Norton's auction of the 10 machines, which date from 1898, could see them falling into private hands never to be seen again. The bikes had been on permanent loan from the famous manufacturer which had sought appropriate sites to show off its past.
The move has angered motorcycle enthusiasts. Sean Warwick, acting editor of Motorcycle News, said: 'It's extremely sad to see a once-great name reduced to plundering our national heritage. Everyone in the motorcycle industry, riders and manufacturers, will be dismayed.'
The new owners of Norton Motors 1993 - two Canadians, Nelson and Rozanda Skalbania - defended their decision. They said they were deriving no benefit from the bikes, estimated to be worth pounds 50,000.
The company, - which includes Norton, BSA, and other famous British marques - had a chequered history, struggling as the British industry collapsed under the Japanese onslaught.
The company wrote to the museums four months ago to conduct an audit of their machines. But a month ago the three museums - the Science Museum, London; the Museum of Road Transport, Coventry; and the National Motor Museum, Beaulieu, Hampshire - were contacted by Norton and told they were to lose the bikes.
The Beaulieu museum has already returned two bikes to Norton, a 1975 Commando and a 1954 250cc prototype. Five others are to follow shortly, among them a 1989 Ariel Tricycle and a 1905 Matchless, believed to be the first one made. Michael Ware, the museum's curator, said they had been offered an opportunity to buy the machines - which also include a 1940 3TW prototype, a 1949 650cc Triumph Thunderbird, and an unused Triumph T150 Trident - but declined.
He said that he had no quibble with Norton, which was entirely within its rights in requesting the return of its machines.
Barry Littlewood, the managing director of the Coventry museum, said he was sad that it was shortly to lose its 1921 Triumph model H which was loaned by the manufacturer in 1961.
'The moral implication when the machine was given to us on permanent loan in 1961 by the manufacturers was that we would keep it indefinitely,' he said.
'They had the bike and they wanted somewhere to display this part of the region's motorcycling heritage. The fear is that it will no longer be on view, and maybe not even in this country.'
Derek Robinson, of the Science Museum, was dismayed by the prospect of the loss of its 1904 21 2 hp Triumph, part of the collection since 1938, and a 1951 Sunbeam S7 in-line twin.
He said that before the bikes and two sectioned engines were handed over, he would want to satisy himself that Norton was the legal owner.
Rozanda Skalbania said the firm was being unfairly criticised over the sale by Sotheby's on 24 April. The machines had nothing to do with its plans to revive the marque with four new bikes.