Yamaha’s polar packhorse is snow joke
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By Dave Abrahams
Just before Christmas we got a call from Yamaha technical genius David Freeman, a former Grand Prix technician who is now Yamaha Motor Europe’s roving fix-it guy.
“Have you ever,” he asked, “been up close and personal with a snowmobile?”
Since I live in sunny Sarf Effrica, the answer, of course, was no.
“Right,” he said. “Get yourself down to Helderberg Yamaha pronto; we’ve sold a dozen of them to the South African National Antarctic Expedition and they’re helping us prepare them for delivery to the base this summer.”
So there I was, in 30-degree heat, getting a sneak preview of what the well-dressed polar scientist is riding this season. Unfortunately, due to lack of snow, I didn’t get a chance to ride one.
I tried to persuade Yamaha that I really needed to go down to Sanae for a test ride, but they weren’t biting.
Nevertheless, Freeman’s guided tour blew away just about every pre-conceived notion I’d had about riding on snow. To start with, all the warning labels and manuals were in Russian.
Yes, Cyril, the VK540 IV utility snowmobile is made in Japan, but it’s one of the very few two-stroke snowmobiles still in production and Russia is almost the only place where they’re still legal. But four-stroke snowmobiles, while great for racing on hard-packed snow trails, are at once too heavy and too unreliable for the extreme conditions faced by workhorse vehicles in polar regions.
Despite (or possibly because of) their primitive operating system two-stroke engines have proved to be far more reliable when the chips are down, and there is a strong groundswell of pressure in Canada and Alaska from operators whose snowmobiles have to work for a living to find a way around the clean air regulations so that reliable two-stroke utility snowmobiles can legally be imported again.
The next surprise was that that Freeman’s most important job was disconnect the autolube system on the Sanae snowmobiles - but not because of the extreme conditions they will face. Apparently the highly-qualified, technology-savvy scientists who will ride them cannot be relied on to check the oil level in the autolube tank, so when they book out a can of fuel, the vital two-stroke oil is already premixed.
One thing polar explorers have found is that the simpler a machine is, the more reliable it will be. The VK540 has a straightforward 535cc Yamaha piston-port parallel twin with reed-valve inlets and just one 38mm Mikuni side-draught carburettor, for a grand total of eight moving parts.
Compression ratio is 6.5:1, power output is ‘sufficient’ at 6500rpm and peak torque ‘adequate’ at 6000. Cooling is by air (no coolant to freeze, no pump to fail) using a big belt-driven fan to pressurise a still-air box on the exhaust side of the barrels with (very) cold air.
It drives a 508mm-wide plastic belt with 35mm ‘treads’ via a constantly variable belt drive and a three-speed – high, low and reverse – transfer case with a mechanical disc brake (operated from the left handlebar grip) acting on the output shaft.
And that, apart from two 228mm-wide skis in front with trailing-link suspension that looks suspiciously similar to that of a Cessna 172 nosewheel circa 1967, is that.
It’s all built on - or in - a box made out of ordinary mild-steel sheet and extruded aluminium sections, with two independent sets of torsion-spring suspension (one behind the other) under the belt, modulated by very ordinary motorcycle dampers, a basketlike load bed behind the long, deeply padded dual seat and a cavernous storage compartment under it.
KEEP IT SIMPLE, STUPID
There’s only one gauge – a speedometer that reads to 160km/h. Even the fuel and oil level displays (the latter redundant on the Sanae machines) are merely clear plastic tubes attached to the relative containers at top and bottom and reflecting the level inside by simple gravity.
About the only concessions to modernity are the heatable handlebar grips and thumb throttle - but that’s just so you can ride it wearing gloves thin enough to feel what you’re doing.
Makes you wonder, doesn’t it, why we insist on constantly increasing the complexity of the vehicles we drive every day when truly extreme circumstances consistently demonstrate the accuracy of the oft-quoted ‘Kiss’ principle: "Keep it simple, stupid”.
YAMAHA VK540 IV SNOWMOBILE SPECIFICATIONS
Engine:535cc fan-cooled two-stroke parallel twin.
Bore x stroke:73 x 64mm.
Valvegear: Piston port with inlet reed valves.
Induction:38mm Mikuni side-draught carburettor, premix fuel.
Ignition: Digital TCI.
Clutch: Automatic centrifugal dry clutch.
Transmission: Variable-ratio belt drive with high, low and reverse ranges.
Front Suspension: Trailing-link telescopic struts with gas-charged hydraulic dampers.
Rear Suspension: Torsion springs with flip-up rails and gas-charged hydraulic dampers adjustable for preload.
Brakes: Mechanical disc on transmission output shaft.
Front skis:228mm blow-moulded plastic with integral split keel
Front stance:960mm centre to centre
Rear track:508 x 35mm Ripsaw Full Block moulded plastic.
Fuel tank:31 litres.
Thanks to: Helderberg Yamaha, Cape Town.