BMW 4 Series 420i Engine ReplacementCompare Prices & Get Quotes
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.
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12-Month Warranty
Nationwide Delivery
100+ Suppliers
From £1,800 to £3,200
Used from £1,500 · Reconditioned from £2,800 · Common codes: N20B20U0, B48B20A
From £1,500
Tested, bare/short engine
From £2,800
Rod bearings addressed, tested
From quote
Upgraded bearings, full teardown, revised valvetrain
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3 Simple Steps3 Simple Stepsto Finding the Best BMW 4 Series 420i Replacement Engineto Finding the Best BMW 4 Series 420i Replacement Engine
Most replacements completed within 3-5 days.
Variant HistoryBMW 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.
Variant HistoryBMW 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.
BMW 4 Series 420i
Fuel TypePetrol
Engine Size Range2.0L (1997-1998cc)
Power Output Range184hp consistently across all generationsEngine History Timeline
N20B20U0 2.0L turbocharged inline-four, 184hp, launch of F32 420i Coupe
F33 420i Convertible and F36 420i Gran Coupe join the range
B48B20A replaces N20B20U0 across all 420i body styles; LCI update brings improved timing chain design and Euro 6 compliance
G22 420i launched with B48B20B / B48B20M1 184hp, mild-hybrid technology on later models
present - G22 LCI 420i continues with refined B48 powertrain
Key Specs Snapshot
Fuel TypePetrolEngine Size Range2.0L (1997-1998cc)Power Output Range184hp consistently across all generationsYears Produced2013-presentEvery engine fitted to the BMW 4 Series 420i is covered below, with UK rebuilt pricing and known failure points.
BMW 4 Series 420i Engine Codes - Specifications & Replacement CostBMW 4 Series 420i Engine Codes - Specifications & Replacement Cost
2.0L Petrol Turbo (2013-2016)
Power Output184hp (135kW)Years Fitted2013-2016 (F32/F33/F36)
Compatible Trim Levels
- 420i SE
- 420i Sport
- 420i M Sport
- 420i Luxury
- 420i xDrive
Find your exact engine code, specs and UK replacement cost guide.
Used
Tested, ready-to-fit engine
£1,200-£2,200
Reconditioned
Addressed known issues, tested
£2,200-£3,800
Rebuilt
Full teardown, upgraded internals
£3,200-£5,000
Common Failure
Timing chain guide failure - the plastic guides can become brittle and break, leading to chain stretch and catastrophic engine damage if not addressed. Pre-2015 models are most vulnerable. Typical failure mileage: 60,000-90,000 miles.
The BMW 420i's engine reliability varies significantly by generation. Early N20-powered cars (2013-2016) are known for timing chain issues, while the B48 engine (2016 onwards) is considerably more robust. For 420i owners facing major engine failure, rebuilt engines through EnginesMarket include upgraded components addressing the original failure point, plus a minimum 12-month unlimited-mileage warranty.
Why the BMW 4 Series 420i N20 Engine Wears Prematurely
Affected Vehicles
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.
Why It Happens
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.
Dealer (parts + labour)
£1,800-£2,800
Specialist (parts + labour)
£1,200-£1,800
What it involves
Replace chain, guides, tensioner and oil pump drive module
Suitability
Best value if caught early - prevents engine destruction
1 - 2 daysDealer (parts + labour)
£7,000-£10,000
Specialist (parts + labour)
£3,200-£5,000
What it involves
Supply & fit, upgraded components addressing the original failure point, 12-month warranty
Suitability
If chain has already snapped or engine is damaged
1 - 2 daysAll prices are indicative UK market ranges based on current UK specialist supplier data.| Repair Tier | Dealer (Parts + Labour) | Specialist (Parts + Labour) | What It Involves | Suitability | Estimated Time |
|---|---|---|---|---|---|
 Preventative timing chain replacement Minor | £1,800-£2,800 | £1,200-£1,800 | Replace chain, guides, tensioner and oil pump drive module | Best value if caught early - prevents engine destruction | 1 - 2 days |
 Full Replacement - rebuilt/reconditioned engine Best Value | £7,000-£10,000 | £3,200-£5,000 | Supply & fit, upgraded components addressing the original failure point, 12-month warranty | If chain has already snapped or engine is damaged | 1 - 2 days |
Vehicle Value Check
Vehicle Value Check
Apply this UK-wide decision framework to your BMW 4 Series 420i: - Vehicle worth under ~£5,000: a used engine or preventative chain replacement typically makes more sense than a full rebuilt unit. - Vehicle worth ~£5,000-£8,000: evaluate both; reconditioned is viable if keeping the car 2+ years. - Vehicle worth ~£8,000-£15,000: reconditioned/rebuilt usually justifies the premium via warranty and reliability. - Vehicle worth £15,000+: replacement cost is typically small relative to vehicle value.
Our Recommendation
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.
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 rebuilt N20B20U0 BMW 4 Series 420i engine prices
12-Month Minimum
UK Specialists Vetted
Best Price GuidanceImportant Information
Important Information
"All prices are indicative UK market ranges based on historical quote data and repair requests from our network of engine specialists. Dealer pricing is estimated based on published main dealer labour rates and genuine OEM parts pricing. Specialist pricing reflects actual quote data from EnginesMarket's UK network. Actual costs vary depending on damage severity, vehicle condition, variant, and workshop location within the UK. Use our free comparison tool to get tailored quotes for your specific BMW 4 Series 420i. Every engine supplied through EnginesMarket carries a minimum 12-month unlimited mileage warranty - always confirm exact terms with your chosen supplier."
BMW 4 Series 420i Engine ReplacementFrequently Asked Questions
Question 1How 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
Question 2Does the BMW 4 Series 420i have timing chain problems-
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+
Question 3Is it worth replacing the engine in a BMW 4 Series 420i-
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
Question 4How do I know if my BMW 420i has the N20 or B48 engine-
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
Question 5How 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
Question 6What's the difference between the BMW 420i and 430i engines-
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)
Why Choose UsCompare BMW 4 Series 420iEngine PricesToday
1,000+ 420i engines supplied through our network
12-Month Warranty on every rebuilt 420i engine
Nationwide UK delivery
supply & fit available
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.
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