A new plug, one from an engine that’s running properly, and one from an engine that’s got some serious issues.
Last issue we covered some basic maintenance tasks. In this installment, we’ll delve a little deeper.
Although the days of routine plug failure are well behind us, spark plugs—like oil, filters and tires—are expendable items, requiring periodic inspection and replacement.
Before we look at the plugs let’s cover a few basic rules. First: spark plugs should never be removed or installed while the engine is hot. There are exceptions to this rule, but for our purposes, the engine should be stone cold whenever you’re working with the plugs.
Second: You’re going to need two special tools to remove, install and inspect the plugs. The first is a dedicated spark plug socket of the correct size, the second is a spark plug gapping tool. For the latter, get the traditional wire type, as the sliding fit ones aren’t so accurate. Both are readily available through your favorite tool supplier or motorcycle accessory catalog. But why a dedicated socket? Spark plug sockets have inserts in them that protect the porcelain portion of the plug and prevent the plug from cocking in the socket, plus it’ll hold the plug in the socket, all of which makes removal and installation without damaging anything far easier.
Finally, if you don’t have access to an air compressor and blow gun, grab a can of compressed air (the ones used to clean computer keyboards work fine), some sort of anti-seize compound, and a small tube of Dielectric Silicone grease (both available at any auto parts store.)
Remove any extraneous parts, like the fuel tank or cosmetic covers, that may be in the way. Motorcycles generally use hard plastic plug caps, so removing them, along with the attached coil, is straightforward; grasp the cap (not the wire) and give it a twist as you apply gentle upward pressure. It should pop right off; if it doesn’t work, try wiggling it gently as you lift. In all cases, resist the temptation to yank on the wire—all that’ll do is break the connection and create more problems.
In some cases, a “stick” coil may be attached directly to the plug. To remove them, first remove any retaining bolts and disconnect the primary wires, then remove the coil using the twist and lift method.
Blow any debris away from the spark plug base. Lungs and a soda straw will get it done, if you’ve got nothing else. Then remove the spark plug. After a turn or three, the plug should spin out easily, though it’ll probably still require a wrench to turn it. If the plug puts up a fight, try a shot or two of penetrating oil but if that doesn’t do it, gently thread the plug back in and have your shop take a look at it. It’s probably fine; seized plugs are rare these days, but it takes some experience to tell the difference between a plug that’s a little stiff and one that’s galling the threads on the way out.
Now that the plug’s out take a moment to inspect it; the plug is a “window” into the combustion chamber, so careful observation can tell you a lot about how the engine is running. A rundown on plug appearance and how it relates to combustion would take up too much space here, so head on over to www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp, for appropriate color photos and descriptions.
Allow me to digress for a moment and point out that if you’re riding a stock motorcycle and it’s running well, there’s really no need to perform routine spark plug inspections. It’s just as easy to replace them when the time comes and avoid the extra work. That’s just my opinion of course, but it’s based on replacing thousands of plugs over the last 45 years.