BMW 1 Series F21Hatchback2011–2019
Every engine fitted to the 1 Series F21 three‑door — from the entry‑level 114i to the fire‑breathing M135i and M140i six‑cylinders, and the full range of N47 and B47 diesel fours that define UK ownership.
Real UK costs, honest failure data, and the 2015 facelift engine refresh that brought BMW’s modular B‑series engines to the range.
Backed by 344+ real UK F20/F21 enquiries in 2025 [BMW‑VERIFIED].
Engine Database
Every engine fitted to the F21 three‑door — from the pre‑LCI N‑series engines to the post‑2015 B‑series modular family that brought three‑cylinder power to the range.
Overview
The BMW 1 Series F21 is the three‑door hatchback variant of the second‑generation 1 Series, produced from September 2011 to May 2019. Built on BMW’s L7 platform and featuring rear‑wheel drive for most models (with xDrive all‑wheel drive available as an option), the F21 offered a wide range of turbocharged petrol and diesel engines.
A significant 2015 facelift (LCI) brought BMW’s modular B‑series engine family to the range, replacing the N‑series engines with more efficient three‑ and four‑cylinder units. The range was topped by the M135i and later M140i, featuring 3.0‑litre six‑cylinder turbocharged engines that made the F21 one of the most engaging hot hatchbacks of its era.
Key Facts
Market Intelligence
The BMW 1 Series F20/F21 generated 344 real UK engine enquiries in 2025 [EM‑VERIFIED], concentrated on the N47 diesel fours as the parc exits affordable‑warranty age and timing‑chain concerns come to the fore.
04Best & Worst Engines
Best Diesel Overall
B47D20A (post‑2015, 118d/120d)
““The B47 is BMW’s modular diesel four — front‑mounted timing chain, far more accessible than the N47’s rear‑mounted design, and generally regarded as a strong and dependable engine capable of high mileage if properly maintained.” Who it’s for: buyers who want diesel economy without the N47’s timing‑chain anxiety.”
Best Petrol Overall
B58B30A (M140i, 2016–2019)
““The B58 is BMW’s modular straight‑six masterpiece — 340 bhp, silky smooth, and chain‑driven with a robust bottom end. It’s the engine that made the M140i the hot hatch benchmark. The most reliable engine in the F21 range.” Who it’s for: buyers who want six‑cylinder performance without the N55’s fuel‑pump anxieties.”
Highest Risk
N47D20C (pre‑2015, 116d/118d/120d)
““The rear‑mounted timing chain is the defining risk of the pre‑LCI diesel four — cold‑start rattle is the warning, and a snapped chain means full replacement. The N47 is the single biggest ownership risk on the F21.” Who it’s for: only buyers with documented chain‑replacement history.”
Most Expensive Failure
N47D20D / N47S1 (125d, pre‑2015)
““The high‑output N47 in the 125d carries the same rear‑chain risk as the lower‑output variants, but with more power and higher stresses. A snapped chain in a 125d means the same £3,500–£6,000 replacement.” Who it’s for: 125d buyers with deep pockets and full service history.”
Best Value
B47D20A (post‑2015, 118d/120d)
““The B47 is the N47’s successor — front‑mounted chain, better oil supply, and significantly lower risk of catastrophic failure. It’s the diesel four you can buy without anxiety.” Who it’s for: buyers who want modern diesel efficiency without the N47’s caveats.”
Most Overlooked
B48B20A (120i, 2016–2019)
““The B48 is the four‑cylinder petrol that replaced the N13 — 184 bhp, chain‑driven, and significantly more reliable than the N13 it replaced. It’s the sweet spot of the petrol range.” Who it’s for: buyers who want petrol refinement without the M140i’s running costs.”
Best Diesel Overall
B47D20A
(post‑2015, 118d/120d)
““The B47 is BMW’s modular diesel four — front‑mounted timing chain, far more accessible than the N47’s rear‑mounted design, and generally regarded as a strong and dependable engine capable of high mileage if properly maintained.” Who it’s for: buyers who want diesel economy without the N47’s timing‑chain anxiety.”
Best Petrol Overall
B58B30A
(M140i, 2016–2019)
““The B58 is BMW’s modular straight‑six masterpiece — 340 bhp, silky smooth, and chain‑driven with a robust bottom end. It’s the engine that made the M140i the hot hatch benchmark. The most reliable engine in the F21 range.” Who it’s for: buyers who want six‑cylinder performance without the N55’s fuel‑pump anxieties.”
