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BMW N46B20 Engine - Replacement Cost, Problems & CompatibilityProblems & Compatibility
BMW's 2.0-litre naturally aspirated four-cylinder that powered the 1 Series, 3 Series, 5 Series, X1 and X3 from 2004 to 2015 - the valvetronic successor to the N42. A smooth, high-revving engine with a well-documented appetite for oil and timing chain wear. Reconditioned N46B20 units from £1,500 , with consistent UK demand across the N46 family.
Supply & Fit Available
12-Month Warranty
Nationwide Delivery
100+ Suppliers
Used from
£800
Reconditioned from
£1,500
Rebuilt from
£2,500
GB
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Key Specs
BMW N46B20 - Specifications at a Glance
Engine Code
N46B20 (covers N46B20, N46B20B, N46B20U1, N46B20U2, N46N)
Fuel
Petrol
Configuration
2.0L inline-4, DOHC, 16 valves, Valvetronic, Double VANOS
Power Output(s)
129-150 hp (95-110 kW); 180-200 Nm torque
Years Produced
2004-2015
UK Models Fitted
7+ BMW models - full list in Compatibility below
2025 UK Replacement Requests
Replaced
BMW N42 (2001-2004)
Replaced By
BMW N43 (direct-injected) / N13 (turbocharged)
Most Common Failure
Valve stem seal wear (oil consumption); timing chain tensioner failure
Reconditioned Price Range
£1,500-£2,500 supply-only
Vetted UK specialists for N46B20 replacements
Minimum 12-month warranty on reconditioned and rebuilt options
Fitted To
Which BMW Models Use the N46B20-
The N46B20 was BMW's core 2.0-litre four-cylinder from 2004 to 2015, fitted across the 1 Series, 3 Series, 5 Series, X1 and X3 generations. It replaced the N42 and was itself replaced by the direct-injected N43 (in markets with low-sulphur fuel) and the turbocharged N13. The engine appeared in multiple states of tune from 129 hp to 150 hp depending on the model and market.
| Model | Generation/Chassis | Badge(s) | Years | Link |
|---|---|---|---|---|
 BMW 1 Series | E81 / E87 | 118i, 120i | 2004-2011 | |
 BMW 3 Series | E46 | 318i, 318Ci, 318ti | 2004-2005 | |
| BMW 3 Series | E90 / E91 | 318i, 320i | 2004-2011 | |
 BMW 5 Series | E60 / E61 | 520i | 2004-2010 | |
 BMW X1 | E84 | sDrive18i, sDrive20i, xDrive20i | 2009-2015 | |
 BMW X3 | E83 | xDrive20i | 2004-2010 | |
| BMW Z4 | E85 / E86 | Z4 2.0i | 2004-2008 |
02
BMW 3 Series
03
BMW 3 Series
04
BMW 5 Series
05
BMW X1
06
BMW X3
07
BMW Z4
CROSS-BRAND
N46B20 is documented across 7 BMW applications spanning BMW 1 Series, BMW 3 Series, BMW 5 Series, BMW X1, BMW X3, BMW Z4. Registration lookup confirms the exact suffix before quotes are sent.
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Not sure which engine your car has- Enter your registration above - we'll confirm your exact N46 variant before any quotes are sent.
Prices
BMW N46B20 Engine Replacement Cost (UK)
Condition | Supply Only | Fitted (Independent Specialist) | Typical Warranty |
|---|---|---|---|
Used | £800-£1,200 | £1,200-£1,700 | 3-6 months |
Reconditioned | £1,500-£2,500 | £1,900-£3,000 | 12-24 months |
Rebuilt | £2,500-£4,000 | £2,900-£4,500 | 12-24 months |
The biggest price movers for an N46B20 replacement are whether the valve stem seals have been replaced (the engine's most common failure), the condition of the timing chain and tensioner, and whether the VANOS and Valvetronic systems are functioning correctly. Engines with documented oil consumption history and timing chain work command a premium. See our full /prices/reconditioned-engine-cost guide for more detail.
Labour Guide
Fitting an N46B20 typically takes 8-12 hours at £65-£91/hr (independent BMW specialist) - the Valvetronic system and tight engine bay add complexity over simpler four-cylinder engines.
Price Factors
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Common Problems
BMW N46B20 Engine Problems - What Actually Fails
Every engine has its weak points. Here are the known issues with the N46B20, based on real-world data and verified failure patterns.
Verified issue focus: Valve stem seal wear (oil consumption); timing chain tensioner failure.
