The paper reports the results of investigations on technological support of reliability indices for as-sembly units taking into account changes of contacting functional dimensions of single machine parts at the operation stage. At the heart of the work there is an analysis of dimension ties of an assembly unit ensuring a correlation between some basic stages of a product life cycle at which product quality is formed: designing with the quality parameter standardization of a surface and functional dimension accuracy, manufacturing with the definition of technological parameters and confirmation of accuracy achieved at separated operations and an operation at which changes of quality and accuracy parameters takes place.