The first Sisu's were powered by Volvo supplied Penta engines. The 1934 presented Sisu SO-models were equipped with Finnish produced Olympia engines which turned out to be too weak and unreliable. Therefore, the power source was changed again already in 1935 launched SH-series which was powered by American Hercules engines. In 1937 Sisu became available with Hercules diesel engine but they were not sold many yet. In the following year another American engine, Buda was added in the selection - this Sisu-series was called SB respectively.