Highest Risk
N47D20C
(pre‑2015, 116d/118d/120d)
““The rear‑mounted timing chain is the defining risk of the pre‑LCI diesel four — cold‑start rattle is the warning, and a snapped chain means full replacement. The N47 is the single biggest ownership risk on the F21.” Who it’s for: only buyers with documented chain‑replacement history.”
Most Expensive Failure
N47D20D
/ N47S1 (125d, pre‑2015)
““The high‑output N47 in the 125d carries the same rear‑chain risk as the lower‑output variants, but with more power and higher stresses. A snapped chain in a 125d means the same £3,500–£6,000 replacement.” Who it’s for: 125d buyers with deep pockets and full service history.”
Best Value
B47D20A
(post‑2015, 118d/120d)
““The B47 is the N47’s successor — front‑mounted chain, better oil supply, and significantly lower risk of catastrophic failure. It’s the diesel four you can buy without anxiety.” Who it’s for: buyers who want modern diesel efficiency without the N47’s caveats.”
Most Overlooked
B48B20A (120i, 2016–2019)
““The B48 is the four‑cylinder petrol that replaced the N13 — 184 bhp, chain‑driven, and significantly more reliable than the N13 it replaced. It’s the sweet spot of the petrol range.” Who it’s for: buyers who want petrol refinement without the M140i’s running costs.”
Engine
Typical Mileage
Common Major Failure
Repair Cost (Specialist)
Replacement Cost (Recon)
Ownership Verdict
Risk vs Reward -budget for chain history
Solid Choice -reliable when maintained
Performance Choice -fast, costlier to maintainBest Petrol Value -modern, reliableSolid Petrol -reliable, efficientBest Petrol -the M140i’s defining assetHighest Risk -chain is the limiting factorHighest Risk -cold‑start rattle is the warning
Most Expensive -more power, same riskSolid Choice -modern three‑cylinder dieselBest Diesel -chain accessible, robustSolid Choice -224 bhp, chain accessibleEngineTypical MileageCommon Major FailureRepair Cost (Specialist)Replacement Cost (Recon)Ownership VerdictRisk vs Reward -budget for chain historySolid Choice -reliable when maintainedPerformance Choice -fast, costlier to maintainBest Petrol Value -modern, reliableSolid Petrol -reliable, efficientBest Petrol -the M140i’s defining assetHighest Risk -chain is the limiting factorHighest Risk -cold‑start rattle is the warningMost Expensive -more power, same riskSolid Choice -modern three‑cylinder dieselBest Diesel -chain accessible, robustSolid Choice -224 bhp, chain accessible
The F21 rule
A £3,200–£5,500 N47 recon against a £4,000–£12,000 F21 sits at 27–137% of the car’s value. On a sub‑£5,000 F21, that brushes our 70% BMW threshold -we’ll honestly tell you to walk away. Against a well‑kept £10,000+ example, the same recon drops to a routine 32–55% -a repair decision, not a financial one. Value the car first.
N47
Timing Chain Stretch (pre‑2015 diesel fours)
Affected models:
F21 114d, 116d, 118d, 120d, 125d (2011–2015).
Typical failure mileage:
60,000–100,000 miles.
Root cause:
The rear‑mounted timing chain receives the last oil feed and is tensioned by a plastic guide that degrades over time -cold‑start rattle for 1–2 seconds is the classic early warning. This affects the entire N47 family, including the high‑output N47D20D in the 125d.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£1,800–£2,500
£650–£1,800
Catastrophic (Replacement)
Dealer
Specialist
£6,000–£8,000
£3,200–£5,500
Our Recommendation
At the first sign of cold‑start rattle on any N47‑powered F21, get the chain inspected immediately -a £650–£1,800 preventative repair is dramatically cheaper than the £3,200–£5,500 replacement that follows if ignored. On an F21 worth under £5,000, this decision alone determines whether the car stays economically viable.
N13
Timing Chain Tensioner Wear (pre‑2015 petrol fours)
Affected models:
F21 114i, 116i, 118i (2011–2015).
Typical failure mileage:
60,000–100,000 miles.
Root cause:
The N13 (BMW’s version of the Prince engine) can suffer from timing chain tensioner wear, leading to chain slack and rattle on start‑up. If ignored, the chain can jump or snap, causing catastrophic engine damage.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£1,500–£2,200
£650–£1,800
Catastrophic (Replacement)
Dealer
Specialist
£5,000–£7,000
£1,500–£3,500
Our Recommendation
On any pre‑2015 petrol F21, have the timing chain tensioner inspected at 60,000 miles -a £650–£1,800 preventative repair is far cheaper than the £1,500–£3,500 replacement that follows a snapped chain. The N13 is otherwise a robust engine, but this single weak point defines its ownership experience.
