FROG 100 - version 2 (early 1948)

The FROG 100 bicycle spoke long stroke diesel engine marked FROGs initial venture into the commercial production of diesel engines. This engine became a steep learning experience for FROG leading to three significantly updated versions within its first year of production to deal with the increased stress forces produced by a diesel engine design.

The original version of the FROG 100 was launched in late 1947 with the design being undertaken George Court. Notably this version featured cylinder cooling fins machined as part of its Meehanite cast iron cylinder. It is worth mentioning that the engines piston was also machined from Meehanite an unsuitable material combination for a piston and liner.

The second version of the FROG 100 was introduced in mid-1948 with design modifications believed to have been carried out by Bert Judge. The integral cylinder cooling fins were replaced with a 13-fin aluminium cast cooling jacket while the new finless cylinder was machined from steel and case hardened. Notably the pictured FROG 100 version II bares the serial number 2897.

The third and final version of the FROG 100 bicycle spoke diesel engine was unveiled in late 1948 with the most significant change being the adoption of a new eleven-fin cast aluminium cylinder cooling jacket giving both enhanced strength and extra rigidity to the engine.

Capacity 1 cc in (0.061 cu in) - Bore 0.375 in (9.52 mm) - Stroke 0.55 in (13.97 mm) - Power 0.071 BHP 8000 RPM (0.053 KW) - Weight 3.75 oz (106 g) - Induction Front rotary valve - Ignition Diesel (Compression ignition) - Piston Liner Cast iron piston Cast iron Cylinder