The prototype was refitted with BMW VIz 500 engines, larger radiators, and wooden fixed-pitch propellers of TsAGI design. Single-wheel landing gear was deemed too weak and was replaced by tandem bogies with tires. The first pre-production TB-3 4M-17 flew on 4 January 1932 with and I. F. Petrov at the controls. Unexpectedly, subsequent mass-produced aircraft were found to be 10–12% heavier than the prototype, which significantly hampered performance. The discrepancy was discovered to be due to high positive tolerances on raw materials which resulted in steel sheetmetal, pipes, and wires being much thicker than on the carefully constructed prototypes. The aircraft were also more crudely painted with a thick layer of camouflage and lacquer. The factories asked the workers for suggestions on reducing the weight, paying 100 roubles for each removed from the aircraft. In combination with OKB efforts, this resulted in weight savings of almost . Despite this, production aircraft could differ from each other by as much as several hundred kilograms.