How much does a BMW 4 Series 420i engine replacement cost in the UK-

A full BMW 420i engine replacement typically costs between £1,800 and £5,800 for the engine itself, depending on whether you choose used, reconditioned or rebuilt. Specialist fitting adds £650-£910 in labour. Used N20B20U0: £1,200-£2,200. Reconditioned B48B20A: £2,800-£4,500. Rebuilt B48B20A: £3,800-£5,800.

How long does a BMW 4 Series 420i engine replacement take-

A typical BMW 420i engine replacement takes 10-14 hours of workshop labour. With parts sourcing and scheduling, allow 2-5 working days from order to completion. Supply-only: 1-3 working days for delivery. Supply & fit: 3-5 working days total.

BMW 420i SPECIALISTS

BMW 4 Series 420i Engine Replacement Compare Prices & Get Quotes

Q: How do I know if my BMW 420i has the N20 or B48 engine-

The engine change happened during 2016, with LCI models featuring the B48. The easiest way to check is by decoding your VIN - the last seven digits will reveal the engine code. Alternatively, the B48 has a noticeably different engine cover design. Pre-2016 models typically have the N20B20U0. 2016-onwards LCI models have the B48B20A.

Get instant quotes today from trusted UK BMW 4 Series 420i engine specialists. Compare prices on reconditioned, rebuilt and used engines for your 420i - whether you drive a Coupe, Convertible or Gran Coupe.

Supply & Fit Available

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BMW 4 Series 420i Engine

from£1,800 to £3,200

Usedfrom £1,500
Reconditionedfrom £2,800
Common codesN20B20U0, B48B20A

BMW 4-series 420i Used Engine — N20B20U0

BMW 4-seriesUsed Engine — N20B20U0

BMW 4-series 420i Reconditioned Engine — N20B20U0

BMW 4-seriesReconditioned Engine — N20B20U0

BMW 4-series 420i Rebuilt Engine — N20B20U0

BMW 4-seriesRebuilt Engine — N20B20U0

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How it works

3 Simple Steps to Finding the Right Replacement Engine

Clear information first, then the right engine and specialist for your exact vehicle.

Variant History

BMW 4 Series 420i Engine History & Specs at a Glance

The BMW 420i launched as the entry-level petrol variant of the first-generation 4 Series (F32/F33/F36) in November 2013, powered initially by the N20 four-cylinder turbo. In 2016, BMW replaced the N20 with the more robust B48 engine as part of the Life Cycle Impulse (LCI) update, bringing improved reliability and emissions compliance. The second-generation G22 420i (2020-present) continues with an updated B48 variant.

2013
N20B20U0, 2.0L turbocharged inline-four, 184hp, launch of F32 420i Coupe
2014
F33 420i Convertible and F36 420i Gran Coupe join the range
2016
B48B20A replaces N20B20U0 across all 420i body styles; LCI update brings improved timing chain design and Euro 6 compliance
2020
G22 420i launched with B48B20B / B48B20M1, 184hp, mild-hybrid technology on later models
2024
present - G22 LCI 420i continues with refined B48 powertrain

Every engine fitted to the BMW 4 Series 420i is covered below, with UK rebuilt pricing and known failure points.

Compatible Engines

BMW 4 Series 420i Engine Codes Specifications & Replacement Cost

Find your exact engine code, specs and UK replacement cost guide.

N20B20U0 — 2.0L Petrol Turbo (2013-2016)

Power Output: 184hp (135kW)
Years Fitted: 2013-2016 (F32/F33/F36)

Can’t find your exact engine code?-> Get quotes for N20B20U0 BMW 4 Series 420i engine replacement

-> Get quotes for N20B20U0 BMW 4 Series 420i engine replacement

Common failure points and repair options

Timing Chain Failure

Affected: BMW 4 Series 420i (N20B20U0, 2013-2016)
Typical failure mileage: 60,000-90,000 miles

Root cause

Plastic timing chain guides become brittle with heat cycling and oil degradation, causing them to break. The chain then stretches or snaps, leading to valve/piston interference and catastrophic engine damage.

