The paper presents the results of the introductory investigations of the correlation between the fluctuation of the indicated work and the fluctuation of the crankshaft speed and the electric current from a generating set. A clear relationship between the engine indicated work and the electric energy calculated in the time interval angularly shifted regarding the beginning of the engine cycle was stated in the case of the single-cylinder generating set. The indicated work of the consecutive cycles also well correlates with the crankshaft angular acceleration in the determined cycle phase point. A little worse is the correlation between amplitude of electric current and indicated work. The correlation between electric energy calculated in 90 degree angle interval and indicated work was also stated.