1971: the start of the two-stroke GP motorcycle revolution: Mat Oxley

Grand prix motorcycle racing reached an important crossroads 50 years ago. Imagine that Jackie Stewart’s closest rivals during the 1971 F1 World Championship were a bunch of young upstarts driving pimped-up Jaguar E-types and Ford Capris.

This was the situation in which Giacomo Agostini found himself that summer. During 1971 the Italian stallion won his sixth consecutive 500cc world title, riding four-stroke grand prix bikes belonging to the Agusta family. He had no serious opposition because Meccanica Verghera Agusta was the only manufacturer contesting the championship, but the privateers who shared the podium that year rode mongrels powered by two-stroke engines taken from a new generation of high-performance Japanese road bikes.

Agostini’s state-of-the-art three-cylinder MV made around 80bhp and was available only to those riders anointed by Count Agusta, which in 1971 was Ago and no one else.

Suzuki’s T500 two-stroke twin and Kawasaki’s H1 two-stroke triple road bikes were available to anyone who could afford them and the engines could be tuned to make around 70bhp. A T500 or H1 road bike cost £900 (£13,000 now), so these machines were a godsend to the lower ranks who didn’t have grand old patrons signing the cheques.

The two-stroke – with its ear-splitting chainsaw yowl and double the power strokes of a four-stroke – had conquered the smaller grand prix classes. By the dawn of the 1970s, the premier 500cc category was the only class yet to be overrun by the ‘stink-wheels’.

Older members of the racing establishment were convinced that the citadel would never be breached by the two-strokes, but they were about to be proved wrong.

In 1971 Suzuki sent several XR05s – tuned T500 engines in rudimentary race chassis – to Europe. Initial development of the XR05 had been undertaken in the US, where the bike was up against Triumphs and side-valve Harleys. An early problem was the air-cooled engine’s 900rpm-wide powerband, which required riders to slip the clutch at every gear change, with inevitable consequences.

The XR05 had a belt-and-braces lubrication system, with oil mixed in the fuel augmented by an oil-pump actuated by a handlebar lever, because two-strokes run hot (all that extra power doesn’t come for free) and can devour pistons and crankshafts.

Suzuki’s first XR05s were so likely to self-destruct that contracted rider Dick Hammer qualified for the 1968 Daytona 200 on one, then switched to a Triumph for the race. He considered the XR05 too dangerous to risk over full-race distance. Suzuki sacked him.

The company made the breakthrough the following year when Art ‘The Dart’ Baumann rode an XR05 to victory at Sears Point, the first US championship success by a two-stroke.

“Ago knew he had to go two-stroke, so he joined  Yamaha in 1974”

All that know-how went into Suzuki’s 1971 grand prix XR05, which by midseason was fast enough to make Agostini sweat for his victory laurels. Australian Jack Findlay made history when he rode his XR05 to win the Ulster GP, the first premier-class success by a two-stroke. It should be noted that Findlay won the race in Ago’s absence. MV didn’t travel to Dundrod because The Troubles were at a deadly stage. However, the citadel had finally been breached. Over the next five years four-strokes would disappear from grand prix grids as two-strokes became faster and less fallible.

Just weeks after Suzuki’s victory Kawasaki won its first 500cc grand prix with a racing version of its H1, when Briton Dave Simmonds won the Spanish GP at Jarama. The H1 road bike was such a wild thing that motorcyclists nicknamed it ‘the widow maker’. Inevitably the race bike wasn’t much nicer.

At Daytona that year H1-R rider Yvon Duhamel complained of a nasty speed wobble on the banking. When mechanics checked the bike they discovered that all the front wheel spokes were loose, but when they went to re-tighten the spokes they were tight. Kawasaki had made the wheel hubs in magnesium with a cast-in liner. The heat generated by the brake caused the magnesium to expand.

Despite their deficiencies the XR05 and H1-R were the only machines that got close to Agostini in 1971. The hybrid road/race bikes filled second to sixth positions in the standings.

Two years later Yamaha launched the first fully prototype two-stroke 500 GP bike, the water-cooled four-cylinder 0W20. Yamaha tried to tempt Agostini away from MV but the two-strokes were still too fragile for his liking.

Instead Finn Jarno Saarinen rode the 0W20. Saarinen won the first grand prix of 1973, his speed aboard Yamaha’s 100bhp weapon causing Ago to crash in his efforts to keep up. Saarinen won the second race too but lost his life at round three when he was involved in a pile-up after a two-stroke engine seizure.

Nevertheless, Ago knew he had to go two-stroke, so he joined Yamaha in 1974, relying on factory staff to keep him safe. Mechanics hand-prepared every piston, crosshatching them with emery paper to improve lubrication.

In August 1975 Agostini secured the 500cc world crown aboard his 0W26, the first premier-class championship success by a two-stroke. They reigned supreme for the next quarter of a century, until grand prix rules were rewritten in 2002, allowing 990cc four-strokes to race the 500cc two-strokes.

Mat Oxley has covered motorcycle racing for many years – and also has the distinction of being an Isle of Man TT winner 

Follow Mat on Twitter @matoxley