Repair options

Repair tier	Dealer price	Specialist price
Preventative timing chain replacement	£1,800-£2,800	£1,200-£1,800
Full Replacement - rebuilt/reconditioned engine	£7,000-£10,000	£3,200-£5,000

Our recommendation

If you hear a rattling noise on cold start from your N20-powered 420i, act immediately - a £1,200-£1,800 preventative chain replacement is far cheaper than a £3,200+ engine replacement. For B48-powered cars (2016 onwards), the risk is significantly lower, but regular oil changes using the correct BMW Longlife spec are essential.

-> Compare rebuilt N20B20U0 BMW 4 Series 420i engine prices

Oil Consumption & Valve Stem Seal Wear

Affected: BMW 4 Series 420i (N20B20U0 2013-2016, B48B20A 2016-2020)
Typical failure mileage: 60,000-120,000 miles

Root cause

On N20 engines, valve stem seals can harden and allow oil past the valves. On B48 engines, excessive consumption may indicate worn piston rings or PCV system issues.

Repair options

Repair tier	Dealer price	Specialist price
PCV system inspection/replacement	£400-£800	£200-£400
Valve stem seal replacement	£2,000-£3,500	£1,200-£2,000
Full engine rebuild/replacement	£7,000-£10,000	£3,200-£5,800

Our recommendation

Monitor oil levels regularly - the B48 typically consumes 0.5-1 litre per 10,000 miles, which is within normal parameters. If consumption exceeds this, start with a PCV system inspection (£200-£400) before committing to more expensive work.

-> Compare rebuilt B48B20A BMW 4 Series 420i engine prices

Don't Let Engine Failure Write Off Your BMW 4 Series 420i

Every BMW 420i engine supplied through EnginesMarket carries a minimum 12-month unlimited-mileage warranty - whether you choose a used, reconditioned or rebuilt unit. Our network of vetted UK specialists offers nationwide delivery and supply & fit options, often at 40-60% below main dealer pricing. Don't scrap your 420i over a failed engine - compare specialist quotes today.

Compare BMW 4 Series 420i Engine Replacement Prices Now ->

FAQ

BMW 4 Series 420i Engine ReplacementFrequently Asked Questions

Everything BMW 4 Series 420i owners usually ask before choosing a rebuilt, reconditioned or used replacement engine.

Early N20-powered 420i models (2013-2016) are known for timing chain guide failure, typically between 60,000-90,000 miles. The B48 engine introduced in 2016 addressed this design flaw and is significantly more reliable.

Rattling noise on cold start is the primary warning sign
Preventative chain replacement costs £1,200-£1,800 at a specialist
Ignoring the issue can lead to catastrophic engine failure costing £3,200+

-> Check your BMW 420i engine code now

For a 420i worth over £8,000, a reconditioned or rebuilt engine (£2,800-£5,800) is a sound investment that can extend the car's life by 100,000+ miles. For cars under £5,000, a used engine (£1,200-£2,200) with a preventative timing chain replacement before fitting is often the most cost-effective route.

Always factor in fitting costs (£650-£910)
Every engine through EnginesMarket comes with a 12-month warranty

-> Compare BMW 420i engine options

The engine change happened during 2016, with LCI (Life Cycle Impulse) models featuring the B48. The easiest way to check is by decoding your VIN - the last seven digits will reveal the engine code. Alternatively, the B48 has a noticeably different engine cover design.

Pre-2016 models typically have the N20B20U0
2016-onwards LCI models have the B48B20A

-> Enter your registration above to check your engine code

The 420i uses a 2.0-litre four-cylinder turbo producing 184hp, while the 430i uses a higher-output version of the same B48 engine producing 258hp. Both are from the same engine family, but the 430i has different turbocharger calibration and internals.

420i: more fuel-efficient, lower purchase cost
430i: significantly faster (0-62mph in 5.6s vs 7.3s)
Engine codes differ: B48B20A (420i) vs B48B20B (430i)

-> Compare BMW 4 Series engine options

Why Choose Us

Compare BMW 4 Series 420i Engine Prices Today

Comparing quotes for your BMW 4 Series 420i engine replacement is free, no-obligation, and specific to your exact engine code - whether you need a used N20, a reconditioned B48, or a fully rebuilt unit with warranty. Our network of vetted UK specialists offers transparent pricing, nationwide delivery, and supply & fit options to get your 420i back on the road with minimum hassle.

1,000+1,000+ 420i engines supplied through our network

12-Month12-Month Warranty on every rebuilt 420i engine

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