N55
HPFP & Injector Failure (M135i)
Affected models:
F21 M135i (2012–2016).
Typical failure mileage:
30,000–80,000 miles.
Root cause:
The high‑pressure fuel pump’s internal wear leads to fuel pressure loss, hard starting, and eventual engine damage if ignored; injector issues frequently follow. This is the M135i’s defining ownership cost risk.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£1,200–£1,800
£800–£1,500
Catastrophic (Replacement)
Dealer
Specialist
£7,000–£9,000
£4,500–£7,500
Our Recommendation
If your M135i has no documented HPFP history, treat it as overdue preventative maintenance -£800–£1,500 now is far cheaper than the £4,500+ replacement that follows a lean‑running failure. This is the single most important maintenance item on the N55.
B38/B37
Engine Mount Wear (LCI three‑cylinders)
Affected models:
F21 116i, 118i, 114d, 116d (2015–2019).
Typical failure mileage:
50,000–80,000 miles.
Root cause:
The three‑cylinder engines (B38 petrol, B37 diesel) are inherently less balanced than four‑ or six‑cylinder units. This can lead to premature wear of the engine mounts, resulting in increased vibration and noise in the cabin.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£400–£700
£200–£400
Catastrophic (Replacement)
Dealer
Specialist
N/A
N/A
Our Recommendation
This is a minor but common issue on three‑cylinder F21s -a £200–£400 mount replacement restores the car’s refinement and is one of the cheapest fixes on the range. The B38 and B37 engines themselves are robust and chain‑driven; this is the only recurring issue.
VariantEngine Code
Used (Supply)
Reconditioned (Supply)
Rebuilt (Supply)
Labour HoursNo Generation variance from the Model Page’s baseline figures -F21 shares its engine‑bay layout with the F20 5‑door, so costs are inherited directly per the Authority Model, with no divergence note required. N47 and B47 costs are carried forward from the Model Page’s existing cost tables.
Scope note: All variants listed are F21 3‑door hatchback only. The 125i was offered with the N20B20 engine producing 218 bhp (pre‑LCI) and later 238 bhp. The M135i (pre‑LCI) used the N55B30A six‑cylinder producing 326 bhp. The M140i (LCI) used the B58B30A producing 340 bhp. The 120i was offered with the N13 (pre‑LCI, 177 bhp) and later the B48 (LCI, 184 bhp). The 125d was offered with the N47D20D (pre‑LCI, 218 bhp) and later the B47D20B (LCI, 224 bhp). The 114d and 116d were offered with the N47D16A/N47D20C (pre‑LCI) and later the B37D15A (LCI).
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£2,800–£5,500 supply only
[BMW‑QUOTE]
Most Common Failures
Live FeedBMW 120d F21
N47
ManchesterCold‑start rattle6
enquiries
Updated MonthlyBMW M135i F21
N55
BirminghamHPFP failure4
enquiries
Updated MonthlyBMW 118i F21
N13
LondonTiming chain rattle3
enquiries
Updated MonthlyMost Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£2,800–£5,500 supply only
[BMW‑QUOTE]
Most Common Failures
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£2,800–£5,500 supply only
[BMW‑QUOTE]
Most Common Failures
Scope note: All variants listed are F21 3‑door hatchback only. The 125i was offered with the N20B20 engine producing 218 bhp (pre‑LCI) and later 238 bhp. The M135i (pre‑LCI) used the N55B30A six‑cylinder producing 326 bhp. The M140i (LCI) used the B58B30A producing 340 bhp. The 120i was offered with the N13 (pre‑LCI, 177 bhp) and later the B48 (LCI, 184 bhp). The 125d was offered with the N47D20D (pre‑LCI, 218 bhp) and later the B47D20B (LCI, 224 bhp). The 114d and 116d were offered with the N47D16A/N47D20C (pre‑LCI) and later the B37D15A (LCI).
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£2,800–£5,500 supply only
[BMW‑QUOTE]
Most Common Failures
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£2,800–£5,500 supply only
[BMW‑QUOTE]
Most Common Failures
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£2,800–£5,500 supply only
[BMW‑QUOTE]
Most Common Failures
Live FeedBMW 120d F21
N47
ManchesterCold‑start rattle6
enquiries
BMW M135i F21
N55
BirminghamHPFP failure4
enquiries
BMW 118i F21
N13
LondonTiming chain rattle3
enquiries
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