Renault K4M / K7M

The petrol members of Renault's K-family — the 1.4 and 1.6 litre engines of the Clio, Mégane, Scénic, Logan, Duster and Sandero, and among the most numerous engines in Eastern Europe, North Africa and South America.

Simple, belt-driven and port-injected, with the 8-valve K7M being about as uncomplicated as a modern engine gets. The diagnostic profile is old-fashioned in a useful way: ignition coils, the crankshaft position sensor, the idle control and vacuum leaks account for most running complaints, and physical testing beats scan data because the codes are few and general.

The timing belt is the item that ends these engines, and on the interference designs a snapped belt is terminal. In the markets where these cars are most common the cars are old, records are thin, and an unknown belt history should be treated as a job due rather than an unknown — that single piece of advice prevents more destroyed K-family engines than any diagnostic technique.