BMW Z1 25i Engine Replacement Compare Prices & Get Quotes

A full BMW Z1 25i engine replacement typically costs £2,500-£6,000 supply-only for a rebuilt M20B25 unit, or £4,000-£6,500 fitted by a specialist.

• Used M20B25 engines: £1,200-£2,500 depending on mileage and condition
• Reconditioned units: £2,200-£4,000
• Professional fitting adds £1,000-£2,000 to the engine cost

The M20B25 is one of BMW's most robust and characterful straight-six engines, shared with the E30 325i. However, Z1-specific issues exist: the unique cylinder-head oil-feed restriction starves the valvetrain on 1989-1991 models, and the under-body exhaust heat-shield failure cooks starter motors. The Z1 sits 40mm lower than the E30, flattening the sump angle and causing oil starvation at low RPM - a fault never seen in the E30. Regular maintenance, particularly timing belt replacement every 60,000 miles, is essential.

The M20B25 uses a rubber timing belt that must be replaced every 60,000 miles or 5 years. Warning signs include:

• No warning - the belt typically snaps without prior symptoms
• Rattling or squealing noise from the front of the engine
• Engine misfire or loss of power if belt has jumped a tooth
• Complete engine seizure - if the belt snaps, pistons strike valves

For a Z1 25i worth £20,000-£50,000, a £2,500-£5,000 rebuilt engine is typically good value - replacement cost is small relative to vehicle value.

• Compare replacement cost against vehicle value - replacement is viable up to approximately 70% of the car's value
• Given the vehicle's collector-car status, specialist rebuild with warranty is the safest option
• Always factor the 12-month warranty into your replacement decision

The Z1 sits 40mm lower than the E30 325i, which flattens the sump angle and alters oil pickup geometry. This causes oil starvation at low RPM, leading to camshaft lobe pitting and wear - a fault never seen in the E30.

• Symptoms include ticking or tapping from the top end
• Camshaft pitting is visible on inspection
• The fix is an up-rated oil pump (OEM 11 41 1 730 302) and hardened 731 camshaft

Engine swaps to a different size or type are technically complex and rarely cost-effective for the Z1 25i:

• The M20B25 is the only engine fitted to the Z1 from the factory - stick to like-for-like replacement
• Swapping to an M50 or S50 requires different ECU, wiring, engine mounts, and transmission
• The Z1's unique chassis and low ride height make non-standard swaps extremely difficult
• Insurance must be notified of any non-standard engine swap
• Our marketplace only recommends like-for-like code-matching for warranty coverage