The Panther Model 100 was a British motorcycle. It had a 598cc, 6.5:1 compression ratio, 87 x 100 mm, ohv sloper engine in a frame where the engine replaces the front down-tube. Panthers were manufactured in Cleckheaton, Yorkshire, UK from 1900 to 1967. Launched in 1932, the Model 100 continued through to 1963. While the engine and overall layout stayed essentially the same, the specifications steadily evolved over these thirty or so years.
A 598cc engine was used in the Model 85 Redwing (previously Model 80) from 1929 to 1930 and the Model 60 (previously Model 3) from 1928 to 1935. The Model 100 engine was largely a development from the Model 60. The earlier engines had compression ratios of either 5.4:1 (Model 60 pre-1930) or 7.0:1 (Model 85 and Model 60 post-1929). The frame derives from the 1928 Panther and the tank from the 1932 Model 50. The history of the development of the Model 100 is as follows.
1932 - Model 100 launched. P&M 4-speed gearbox, Webb forks.
1933 - Sturmey-Archer 4-speed, hand-change gearbox introduced. Frame redesigned. Terry de luxe saddle.
1935 - Panther M100 Motorcycle 1935 - Deeply finned sump and improved lubrication. This new bottom end remained almost unchanged for the next thirty years. This machine had a 6.5:1 compression ratio, 87 x 100 mm, ohv sloper engine. The 1935 Model 100 was the machine on which Miss Florence Blenkiron and Miss Teresa Wallach undertook the epic journey from London to Cape Town, crossing the Sahara: the first such journey on a motorcycle combination. 
1937 - New fully chromed fuel tank with red and black lined cream panels and snarling Panther logo. This was the last year of the "Redwing" Model 100