A seismic change in British motorcycle design happened in 1957: the introduction of ‘unit’ construction combining the engine, primary drive and gearbox in one case.
The first Triumph twin to have unit construction was a 350cc Twenty One 3TA (the 21 referred to the engine size in cubic inches for the US market).
These days it seems pretty obvious but since the dawn of the first motorcycles, most had what we now call ‘pre-unit’. That is, the engine was one item, the primary drive was by chain in its own oil-filled primary chaincase, and the gearbox was separate. It worked but with plenty of space for grime and grease to build up, not mention awkward places to drop a nut or spanner.
The idea wasn’t completely new. Triumph had already deployed unit construction on its 149cc single-cylinder terrier and the following 196cc Tiger Cub in the early 1950s. But it was part of Triumph boss Edward Turner’s plan to modernise the essentially pre-war motorcycles.
That first T21 was clothed in what became known as the ‘bathtub’ bodywork to further emphasise its clean looks. It was a steel pressing which wrapped around the rear half of the bike in one flowing piece right to the end of the mudguard. The front mudguard was also bigger to reduce road spray soaking the rest of the bike. Wheel sizes were reduced to 17 inches to reduce the seat height and give it an all-round appeal.
The 350 was followed by a 500cc twin, equipped very similarly, and in 1963, the 650cc bigger twins also changed to unit construction. BSA quickly followed suit but not Norton or Velocette, who held onto seperate items until into the 1970s.
1957 Triumph 350cc Twenty-One
First unit Triumph twin at Mecum auction
Coming up for auction in the world-famous Mecum Monterey auction is the very first unit construction Triumph. Yes, serial number H1, constructed especially for the motorcycle’s launch at the RAI Motorcycle Show in The Netherlands in February 1957. After the show it went to a Dutch dealer and it was sold and registered on April 5, 1957.
More than 65 years later, Triumph’s very first Twenty-One, the first unit-construction parallel-twin motorcycle to leave the Meriden factory, is set to cross the auction block, complete with its historically significant H1 serial number.
The auctioneer said, “Purchased by its current owner from a neighbour in the Netherlands, the Twenty-One was complete and came with extensive service records, which are included with the motorcycle. It was dismantled for restoration and then brought back to Texas in 2015, where well-respected but low-profile restorer Kevin Giles completed the renovation.
“This Twenty-One is impeccably detailed with a comprehensive engine rebuild and repaint in the correct color, and it’s being sold with its original Dutch registration certificate.”
The historical significance means that this Triumph 3TA is estimated to sell for somewhere between $30,000 and $40,000.
