Context : Double-lined , detached eclipsing binaries are our main source for accurate stellar masses and radii .
In this paper we focus on the 1.15–1.70 M _ { \sun } interval where convective core overshoot is gradually ramped up in theoretical evolutionary models .

Aims : We aim to determine absolute dimensions and abundances for the F-type detached eclipsing binary BK Peg , and to perform a detailed comparison with results from recent stellar evolutionary models , including a sample of previously studied systems with accurate parameters .

Methods : uvby light curves and uvby \beta standard photometry were obtained with the Strömgren Automatic Telescope , ESO , La Silla , and high-resolution spectra were acquired with the FIES spectrograph at the Nordic Optical Telescope , La Palma .

Results : The 5 \aas@@fstack { d } 49 period orbit of BK Peg is slightly eccentric ( e = 0.053 ) .
The two components are quite different with masses and radii of ( 1.414 \pm 0.007 M _ { \sun } , 1.988 \pm 0.008 R _ { \sun } ) and ( 1.257 \pm 0.005 M _ { \sun } , 1.474 \pm 0.017 R _ { \sun } ) , respectively .
The measured rotational velocities are 16.6 \pm 0.2 ( primary ) and 13.4 \pm 0.2 ( secondary ) km s ^ { -1 } .
For the secondary component this corresponds to ( pseudo ) synchronous rotation , whereas the primary component seems to rotate at a slightly lower rate .
We derive an iron abundance of [ \mathrm { Fe / H } ] = -0.12 \pm 0.07 and similar abundances for Si , Ca , Sc , Ti , Cr and Ni .
The stars have evolved to the upper half of the main-sequence band .
Yonsei-Yale and Victoria-Regina evolutionary models for the observed metal abundance reproduce BK Peg at ages of 2.75 and 2.50 Gyr , respectively , but tend to predict a lower age for the more massive primary component than for the secondary .
We find the same age trend for three other upper main-sequence systems in a sample of well studied eclipsing binaries with components in the 1.15–1.70 M _ { \sun } range .
We also find that the Yonsei-Yale models systematically predict higher ages than the Victoria-Regina models .
The sample includes BW Aqr , and as a supplement we have determined a [ \mathrm { Fe / H } ] abundance of -0.07 \pm 0.11 for this late F-type binary .

Conclusions : We propose to use BK Peg , BW Aqr , and other well-studied 1.15–1.70 M _ { \sun } eclipsing binaries to fine-tune convective core overshoot , diffusion , and possibly other ingredients of modern theoretical evolutionary models .