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GP Week : Issue 121
Moto GP FEATURE >> Even for its time, the Manx was an old-fashioned engine. Its strength lay in extreme refinement of the two-valve squish cylinder head and camshaft design: it was robust, well-cooled, and accurately designed and made. At the start of the GP era, it was a long-stroke thumper – 79 x 100mm bore and stroke; the “short-stroke” (so-called) came in 1952, at 86.1 x 85.6 . With dour Ulsterman ‘Professor’ Joe Craig at the helm, the engine was continually refined. The final version of 1962 produced some 50 horsepower at 7,200 rpm. This is the number that coincides with Moto3. The one that coincides least is the weight. The Norton scales in at more than 130 kg. The Moto3 runs to a minimum weight of 148 kg – that’s the bike and the rider. Honda’s item has a kerb weight of 84 kg. Specification-wise, we are in two different eras. The Honda’s version of “short-stroke” is a lot more extreme than Norton’s. The 250cc four-stroke’s dimensions are 78.0 x 52.2. In percentage terms, the stroke is 66.9 percent of the bore: Norton’s “short-stroke” was all but square, at 99.4 percent. The Honda has two overhead cams like the Norton, but where the old-timer used a vertical shaft with bevel drive, the Honda has a chain. And where the Norton had finger cam followers, the Honda has inverted buckets. They’re still a pair of single-cylinder racing bikes, with about 50 horsepower. Where any similarity really ends is when they start up. A Norton with a megaphone exhaust has an ear-splitting bark and a flame - spitting over-run. The Honda, as demonstrated at Catalunya, has a purring exhaust note barely louder than that of the roller-starter engine. Fifty years of development means we require only half the cylinder capacity to make equivalent horsepower, and half the fuel. The Honda’s tank holds 11 litres; Manx riders used to stretch out over black-lined silver tanks holding 25 litres. That’s progress. But only of a sort. Few have summed up the Manx Norton, and its differences with its modern successors, better than former rider and GP winner Ken Kavanagh, in his foreword to The Manx Norton by Mick Walker (Redline Books): “Maintenance was almost nil: check the tappet clearances, adjust the chains, blow up the tyres. A whole European season could be done on three sets of valve springs, two spare valves and one big-end – maybe no more than fifty quid – and the whole thing could be overhauled in anybody’s back yard with a few spanners. This was the true spirit of racing machines for perennially poor riders, not the expensive junk the makers foist off on today ’s boys, obliging them to fall under the grasp of sponsors.” Moto3 and Manx Norton (right) – deja vu? 33