With an experienced team and a lot of data.
Protect your 1968 BSA D13 Bantam from the unexpected.
In the 1930s, DKW was pretty much the largest motorcycle manufacturer in the world, but the DKW model that holds the record for the largest production run ever (after the Honda Cub), was actually built by at least eight other manufacturers in six different countries.
DKW actually stands for Dampf Kraft Wagen (Steam Powered Engine), though most think of Das Kleine Wunder (the Little Wonder). The company pioneered Schnurle two-stroke loop scavenging in the 1930s, eliminating a deflector piston and improving combustion efficiency. They also developed efficient transfer ports. Adler and TWN would go on to copy the design.
The DKW RT 125 first came about in 1939 and was embraced by the Wehrmacht, as the Nazis had invasion plans that valued swift personal transport. It was built in large numbers during the war, but even more were built after the hostilities ended. Curiously, the bike even served on both sides of the war, as Britain’s Royal Enfield copied it as the 125 cc “Flying Flea” for allied paratroopers.
DKW’s patent on the bike was voided in 1945, and it went on to be built in Britain by BSA as the Bantam from 1948-70, in the United States by Harley-Davidson as the Hummer from 1948-66, in Poland as the Sokol from 1947-50 and as the SHL M04 from 1948-52, as the Triumph 125 (the German company) in Holland, and the Moskva M1-A and IFA from 1946-66 by the Soviets. Yamaha in Japan also reverse-engineered a German example in the 1950s and designed the the YA-1 (Red Dragonfly). DKW even kept on building the bike themselves in Ingolstad from 1949-57.
The BSA Bantam had sprung front forks and a hard-tail until 1948, when a plunger rear end was also offered. The original 125 cc D1 was built until 1963. It made 4 hp and had a three-speed transmission, with a top speed of 54 mph. By the time Bantam production ended in 1970 when it was known as the D14, its 14 bhp engine displaced 175 cc, the frame had a swing-arm rear suspension and top speed had risen to 75 mph. The Royal Mail used BSA Bantam D1s for telegram delivery into the 1960s, and the job was a testament to their toughness, as the riders were mostly teenagers.
BSA Bantams are inexpensive and easy first collector bikes. They weigh only 178 lbs, and the seat is low. Bantams and their siblings can be relatively trouble-free as far as old British bikes are concerned, but the electrics can be feeble and the points will need frequent checking. Even a somewhat scruffy one will be easy to restore and parts availability is quite good, but finding a good, complete, running example isn’t difficult.