Market Report: Power Tools

Damage limitation

Phil Mist tests Husqvarna’s OilGuard system, developed for its K750 disc cutter and designed to eliminate the risk of damage caused by incorrect fuelling.

It is a simple fact that all disc cutters have two-cycle engines. There is, of course, nothing intrinsically wrong with such power units, being every bit as efficient in many ways as four-cycle engines. They rev well, and have an excellent power to weight ratio. However, the apparently simple task of having to mix petrol and oil in the correct ratio can be a step too far for many untrained construction workers. Virtually everyone in the tool and equipment hire industry knows of instances where two-cycle equipment has been returned with either pure petrol or, worst of all, diesel, in the fuel tank. The consequent damage can be severe and is expensive to repair. Also, whilst the absence of oil in the fuel is obviously damaging, so is an incorrect mixture. Too much oil and the engine will falter, too little and the engine will usually overheat or, even, fail, especially when under heavy load.

In an attempt to eliminate such problems, Husqvarna has introduced the OilGuard system, available as an option on its popular K750 300mm-diameter disc cutter. Incorporating a special optical sensor,
it is designed to ensure that the machine will run at full throttle only when fuelled with the correct oil and petrol mixture, and then only if the special OilGuard lubricant, available from the manufacturer,
is used. Whilst a significant number of two-cycle outboard engines have for many years been equipped with an oil injection system to prevent their use if only pure petrol is in their fuel tanks, there has been no such development in the disc cutter market. Even OilGuard cannot stop operators putting an incorrect mixture into the tank. However, it does prevent the engine from revving at full throttle if no oil is present in the fuel.

A blue box inside the engine of an OilGuard machine incorporates a light emitting diode (LED), which monitors the colour of the fuel fed to the engine. A yellow dye in the lubricant acts as a colour filter, blocking blue light and, in turn, preventing a photo-transistor from activating an electronic circuit breaker. If the system does not detect the pigment, then the circuit breaker connects to ground and limits the engine speed to only 3,800 rpm.

When filled with pure petrol, the test machine happily revved for a few seconds but then slowed down just as the manufacturer claims. Despite my best efforts, I could not get the machine to rev again until I had added the proper oil to the fuel. I then tried mixing non-OilGuard lubricant in the correct ratio with petrol, with similar results: plenty of revs to begin with, soon to be replaced by an idle-only speed. Finally, with both the correct fuel/oil mix and OilGuard oil, the machine worked perfectly.

Husqvarna claims that, even if pure fuel is used, there is little likelihood of engine damage because the OilGuard system cuts in before major problems can occur through lack of oil.

In certain circumstances, the OilGuard equipped system can be overridden, by replacing the blue activation plug, which is positioned by the stop switch, with an orange ‘blind’ plug. However, this should only be carried out by a qualified fitter, and if the engine is damaged as a result, it could result in the invalidation of the manufacturer’s product warranty. This alteration should obviously only be done if the special oil is for some reason temporarily unobtainable, and afterwards the machine can only be re-set for normal OilGuard operation by an authorised service agent. •

T 0870 850 1394
W www.husqvarnacp.com

Executive Hire News › Archives › July 2008 › Market Report › Damage limitation

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