BMW 324d / 324td Engine Replacement —Compare Prices &
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A reconditioned M21 engine typically costs £800–£2,500 supply only depending on which variant (naturally aspirated or turbocharged), with used units available from £500–£1,200. Fitting adds £700–£1,500. Use our calculator for a figure specific to your car. These engines are increasingly rare.

The naturally aspirated M21 in the 324d has a reputation for sturdiness and reliability. The turbocharged M21 in the 324td is less reliable — it suffers from cylinder head cracking and early electronic injection pump issues. Both engines require regular timing belt changes at 40,000-mile intervals — a snapped belt is catastrophic.

324d: timing belt failure (requires regular replacement). 324td: cylinder head cracking (the defining issue), timing belt failure, and early electronic injection pump failure (DDE system). The 324td's cylinder head is the single biggest concern.

These cars are rare and increasingly valuable — the 324td had the lowest production figures of any factory E30, with only around 27,000 units made. A well-kept example is worth £5,000–£15,000+ depending on condition. A £1,500–£2,500 recon is only 15–30% of the car's value — well within the 70% BMW threshold. Replacement is almost always worthwhile on a cherished example.

The engine code is M21D24 — both variants share the same core engine. The naturally aspirated version is fitted to the 324d (1985–1990); the turbocharged version is fitted to the 324td (1987–1993). The 324td was never officially sold in the UK, so most UK cars are private imports.

The timing belt must be replaced — it's a wear item. Replacement interval is 40,000 miles or 6 years. If the belt snaps, the engine is typically destroyed. A preventative belt replacement (£300–£600) is far cheaper than a full engine replacement (£800–£2,500+). At the first sign of ticking from the front of the engine, book an inspection immediately.