Spark plugs are on of the few consumable parts in your motorcycle engine, and it's easy to forget about them.We're spoilt these days. Modern motorcycles have ignition systems which are very reliable, and they need almost no effort to stay in top form. Where older motorcycles needed careful attention to contact breakers, condensers, HT leads and the like, current motorcycles use ultra-reliable transistorized ignition systems integrated into the engine management system.
There's only one part that needs any maintenance, and that's the spark plugs. On a modern four-stroke motorcycle, they last well, but an inspection will reveal any problems and fresh plugs can sharpen up throttle response on a motorcycle with a high kilometer count. It's a simple job really, and good for the soul.
Check your motorcycle's manual for the intervals – the usual routine is to check them at a minor service (4,000 to 6,000km) and change them at the major service.
Like many jobs, getting access is half the battle. Even on some naked-bikes, you need to take off the sidepanels and tank to get access to the spark plugs. On a sportsbike with an under-tank airbox you'll probably need to take that off too. Remember the workshop basics: put tanks and panels well out of the way so you don't trip over the fuel tank or put your foot through a sidepanel. Take care with the fasteners – a lost or mixed-up screw can easily add an hour to the job, and make a note of which connectors and hoses go where on the tank. Once you're under the plastic fairing, find the plug leads. Our motorcycle is a little old fashioned – it has conventional dual coils with HT (high-tension) wires that carry the sparks from the frame-mounted coils to the spark plugs. Most modern motorcycles nowadays have plug-top coils where each plug has its own tiny coil mounted directly in the plug cap itself. Pull out the plug cap/plugtop coil. If you take off more than one cap at a time, make a metal note or take a digital picture of the plug wiring so you can put the correct connector onto the correct plug later.
Using either the spark plug key supplied with the motorcycle, or a proper plug socket from your socket set, loosen the spark plug off and unscrew. Check the plug for excessive wear, deposits or corrosion. Our plug here is fine, and could probably go back in with no problems. Note the oil deposits – many motorcycles leak a little bit of oil into the spark plug wells. So long as it's just a drop, there's nothing to worry about.
Get the new plug, and apply the smallest smear of copper grease to the threads. Pop it into the plug key/socket, and carefully insert into the plug recess, and start the thread. Turn it gently by hand until you're sure the plug is threaded correctly. A crossed thread in a spark plug hole is a truly miserable situation which needs some serious spark plug thread repair.
This one time when we really advise a torque wrench, unless you're a solid spanner man. Over-tightening the spark plug can damage the threads in the soft aluminum cylinder head, and under-tightening can lead to a plug coming loose, which is also bad. Get the proper torque setting and use it. If you can't find it, check the spark plug manufacturers website. Refit the plug cap/coil, making sure that any seals are in place to stop water getting into the plug well. A little bit of silicon grease can help keep the rubber fully sealed.