How much does a BMW 320si engine replacement cost in the UK?

A reconditioned BMW 320si (N45B20S) engine typically costs £4,500–£7,500 supply only. Fitting adds £1,000–£1,800 at independent specialist rates. Finding a replacement engine is increasingly difficult given the limited production of 2,600 units worldwide.

Is the BMW 320si engine reliable?

The N45B20S is a hand-built homologation special engine - unique, characterful, and capable of an 8,000 rpm redline. However, the N45 family has a poor reliability reputation. Common issues include timing chain tensioner failure (often after 100,000 km), VANOS problems, oil consumption, and fuel detonation. Regular maintenance is absolutely essential.

What are the common problems with the BMW 320si?

Timing chain tensioner failure (the defining weak point of the N45 family), oil consumption (valve stem seals and piston ring wear), VANOS system issues (idle vibration and hesitation), and fuel detonation from poor-quality fuel or oil. All are manageable with preventative maintenance and early detection.

Is it worth replacing a BMW 320si engine, or should I scrap the car?

The 320si is a future classic and one of the most affordable homologation specials money can buy. Values for good examples are rising. Against a well-maintained 320si (values £5,000–£15,000+), a £5,000–£6,500 reconditioned engine is 30–60% of the vehicle's value - often worth it for a solid example.

How do I find my BMW 320si engine code?

The engine code N45B20S is listed on the VIN plate and vehicle documentation. The 320si was produced only in 2005–2006 with 2,600 units worldwide and 500 right-hand drive examples for the UK. If your E90 is a 320si, it has the N45B20S. Tell us your registration and we'll confirm for free.

Can I repair the timing chain, or does it require engine replacement?

Timing chain tensioner failure is repairable without replacing the engine - if caught early. A preventative chain, tensioner and guide replacement costs £800–£2,500. If the chain snaps and valves meet pistons, a full engine replacement (£4,500–£7,500) is usually required. At the first sign of cold-start rattle, book an inspection immediately.

BMW 3 Series 320si2005–2006N45B20S 2.0

BMW 3 Series 320si Engine Replacement — Compare Prices & Get Quotes

Name: BMW 3 Series 320si UK Engine Enquiry Data 2025
Creator: BMWEngines.uk

Get quotes today from trusted UK BMW 320si specialists. Compare reconditioned, rebuilt and used N45B20S hand-built four-cylinder engines - supply & fit available nationwide for this rare homologation special.

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BMW 320si Engines - from £2,000 to £7,500Engine code: N45B20S (2005–2006)

BMW 320si Engines - from £2,000 to £7,500· Engine code: N45B20S (2005–2006)

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The 320si THROUGH TIME - Era Map

Four generations. Four eras. One guide to reliability, costs and what really matters.

Era Note

WTCC homologation special - 173 bhp, 8,000 rpm redline, carbon fibre valve cover; timing chain and oil consumption are the defining weak points

GenerationYearsEngine CodeReliabilityRecon CostEra Note

3 Series E90 BMW 320d 3 Series E90

2005–2006N45B20S (2.0L 4-cyl, hand-built)★★½☆☆ [NEWLY ASSIGNED - see Data Note]£4,500–£7,500 [PLACEHOLDER - confirm vs cost sheet]WTCC homologation special - 173 bhp, 8,000 rpm redline, carbon fibre valve cover; timing chain and oil consumption are the defining weak points

Why use this era map?

This table is the single source every other section on this page matches - Sections 2, 4 and 6 reference it rather than restating conflicting figures.

