Spark plugs or bright sparks? You be the judge
What is the difference between a spark plug in a four stroke wet sump lawn mower engine doing 2.8 to 3.2 thousand revs a minute, and a commercial two stroke chainsaw turning at 13 thousand revs?
Most people look at the thread pitch, diameter and reach of the plug and that is good enough. It is better to make a sale than miss out.

It is critical to remove grass & scrub from around a property.

It is critical to remove grass & scrub from around a property.

Well, your small four stroke has a spark plug with a higher heat range and a shorter reach centre electrode, designed to run hotter to burn off oil. This includes what bypasses the rings from the wet sump and ignites a myriad of stale to fresh fuel of differing viscosity containing ethanol, toluene, paint solvent, paraffin and wax, with all kinds of debris in the air cleaner; whether it’s foam, oiled foam, paper element, foam sock or pre-filter oil.
This plug is designed to run with a fixed advance ignition system, either to run a resistor or non-resistor type spark plug. The difference changes the timing at up to 1800 sparks per minute, while a four stroke fires every second stroke and has to ignite fuel in a cold engine from approximately 200 rpm with very little reserve voltage from the energy created by the pull starter. This is the reason the correct spark plug and gap is required to be used by the engine manufacturer. When emissions standards are to be enforced, this will be even more important.
What if someone fits a non-resistor plug which changes the timing into a large V twin engine, or worse still, a fuel injected engine designed to run resistor plugs? These engines have a series of sensors checking the engine temperature, load and air entering the engine, and most of them recalibrate the fuel mixture and spark advance until they work out the altitude, air density and load, and they reach operating temperature. They will continue to correct those parameters as the day progresses in order to produce the best possible fuel economy and least emissions, but they will not run properly if the wrong spark plug is fitted.
Now back to our large capacity commercial chainsaw – say it is fitted with capacitor discharge integrated circuit technology (CDIC), which means that it will not produce sparks under 12 to 1300 revs, overcoming kick back when starting. ‘Sounds like a lot of revs for a pull starter’, you say – well it is not if you have the plug installed and the engine is in reasonable condition. If the rings are shot you may have some trouble, but if you take the plug out and pull it over, you will find it impossible to attain the revs to produce a spark as the piston with the plug out acts as a shock absorber.
CDIC units usually have four or six internal coils set at different rev ranges, and are automatically controlled as detected from the magnetic pulses of the fly wheel to increase or decrease the ignition timing. This controls the torque of the engine and minimises emissions, because these units have spark limiters to control over revving which are generally set around 13 to 14 k revs, eliminating one in four sparks to cool and lubricate. The spark plug must be the correct resistor type, with an extended centre electrode exactly as recommended for the engine by the manufacturer.
Unfortunately, suppliers providing poor quality equipment to unsuspecting customers do not provide technical information, least of all the details of a quality equivalent spark plug. In some cases, it costs too much to provide technical information, let alone training to business’s own dealers or opposition dealers, who often service more of their products.
Political parties in Australia have talked about emissions standards for almost 20 years and never mention qualifications, standards and regulations regarding who can sell outdoor power equipment. In the early days it was self-regulating, and dealers had a duty of care to provide qualified staff, spare parts and service, which they did very efficiently. Dealers now compete for a sale against anyone with an open door or internet access, even from outside Australia.
Have you contacted your local Member of Parliament or the Federal Minister’s Office for Small Business, explaining the current situation of our industry? Ask if you cannot emissions test it, can you sell it, ask what the service compliance intervals are, ask who will monitor them being carried out and who will monitor the obligations of sharing information – if this does not happen as a voluntary process, will the Federal Government provide a mandatory solution, as has been carried out in the USA and Europe?

Clive Townley
MOWCO