts, such as on a cylinder head, not only must they be tightened in the correct sequence but it often has to be done in stages. That will sometimes involve not only a torque specification but also turning the bolt through a particular angle at some stage. Failure to observe such instructions when working on modern high-performance engines can easily lead to expensive damage. If you get an engine blowout in the middle of an overtaking manoeuvre, for example, the results are generally not pleasant!
Use thread sealant
This is especially true when dealing with safety-critical fixings and those subject to high levels of vibration. Examples are brake fixing bolts, engine Main Bearing bolts and some major suspension components. It can also be used even when not specified to give an added margin of safety - but be careful as the manual may specify that, in some places, it must not be used.