  We present new V and R-passband CCD photometry of UU Sge and V477 Lyr, the
eclipsing binary nuclei of the planetary nebulae Abell 63 and Abell 46,
respectively. We have performed a simultaneous analysis of VR light-curves and
estimated the effective temperatures for the primary and secondary stars to be
78 000 $\pm$ 3000 and 6136 $\pm$ 240 K for UU Sge, 49 500 $\pm$ 4500 and 3874
$\pm$ 350 K for V477 Lyr. We have also reanalysed the previously measured
radial velocities and combined the results with those obtained from the
analysis of the light curves to derive absolute parameters of the components.
The secondary stars have larger radii than expected from their main--sequence
counterparts at the same masses. We have determined the post--common envelope
ages and the thermal time scales of the systems and examined the possible
reasons of expanded radius of the secondary components, together with some
selected post-common envelope binaries. We conclude that the secondary
components of the nuclei of the planetary nebulae are still out of thermal
equilibrium along with two post-common envelope systems: HS 1136+6646 and RE
1016-053. For other systems, magnetic activity has been suggested as the more
plausible reason for their expanded radii. We have also estimated the
common--envelope efficiency parameters of UU Sge and V477 Lyr.
