What a tool
What is a torque wrench, what is it for and how do you use it?
Getting to 6 the plugs
Plugs are getting more and more difficult to find these days. You might have to remove some more parts of the air intake to get access to the spark plugs. If so, there may well be sensors connected to it, so watch out for any bits that might need disconnecting. Some bikes even need the engine to be removed to get the plugs out (2005 Kawasaki ZX-10R, for example). If you are struggling to access them, think outside the box. Sometimes they can be accessed from the front, which often means removing the exhaust and radiator. Once you have got everything out of the way, you should be able to locate the plugs.
Removing the 7 coil sticks
Unplug the electrical connecters at the top of the coil sticks, but before you do so, it is a good idea to number the connectors, so they go back on the right cylinder. It can get a bit dusty in the area, so it’s a good idea to blow everything off with some compressed air, if you have the means, as once you remove the coil sticks and plugs, anything in the vicinity can drop into the combustion chamber. If the plugs haven’t been out for a while it’s likely that the coil sticks will be tricky to remove; there is a seal in there which can become really tight over time. Try and remove the coil sticks with your hands at first, gently working some
movement into them. Using tools is more likely to damage things, but if you need to, you might have to enlist the help of a big flat screwdriver to lever the sticks up, being careful not to snap anything. If you have a much older bike then the coils will be somewhere else, and it will just be a case of unclipping the HT leads off the top of the plugs.
8 Removing plugs
If you have a set of spark plug sockets, there ought to be one that fits, but it isn’t always the case so you may have to resort to using a normal ‘deep’ socket. You will likely need an extension too, possibly with a universal joint in it. The plugs ought not to be too tight so it shouldn’t be too difficult removing them. If you’re using spark plug sockets, they should grip the plug and pull it out the hole, but if you are using normal sockets, you may need to use a magnet or piece of hose to help you lift each plug out the hole.
9 Checking the plugs
The first thing to do is have a visual check of the ceramic insulator – if it is cracked at all, the plug is no good. An old (or high mileage) spark plug could be heavily corroded; the spark occurs between the centre and outside electrodes which causes both electrodes to corrode, which increases this gap. The bigger the gap is, the harder work it is for the spark to bridge the gap, so it is important the gap is correct. Each plug will have a tolerance for the size of the gap, and will be something like 0.6mm-0.7mm, which can be checked with a feeler gauge. All the plugs should look roughly the same. If there is one that looks different to the rest, it could be evidence of something strange going on in that cylinder. Perhaps there is an air leak on an inlet, a badly seated valve or worn piston ring.
10 Replacing plugs
There are different options when it comes to replacing your plugs. If your current ones are in good nick with the correct gap there's nothing wrong with re-fitting them (if you are re-fitting the old plugs, you should replace the washer ,as it’s this which forms the seal between the cylinder head and the plug). Alternatively, the plugs you remove should have a code on them, which will help you find a like-for-like replacement. For extra performance, you can pay a bit more and fit some iridium or platinum plugs. Beware of cheap, knock-off sparkplugs, though. If you find spark plugs for less than £10 a piece, they are probably not genuine. Before you fit new plugs, always have a really good visual check of them. Most plugs come pre-gapped, but it is a good idea to check the gap with a feeler gauge, because if they've been dropped, the gap could well be out of spec. If you need to, you can gently adjust the gap with a small screwdriver. It's also vital that you don’t get them cross threaded, so a good tip is to use a little piece of hose to get them started. Simply push the hose over the top of the plug, lower into the hole until its sat on top of the threads, and turn the hose until the plug starts to screw in. Then, if the threads do get crossed up, the hose will twist before any damage is caused to the cylinder head. Once the treads are started, whizz them in with your fingers, before tightening each of the plugs down with a torque wrench, set to whatever the manufacturer’s settings are. The torque settings will be fairly low, but don't overtighten the plugs as you can easily strip the threads or damage the plugs.
Replacing coil 11 sticks
It is worth popping a little bit of grease on the seals of the coil sticks when you replace them, for two reasons; firstly, because it makes it easier for them to push into place, but most importantly, it will make life a lot easier when remove them next time. The coil sticks are dead easy to slot back in. Just drop them into the plug holes and push down until they stop clicking. They should be sealed around the top, and once pushed down, should all be the same height. If one isn’t sitting down as neatly as the rest, give it another push or whip it out and try again. When all the coil sticks are in place, re-connect the electrical plus to the tops of the coil sticks. It is hugely important that you connect the correct lead to each cylinder.