1. Valve Stem Seal Wear - the signature N46 oil consumption issue
1. Valve Stem Seal Wear - the signature N46 oil consumption issue
Typical onset:
60,000-120,000 miles
What happens:
Worn valve stem seals are a very common cause of excessive oil consumption on the N46 engine. As the seals deteriorate and become rigid, they allow oil to pass into the combustion chamber. Symptoms include blue smoke from the exhaust after idling (particularly following a 10-minute idle then revving to 4,000 rpm), oil consumption of up to 1 litre per 300 miles, and occasional misfires.
Repair vs replace:
Valve stem seal replacement can be performed with the engine in situ using specialist tools, typically costing £1,000-£1,700 at a specialist. If oil consumption is severe (1 litre per 200-300 km), piston rings may also be compromised, in which case a full rebuild or replacement is justified. Read our full /failures/valve-stem-seal-failure guide
Read more about this issue
2. Timing Chain Tensioner and Guide Failure
2. Timing Chain Tensioner and Guide Failure
Typical onset:
80,000-150,000 miles
What happens:
The N46, along with the N42, N43 and N45 engines, is particularly known for timing chain problems. The original tensioner was too short, allowing the chain to become slack and rub against the guides. A broken tensioner can cause the timing chain to slip, leading to incorrect timing and drivability issues. Symptoms include a ticking noise from the front of the engine, rough running, loss of power, and on higher-mileage examples, chain stretch requiring replacement.
Repair vs replace:
Timing chain and tensioner replacement is a significant job - the front of the engine must be dismantled, typically costing £800-£1,500. If the chain has slipped and valves have contacted pistons, a full replacement engine is the only safe option. Read our full /failures/timing-chain-failure guide
Read more about this issue
3. CCV (Crankcase Ventilation) System Blockage
3. CCV (Crankcase Ventilation) System Blockage
Typical onset:
70,000-120,000 miles
What happens:
The N46's crankcase ventilation system (CCV) can become completely clogged with sludge, particularly on vehicles with high mileage or infrequent oil changes. A blocked CCV increases crankcase pressure, leading to oil leaks, increased oil consumption, and rough idle.
Repair vs replace:
CCV replacement is a moderate-cost repair (£300-£500) that can resolve oil consumption and idle issues. Often performed alongside valve stem seal replacement as part of a comprehensive engine service.
Read more about this issue
The N46 was updated in 2007 to the N46N specification, featuring changes to the intake manifold, exhaust camshaft and engine control unit (from Bosch ME9.2 to MV17.4.6). Later N46 engines (2007-2015) benefit from improved engine management and valvetrain components. The N46 is generally considered more reliable than the N42 it replaced, though the valve stem seal and timing chain issues persist across the entire production run.
Compare rebuilt N46B20 prices with the failure already addressed
Engine Variants
How to Confirm You Have the N46B20
The N46B20 is a Specific engine code covering BMW's 2.0-litre valvetronic four-cylinder. Unlike Family pages that cover multiple fundamentally different engines, this page covers the N46B20 as a single engine with multiple output tunes and revisions. Where to find your engine code: The engine code is stamped on a machined pad on the engine block - the exact location varies by chassis, but it is typically visible from the driver's side of the engine bay. It also appears on the V5C registration document under "Engine number" (e.g. N46B20Bxxxxxx). A BMW VIN decoder will also confirm the exact variant from the vehicle's build sheet. Key N46B20 variants: | Variant | Power | Key Difference | Applications | |---|---|---|---| | N46B20 | 129 hp (95 kW) | Base 2.0L, Bosch ME9.2 management | E87 118i, E90 318i (2004-2007) | | N46B20 | 143 hp (105 kW) | Higher tune, 200 Nm torque | E46 318i, 318Ci, 318ti (2004-2005) | | N46B20 | 150 hp (110 kW) | Highest tune, 200 Nm @ 3,600 rpm | E46 318Ci, E84 X1 2.0i, E87 120i | | N46N | 129-150 hp | 2007+ update, Bosch MV17.4.6 management, revised intake/exhaust | E87 LCI, E90 LCI, E84 X1 | Why fitting the wrong variant matters: While all N46B20 variants share the same basic architecture, they have different ECU calibrations, intake manifolds and in some cases camshaft profiles. Fitting a 150 hp engine into a car originally equipped with the 129 hp variant without the corresponding ECU mapping will result in reduced performance and potential drivability issues. Commonly confused codes: | Engine Code | What it is | Why it's confused | |---|---|---| | N42B20 | Predecessor 2.0L engine (2001-2004) | Similar displacement and valvetronic - but N42 has different crankshaft and valvetrain design | | N43B20 | Successor direct-injected 2.0L (2007-2011) | Similar power output but different injection system - not a direct swap | | N45B16 | 1.6L N45 engine without Valvetronic | Smaller displacement, different valvetrain - often confused in 116i models |
Not sure which code you have- Enter your registration above and we'll confirm the exact N46 variant before any quotes are sent.
