Bikesales Staff•23 Oct 2011

NEWS

Stroke of genius

What happens if you shoe-horn a hotted-up 500cc V-four two-stroke into a tricked-out YZF-R6 chassis? You get a YRZ500, that's what

Robert Hook is an artist by profession. Or more accurately, he’s a large-scale metal sculptor. Hook turns creative concepts for fellow artists into full-size fabricated reality in his Brunswick workshop in inner Melbourne.

Hidden among the jigs, cutting tools and welding equipment in the converted warehouse is one work of art that wasn’t commissioned by a paying customer, and is unlikely to ever be sold, but is a perfect example of Hook’s craft – his amazing YRZ500.

What’s a YRZ500, you ask? Take a 1984 Yamaha RZ500 V4 two-stroke, marry it with a 2006 Yamaha YZF-R6, and you’ve got a YRZ500.

“I bought an RZ500 in 1988, and rode it for the next 10 years. When I parked it in 1998 it had 140,000km on the clock,” says Hook. “Ten years on I decided it was time to either restore it, or turn it into a track day bike, so I started looking for parts.

“That’s when I came across a 1985 model RZ500 at Motorcycle Import Centre in Brisbane. It was the limited-run Japan-only model with alloy frame, alloy shock body, alloy ’bars – and for $8000 I couldn’t say no.

“I wanted a track day bike, and I now had two RZ500s, so I thought ‘why not’? But rather than convert one of the RZs for track use I thought it would be fun to take the RZ engine and put it in a modern chassis – and the YRZ500 is the result.”

Hook makes it sound easy, but taking a 1984 V-four two-stroke and fitting it into a 2006 four-stroke chassis is no mean feat – especially when the end result looks like it could have rolled straight out of the factory door.

He opted for his ’84 RZ as the donor bike, as the engine on that needed a full rebuild anyway.

“I kept the RZ engine and the electrics, and sold everything else on eBay,” says Hook. “And then I found the ideal chassis at Vic Wreckers – a 2006 R6 with less than 5000km and no impact damage. The rolling chassis cost me $4200.”

Hook now had the major components to get his project underway, but he still had to marry the strange bed partners together. And he still had to source a load of ancillary parts for a bike that had no guidebook or parts manual to follow.

“I’d done no research beforehand – it just seemed like a good idea at the time,” recounts Hook. “Most importantly I wanted to ensure the countershaft sprocket was in the right place, so Don Stafford (of Melbourne dealership Stafford Motorcycles) let me pull the cover off an R6 in his shop and measure things up. Once I had that measurement locked in I could start.

“The main thing was to make sure the RZ engine fitted in the right place in the R6 chassis. I have to admit to being surprised how everything fitted so well.”

Hook had to do some minor trimming of one of the engine covers, and he had to remove the RZ’s kickstart, but other than fabricating some new engine mounting brackets it was pretty much a bolt-in affair. The standard RZ500 carburettors wouldn’t fit either, but Hook had some exotic plans for the intake system.

The sub-frame, rear-sets and foot-pegs were all knocked up in-house by Hook too.

“Losing the kickstart isn’t a major hassle, as the bike is for track use. It would be a bit different if it was for road use – bump-starting at traffic lights or in car parks might get some strange looks!”

The crankshaft, gearbox and clutch all remain as standard RZ500, with the crank lovingly rebuilt by Don Stafford.

“I owe Don huge thanks for his enthusiasm and time. He’s been a keen supporter of the project from day one.

“For the top-end I used Yamaha’s own tech specs for modifying the pistons, port height, and heads – as well as the pipe specs. The barrels are rebored to maximum Yamaha oversize, they’ve been ported and the squish has been altered to suit. I’ve got 110 horses at the rear wheel.”

Those ponies come courtesy of a set of 28mm Mikuni flatslide carbs sourced from the US, along with Boyesen reed-valves. The carbs currently run open mouths, but Hook is working on a custom airbox.

“You could say it’s quite a work of art – there’s quite a bit of sculpting involved,” grins Hook.

Like the carbs and reeds, Hook sourced a lot of the components via the web. The handlebars came from Red Racing in Italy, as did the Extremetech steering damper (www.redracingparts.com). Hook got his titanium bolts and other fastenings from Pro-Bolt in the UK (www.tastynuts.com), as well as some through Red Racing.

“I got the discs from Hong Kong off eBay, although the Galespeed forged wheels were sourced locally – via Sportsbike (www.sportsbike.com.au),” says Hook. “They were $3000 for the pair. They’re the usual 3.50 front and 5.50 rear, as on the R6.”

Everywhere you look there are neat touches, like the Carbotech brakelines, Jolymoto mufflers and Gibson pipes.

“The pipes are similar to TZ250D/E pipes, and fit amazingly well seeing the chassis was designed for a four-into-one, not four separate expansion chambers. Pete (Gibson) did a top job.”

