Bapcor, the owner of some of the country’s best known car parts retailers, has warned of weaker than expected earnings in a pessimistic update to investors that included big write-offs and the exit of three directors.

Angus McKay, Bapcor’s chief executive, took the helm in August soon after the board rejected a $1.83 billion buyout proposal from Bain Capital, and said that turning the struggling company around had been harder than expected. Investors wiped almost $500 million from its sharemarket value.