Easily Confused
N42B20
BMW's first Valvetronic four-cylinder, fitted to the E46 318i and E60 520i from 2001-2004. The N42 had similar displacement but used a different crankshaft design and earlier Valvetronic implementation. The N46 is a significant improvement - with revised valvetrain, updated engine management, and improved oil consumption characteristics (though both engines share the valve stem seal weakness).
Confirm the exact N46B20 fitment
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Buying Guide
Buying a Replacement N46B20 - What to Choose
Choosing the right replacement route depends on your budget, risk tolerance, and ownership goals. Here's a breakdown of your options.
Used:
A used N46B20 can be a cost-effective option for lower-value host vehicles (sub-£3,000 E87 118i, E90 318i) - but only if the engine comes with documented proof of valve stem seal replacement and timing chain/tensioner work. Without this documentation, a used engine is a gamble - oil consumption and chain issues are not "if" but "when". Used prices from £800-£1,200 reflect this risk. Link once:
Reconditioned:
A properly reconditioned N46B20 is the recommended choice for most owners. A full recon should address the engine's known weak points: new valve stem seals (upgraded materials), new timing chain, tensioner and guides, new water pump and thermostat, full gasket set, and CCV system replacement. Given the £1,500-£2,500 supply cost and the host vehicle value (£1,500-£8,000 for a decent E87/E90), this represents a significant but justifiable investment for a well-maintained example. A 12-24 month warranty is essential. Link once:
Rebuilt:
A full N46B20 rebuild is justified for low-mileage, well-maintained examples or where the owner plans long-term ownership. An upgraded rebuild should include forged pistons, upgraded rod bearings and a strengthened timing chain tensioner. Rebuild costs (£2,500-£4,000+) are significant - only consider this for high-value or sentimental vehicles. Link once:
Supply & Fit Line:
All supply options can be fitted through our network of vetted BMW specialists nationwide, with a minimum 12-month warranty on reconditioned and rebuilt units and full nationwide delivery coverage. Link once:
Vehicle Value Note:
The N46B20 sits in ageing host vehicles: E87 118i/120i (£1,500-£5,000), E90 318i/320i (£1,500-£6,000), E60 520i (£1,500-£4,500), E84 X1 sDrive18i (£2,000-£7,000), and E83 X3 xDrive20i (£2,000-£5,000) [THIRD-PARTY - AutoTrader UK market data 2025]. A £1,500-£2,500 reconditioned unit represents 25-80%+ of the vehicle's value on many examples - on a £2,000 E87 118i, a £2,000 replacement is 100% of the vehicle's value, making it a borderline or non-viable decision. The honest marketplace-neutrality position is: if your N46B20 has suffered catastrophic failure (jumped timing, bottom-end damage) and your vehicle is worth under £2,500, evaluate scrap or part-exchange value before committing to a replacement. For well-maintained, low-mileage examples with good bodywork and service history, the replacement can be a worthwhile investment.
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FAQ
BMW N46B20Frequently Asked Questions
Question 1How much does a BMW N46B20 engine replacement cost in the UK-
A reconditioned N46B20 supply-only typically costs between £1,500 and £2,500, with fitted prices ranging from £1,900 to £3,000 depending on labour and additional parts. Used units start from £800 supply-only, while full rebuilds run £2,500-£4,000. All pricing is based on Motorinsul UK and specialist workshop data. Prices vary significantly by variant - N46N (2007+) may command a premium. Supply-only excludes fitting; add 8-12 hours at £65-£91/hr for specialist installation. Always compare quotes - prices can vary by 20% between specialists.
- Prices vary significantly by variant - N46N (2007+) may command a premium.
- Supply-only excludes fitting; add 8-12 hours at £65-£91/hr for specialist installation.
- Always compare quotes - prices can vary by 20% between specialists.
Question 2What is the most common failure on the BMW N46B20-
Valve stem seal wear is the most common issue on the N46B20, causing excessive oil consumption and blue smoke on startup, typically appearing at 60,000-120,000 miles. Timing chain tensioner failure and guide wear are also common, leading to rattling noises and potential timing chain slip. The CCV (crankcase ventilation) system can become blocked, causing oil leaks and rough idle. Valve stem seal replacement is the most frequent repair, typically £1,000-£1,700. Timing chain/tensioner replacement is recommended around 80,000-120,000 miles. Regular oil changes with BMW LL-01 approved oil are critical to longevity.
