Thermal expansion of Ag-Bi1.6Pb0.4Sr2Ca2Cu3Ox structures was measured in the interval 20-830 degrees C using an inductive dilatometer. Two anomalies in the thermal-expansion curves of samples were discovered: a decrease in length Delta L/L on heating (740-810 degrees C) and an increase in Delta L/L on cooling (810-660 degrees C). Changes of composition, structure and electrical properties of Ag doped superconductor caused by heat treatments during thermal-expansion runs were examined using XRD, DTA, optical microscopy and resistivity measurements. A model explaining the observed results was discussed. Thermal-expansion coefficients of Ag doped and undoped BiPbSrCaCuO samples are 7.5 x 10(-6) K-1 (at 60-680 degrees C) and 6.4 x 10(-6)K(-1) (at 30-830 degrees C), respectively.