In this weekly diary study, we integrated research on job crafting to explore the associations between expansion and contraction oriented relational job crafting, work engagement and manager-rated employee behaviours (work performance and voice). Furthermore, we investigated cross-level moderations of prosocial and impression management motives on our proposed associations. We tested our hypotheses with matched data collected over seven weeks in Istanbul, Turkey. The results from multilevel analyses revealed that (a) expansion oriented relational job crafting is positively related with work performance and voice via work engagement, while (b) contraction oriented relational job crafting is negatively related with work performance and voice via work engagement, all measured at the week level. Furthermore, impression management motives of employees moderated the association between expansion oriented relational job crafting and work engagement in that this positive association is stronger for employees low on impression management motives. Our results contribute to job crafting research in two ways. First, it focuses on relational job crafting and discusses how and why the two opposite types of relational job crafting (expansion versus contraction oriented) impact on work engagement and employees' key outcomes in the way they do. This addresses the question 'is there a dark side to job crafting?' Second, it focuses on the importance of context and integrates two motives relevant to understand how relational job crafting unfolds, thereby taking a step to address questions for whom (i.e. what kinds of employees), relational job crafting is more effective and translates into enhanced (vs deteriorated) work outcomes. Moreover, our use of a weekly within-person design adds to a recently growing research stream emphasizing the dynamic nature of job crafting.