BMW N47 (1.6 and 2.0)

The four-cylinder common-rail diesel that carried BMW's volume diesel range for seven years, replacing the M47 and replaced in turn by the B47. Its defining characteristic is the timing chain at the rear of the engine, against the bulkhead — a layout that makes a stretched or failed chain a gearbox-out job rather than a front-cover job, and turns a cheap part into one of the most expensive repairs on the car.

That matters diagnostically because the warning is auditory rather than electronic: a rattle on cold start from the back of the engine precedes any stored code, and by the time timing correlation faults appear the damage is usually done. Treat a rear-of-engine cold rattle on an N47 as urgent even with nothing logged.

Swirl-flap and inlet-manifold carbon are the other recurring theme, and the intake tract is worth inspecting whenever a running complaint arrives without a clean electrical explanation.

It is sold at two sizes — the N47D16 at 1.6, which is the Mini diesel, and the N47D20 at 2.0 everywhere else. The rear timing chain above is common to both, so the cold-start rattle and the gearbox-out cost apply to a Mini exactly as they do to a 3 Series.