A machine for the preparation of liquid products via capsules having a delivery assembly, which comprises a stationary structure and a passage for introduction of capsules, the assembly moreover comprising: - a preparation chamber, which includes a first part of chamber, having a housing configured for receiving at least partially a capsule and enabling delivery of the liquid product from the preparation chamber, and a second part of chamber configured for introduction of the fluid into the capsule; - an actuation system controllable for causing displacements of the second part of chamber with respect to the first part of chamber between a spaced apart position and a close position; - two first guide elements, secured at generally opposite side parts of the second part of chamber and fixed in motion with respect to the second part of chamber, the first guide elements being configured for co-operating with a flange of a capsule for guiding the latter towards a position that is substantially coaxial to the first part of chamber and to the second part of chamber, the first guide elements being designed to keep the capsule in a position centred with respect to the first part of chamber in the course of displacement of the second part of chamber towards the close position, at least as far as entry of the capsule into the housing of the first part of chamber, wherein each first guide element has at least one first portion that generally faces a front of the second part of chamber at a distance therefrom, such that said first portion and said front define therebetween a space for receiving the flange of the capsule, to guide the capsule towards said position that is substantially coaxial to the first part of chamber and to the second part of chamber and to keep the capsule in said centred position, at least as far as entry of the capsule into the housing of the first part of chamber, the machine being characterized in that it further comprises means (17, 8g, 8h) for bringing about a momentary increase in the distance between the aforesaid first portion of each first guide element and the front of the second part of chamber, in the course of displacement of the second part of chamber from the close position to the spaced apart position. - a preparation chamber, which includes a first part of chamber, having a housing configured for receiving at least partially a capsule and enabling delivery of the liquid product from the preparation chamber, and a second part of chamber configured for introduction of the fluid into the capsule; - an actuation system controllable for causing displacements of the second part of chamber with respect to the first part of chamber between a spaced apart position and a close position; - two first guide elements, secured at generally opposite side parts of the second part of chamber and fixed in motion with respect to the second part of chamber, the first guide elements being configured for co-operating with a flange of a capsule for guiding the latter towards a position that is substantially coaxial to the first part of chamber and to the second part of chamber, the first guide elements being designed to keep the capsule in a position centred with respect to the first part of chamber in the course of displacement of the second part of chamber towards the close position, at least as far as entry of the capsule into the housing of the first part of chamber,