- Valve stem seal replacement is the most frequent repair, typically £1,000-£1,700.
- Timing chain/tensioner replacement is recommended around 80,000-120,000 miles.
- Regular oil changes with BMW LL-01 approved oil are critical to longevity.
Question 3Which BMW models use the N46B20 engine-
The N46B20 is fitted across multiple BMW platforms from 2004 to 2015: E81/E87 1 Series (118i, 120i), E46 3 Series (318i, 318Ci, 318ti), E90/E91 3 Series (318i, 320i), E60/E61 5 Series (520i), E84 X1 (sDrive18i, sDrive20i), E83 X3 (xDrive20i), and E85/E86 Z4 (Z4 2.0i). The engine appears in multiple power outputs: 129 hp, 143 hp, and 150 hp. Check your V5C or engine block stamp to confirm your exact variant. The N46 is BMW-exclusive - no cross-brand sharing.
- The engine appears in multiple power outputs: 129 hp, 143 hp, and 150 hp.
- Check your V5C or engine block stamp to confirm your exact variant.
- The N46 is BMW-exclusive - no cross-brand sharing.
Question 4Should I buy a used, reconditioned, or rebuilt N46B20-
For most N46B20 owners, a reconditioned unit with new valve stem seals and timing chain components is the recommended choice - it addresses the engine's key weaknesses and comes with a 12-24 month warranty. Used units (£800-£1,200) are cheaper but carry high risk without documented valve stem seal and timing chain work. Rebuilds (£2,500-£4,000+) are only justified for low-mileage, high-value examples or sentimental vehicles. Used: only with documented valve stem seal replacement and timing chain/tensioner work. Reconditioned: best balance - all common weak points addressed, warranty included. Rebuilt: ideal for low-mileage, well-maintained examples or long-term keepers.
- Used: only with documented valve stem seal replacement and timing chain/tensioner work.
- Reconditioned: best balance - all common weak points addressed, warranty included.
- Rebuilt: ideal for low-mileage, well-maintained examples or long-term keepers.
Question 5How do I know which N46B20 variant I have (N46B20, N46B20B, N46B20U1, N46B20U2, or N46N)-
The engine code is stamped on a machined pad on the engine block and appears on the V5C under 'Engine number' - the code will read N46B20xxxxxx, N46B20Bxxxxxx, N46B20U1xxxxxx, N46B20U2xxxxxx, or N46Nxxxxxx. Use a BMW VIN decoder to confirm from the build sheet. The N46N (2007+) features Bosch MV17.4.6 engine management and revised intake/exhaust components. N46B20 = 129 hp (base) / 143 hp / 150 hp depending on tune (2004-2007). N46B20B = N46N variant, 150 hp (2007-2015). N46B20U1/U2 = lower-output variants, 129-143 hp. Fitting the wrong ECU variant requires specialist coding.
- N46B20 = 129 hp (base) / 143 hp / 150 hp depending on tune (2004-2007).
- N46B20B = N46N variant, 150 hp (2007-2015).
- N46B20U1/U2 = lower-output variants, 129-143 hp.
- Fitting the wrong ECU variant requires specialist coding.
Question 6Is the N46B20 reliable, and what mileage can I expect-
The N46B20 is a reasonably reliable engine for a modern BMW four-cylinder - with diligent maintenance (10,000-mile oil changes, BMW LL-01 approved oil), many owners report 120,000-150,000+ miles before needing major work. The key is addressing the valve stem seals and timing chain tensioner proactively before they cause more extensive damage. Budget for valve stem seal replacement around 80,000-100,000 miles as preventative maintenance. Replace timing chain tensioner at 80,000-120,000 miles. Regular oil changes and avoiding short journeys help prevent CCV blockages. Full service history is essential - this engine rewards careful maintenance.
- Budget for valve stem seal replacement around 80,000-100,000 miles as preventative maintenance.
- Replace timing chain tensioner at 80,000-120,000 miles.
- Regular oil changes and avoiding short journeys help prevent CCV blockages.
- Full service history is essential - this engine rewards careful maintenance.
Compare BMW N46B20 Engine Prices Today
Get free, no-obligation comparison quotes for your N46B20 from our curated network of UK BMW four-cylinder specialists. Every quote is specific to your exact engine code and variant, and our reg-lookup tool confirms fitment before any specialist reaches out. With reconditioned N46B20 units from £1,500 (estimated), comparing takes two minutes and could save hundreds on your replacement - but always weigh the cost against your vehicle's current market value before committing.
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