Okay, it looks the business, but what’s it like to ride?

“When I first started it, it sounded just like a GP bike with that ‘brrrap, brrrap’ from the pipes,” enthuses Hook. “It sounds great. It hasn’t got the instant throttle response of a GP bike, as it’s still got the balance shaft, standard crank and wet clutch. But for a production engine it’s close.

“It’s really neutral too. Static weight distribution is 52 per cent front and 48 rear, so it’s right in the ballpark. And it weighs only 140kg, so with 110 at the rear wheel it’s got some go. I couldn’t be happier with how it’s come together – and it’s so much fun.”

Well, Hook could in fact be a little happier. First time out while sorting the carbs he seized it – thankfully with only a minor nip-up that did no damage.

With that teething hiccup now sorted, watch out for a brrrap, brrrap ‘R6’ with four stubby mufflers at a ride-day near you. And if you want to find the owner, just look for the biggest grin in the pits. Chances are it will belong to the owner of this spectacular YRZ500.

HOOK, LINE AND SCULPTOR

For a man whose day job is large-scale sculptor, Robert Hook has an impressive CV when it comes to riding, building and fettling motorcycles.

Hook raced a Yamaha TZ350 and Honda CB750F in New Zealand in the early ’80s before deciding he needed a change of scenery, with Australia providing that opportunity.

When Hook first arrived in Australia he worked with top-rated national GP competitor Hamish McNicol and his 1988 Honda RS250. From there it was a stint with Marty Craggill on the Malcolm Campbell-run OKI Honda RS250 in 1991, and then with Andrew ‘Smiley’ Thompson on the same bike in 1992.

Craggill would go on to win two Australian Superbike Championships riding for Team Kawasaki Australia in 1997 and 1998.

Hook then worked with Shannon Johnson in junior motocross in 1995, and with him again in 1998 when Johnson went road racing. Johnson would go on to win an Australian Supersport Championship in 2002.

Along the way Hook spent time with master craftsman Bruce Woodley at performance and restoration specialist Powerflow, so there can be no doubting Hook’s CV when it comes to bikes.

At 52 years of age Hook is proof that you’re never too old to stop having fun. His home-grown YRZ500 is proof of that.

FROM YZR500 to RZ500

In 1975 Giacomo Agostini became the first person to win the World 500GP Championship on a two-stroke. The bike was Yamaha’s four-cylinder 500.

Kenny Roberts then brought Yamaha three more 500GP titles from 1978-1980, before losing out to the factory Suzuki RG500s of Marco Lucchinelli and Franco Uncini in ’81 and ’82 respectively.

By 1983 Roberts had eventual champion Freddie Spencer and Honda’s nimble RS500 triple to contend with as well, although Roberts’ V4 YZR500 still held a distinct power advantage.

Imagine the impact in 1984 when Yamaha introduced a descendant of that 1983 Roberts factory GP bike for the man in the street. It was called the RZ500.

It had a 500cc V-four engine, like Roberts’ bike, and it had liquid-cooling and twin crankshafts, like the GP bike. At the time it was the closest thing to a 500GP bike that Joe Average could buy.

Three versions of the RZ500 were available worldwide. The RZ500 for Australia, New Zealand and Canada (pictured right) came with Yokohama OEM tyres, while its mechanically-identical European counterpart was known as the RD500LC, and sported Michelin tyres and a different paint scheme.

A third version (RZV500R) was produced for Japan, and scored a lighter hand-welded aluminium frame instead of steel, items such as braided brake-lines and aluminium footrest brackets and rear shock body, but also a de-tuned engine (30 per cent less power) for the domestic market. Emission restrictions meant the RZ500 was never sold in the US.

Roberts’ 1983 works GP bike used a 50-degree, twin-crank V-four engine, and so too did the RZ500 road bike. Both engines were equipped with Yamaha’s YPVS exhaust power valves, and both had removable cassette-style six-speed gearboxes. However, whereas the Roberts’ OW-70 had rotary disc induction, the RZ500 scored reed valves.

The road-going RZ500 produced around 84hp (61.8kW), with torque building from 6000rpm to a peak at 8500rpm.

The RZ500 chassis was innovative too, with the rear shock located horizontally under the engine to allow room for the exhausts, YPVS valves and intake paraphernalia. Other ‘innovations’ included adjustable anti-dive valves for the front fork and a 16in front wheel that was arguably out of place on such a short-wheelbase motorcycle.

The RZ500’s greatest achievement in Australia was when Michael Dowson and Richard Scott rode one to victory in the 1984 Castrol 6-hour race at Oran Park, holding off the more powerful Honda VF1000R of Wayne Gardner and John Pace in the final laps. It was a true David and Goliath battle, with David winning one of the all-time classic 6-hour encounters.

Story courtesy of Motorcycle Trader.

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Stroke of genius

HOOK, LINE AND SCULPTOR

FROM YZR500 to RZ500

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