IT’S the ‘i’ that’s important here. No other chainsaw on sale in the UK has it, the suffix denoting a huge shift in chainsaw technology. Stihl, in their fashion, haven’t made a huge song and dance about it, but once you pick up the 500i you know the smug buggers have done it again.

I remember trying various saws that had the then-innovative ‘scavenging engines’. Less emissions, more torque and better fuel economy, we were told. I found them uninspiring until Stihl gave me an MS 441 to test.

It had good power with lots of torque – which is what we had been promised – but it had something else, something intangible. It took an old-time cutter who worked for me to put this enigma into words. It felt familiar to him, but better in every way. It was smooth, it was well balanced and it fit. It was the last point I lingered on, realising he was right. The 441 didn’t make any promises of ergonomic improvements, but changes had to be made to accommodate the new technology and, either by luck or design, it worked beautifully.

That same cutter is still with me. He says he has one year left then that’s him done. He began felling for me about 25 years ago and he’s been a machine during that time. One constant in our time working together has been his reaction to new chainsaws. I’ve always valued his opinion when it comes to performance and handling.

He is merciless – expecting them to be as indestructible as he has been over the years – and if they can’t keep up, they don’t survive. Over the years, I have become used to hearing the same verdict: “It’s a chainsaw. It’s OK, but nothing special.”

I’ve waited years to hear something different and finally, with the 500i, which will probably be the last saw we test as a double act, I got it.

He said: “That is some saw, it really is exceptional. It has loads of power, it isn’t heavy and it’s good to use. If I wasn’t packing up, I think I would actually go out and buy one for myself.”

Well, I can retire happy, knowing that finally, after God knows how many chainsaws we’ve tested, he’s finally found one he would spend his own money on.

The question is: what is so special about Stihl’s latest professional chainsaw? I do believe, in an article written some time ago about modern chainsaws that use scavenging technology in the engine and sensor-based electronics in the engine-management systems, I said that fuel injection would be required to remove the variables inherent in a fuel system based around a carburettor. More specifically, what I said was that electronic fine-tuning that gave the same feel as an old manually tuned piston port engine would never be possible without fuel injection. It means the same thing – you get a new saw that feels like an old saw that’s been tuned by an expert.

Here is that saw, the Stihl MS 500i.

It’s truly a new beginning. The saw is remarkably simple to use, with no on/off switch, no choke, no fiddly start procedure and no fluffy running, no wandering tickover and lots and lots of instant, smooth power.

Forestry Journal:

Firstly, Stihl have shown a wee sleight of hand. The 500i will naturally be pitched against the MS462 and Husqvarna’s 572 XP, but they both give up a little in capacity. The 500 is as near as spit to 80 cc and that is a big saw for everyday chainsaw work, but whether it’s a weight benefit from the lack of a carburettor or a weight-saving plan well executed, it doesn’t feel like a bigger saw than the other two. It is better looking than the Husqvarna, if not as pretty as the 462, though that doesn’t matter to chainsaw operators. I’d like to think its quirky style has been created through necessity to accommodate the air cleaner attached to the throttle body. It must have been a change for the designers to finally have something else to work on that wasn’t a carburettor inlet.

Looking around the rest of the saw, it is all pretty straight-forward. It’s when we get to the back and start looking for the on/off switch and the choke lever that things really begin to change; there is no choke and there’s no on/off switch. But there is a primer button. I have railed against primer buttons for many years. I have never used them on the professional saws they are fitted to and I’ve never really understood why they were there. It’s a general rule of thumb that you don’t need a primer button with a choke flap fitted in the carburettor unless it’s on an amateur saw and the user needs all the help they can get to start it.

So, in an attempt to reconcile myself with the stop button and primer bulb lurking where the choke and on/off lever would be on a conventional Stihl, I needed to do some research about fuel injection.

I’ve looked at all sorts of fuel injection systems, including the magnificent two-stroke Detroit diesel once fitted in many American trucks and one very memorable Timberjack skidder the FC ran out of Dalby workshops many years ago. It’s a two-stroke with diesel fuel, exhaust and inlet valves opened and closed by a single camshaft that also operates mechanical fuel injectors.

Each injector is a little self-contained pump that squirts a dollop of fuel into the cylinder at the right moment.

There’s no injector pump. It’s all done right there in the cam cover with a low-pressure fuel supply to each injector. The whole thing makes an unholy racket and produces prodigious torque once it’s spinning at peak rpm. It also produces enough pollutants to give the green lobby a fit by the time it gets to the end of the street.

The Detroit doesn’t need much in the way of head pressure to the injectors. Most injection systems need some kind of pressure to get the ball rolling, though with common-rail diesels it’s a whole other story we won’t get into here.

The reason for the primer bubble is to provide a slightly pressurised head of fuel in the system right through to the fuel tank return. In most fuel-injected engines, and on motorbikes in particular, you will hear an annoying buzzing when the ignition is switched on. This is the fuel primer pump providing head pressure for the fuel-injection system. It isn’t practical to put a priming pump and battery into a chainsaw (not yet, at least), so it’s down to the operator and the primer bubble on the 500i is there for that very good reason.

That covers almost all the technical stuff, except for the remarkable power output of 6.8 bhp (5 kW), up from the 462’s substantial 5.9 bhp (4.4 kW) and its power-to-weight ratio of 1.2 kg/kW against the 462’s 1.4 kg/kW and the thing you can’t measure, which is sheer feel.
The 500i is light for such a powerful saw. It weighs 6.2 kg compared to the 6 kg 462 (both powerhead only, with no fuel or oil) and that despite it being almost 10 per cent bigger at 79.2 cc, compared to the 462’s 72.2 cc. In practice, the 462 and 500i feel almost identical to use, apart from the 500i feeling more powerful and having notably rapid acceleration.

Forestry Journal:

These are the things you notice most about the 500i. Once you get past pumping the primer bubble a few times and tugging on the starter, the reward is instant. There’s no uncertain fuelling here. It revs clean and crisp right from the start. Good practice is to warm any saw through before starting work and, given any new saw in this class is going to cost around £1,000, it’s essential to give them a minute to warm through.

The 500i revs like nothing else out there at the moment. Compared to the old 66 cc saws we used back in the day, it’s almost unimaginable how pedestrian it makes them feel. It accelerates in an instant, with the quickest pickup I can think of on any production saw I’ve tested, and it is a pleasure to use. It makes cutting dry ash less of a task, and the added benefit is that we fell and dress out big trees with one saw.

I ran the test saw on a 20” bar which is what we use as standard for hardwood felling. I have tried it with a 25” bar fitted and it comes in handy for the bigger trees in the stand, but it’s less handy when there’s a lot of big branches to remove. The 500i doesn’t feel out of balance with the longer bar and it certainly has no problems turning it. You can bury the whole bar in a big tree and it doesn’t back off, testament to the fuelling and the design in general. This really is one exceptional saw that marks the beginning of a new chapter in professional chainsaws.