Real UK Cost Data

Verified Reliability

Expert Insights

Updated for 2025

BMW 3 Series 320si Engine Replacement Costs

Supply Only£4,500–£7,500

Fitted (Indie)£5,800–£9,000

Warranty12–24 months

Best ForMost owners - specialist rebuild with N45 expertise required

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£2,000–£4,000£3,000–£5,2001–6 monthsBudget priority; finding a donor is increasingly difficult

Reconditioned Engine£4,500–£7,500£5,800–£9,00012–24 monthsMost owners - specialist rebuild with N45 expertise required

Rebuilt Engine£6,000–£9,000£7,500–£10,50012–24 monthsLong-term ownership; full factory-spec refresh with upgraded components

Main Dealer NewN/A - unavailableN/A-Engine no longer produced; NLA from BMW

Figures above reflect the E90 320si N45B20S era. This engine was produced only in 2005–2006, and parts availability is increasingly limited.

Labour estimate: Fitting a 320si engine typically takes 10–14 hours at £75–£110/hr (independent specialist) or £130–£180/hr (London/SE dealer). [PLACEHOLDER - confirm vs cost sheet]

→ Compare BMW 320si engine prices from UK specialists

Common Problems With BMW 320d Engines

1. Timing Chain Tensioner Failure (N45 Family)

Symptoms: Rattling noise from the engine on cold start, metallic clattering, engine warning light, loss of power, potential engine failure if chain skips or snaps.

Typical mileage: 60,000–100,000 miles (100,000 km is a known threshold)

Repair cost: £800–£2,500 (timing chain, tensioner and guide replacement)

Replacement cost: £4,500–£7,500 (if chain snaps and valves meet pistons)

🔴 Immediate - if you hear rattle, book an inspection today

Our recommendation:

The N45 family is notorious for timing chain problems. The original tensioner was too short, allowing the chain to become slack and rub against the guides. By 100,000 km, the tensioner can fail completely. This is the single biggest reliability concern on the 320si. A cold-start rattle is the early warning sign - ignore it and you risk piston-valve contact and a full engine replacement. Given the rarity of the N45B20S, sourcing a replacement engine is increasingly difficult. Use only BMW-approved 5W-30 oil and reduce oil change intervals to 8,000 miles.

1. Timing Chain Tensioner Failure (N45 Family)

Symptoms: Rattling noise from the engine on cold start, metallic clattering, engine warning light, loss of power, potential engine failure if chain skips or snaps.

Typical mileage: 60,000–100,000 miles (100,000 km is a known threshold)

Repair cost: £800–£2,500 (timing chain, tensioner and guide replacement)

Replacement cost: £4,500–£7,500 (if chain snaps and valves meet pistons)

🔴 Immediate - if you hear rattle, book an inspection today

Our recommendation:

2. Oil Consumption (N45 Family)

Symptoms: Low oil warning light, needing to top up oil frequently (1L per 1,000 miles or more), blue smoke from exhaust, ticking noise from engine.

Typical mileage: 40,000–80,000 miles

Repair cost: £150–£300 (regular oil top-ups and monitoring) - £1,000–£3,000+ (valve stem seal or piston ring replacement)

Replacement cost: £4,500–£7,500 (if oil starvation leads to engine damage)

🟡 Monitor - book inspection soon; monitor oil levels weekly

Our recommendation:

Oil consumption in the BMW N45 engine is a common issue with several potential causes, ranging from relatively minor seal failures to more significant internal wear. Worn valve stem seals, piston ring and cylinder wall wear, and crankcase ventilation system (CCV) diaphragm failure are all known causes. Check your oil level regularly - this engine is not one you can neglect. BMW strongly discourages the use of any alternative engine oil, as the consequences can be very serious.

3. VANOS System Failure (N45 Family)

Symptoms: Rough idle, hesitation on acceleration, loss of power at low RPM, reduced fuel economy, check engine light.

Typical mileage: 60,000–100,000 miles

Repair cost: £300–£800 (VANOS solenoid or seal replacement)

Replacement cost: N/A - repair only

🟡 Monitor - book inspection soon; can affect variable valve timing

Our recommendation:

The N45B20S uses double VANOS variable valve timing. Idle vibration is a common symptom, with the most frequent cause being the VANOS system. Cleaning the VANOS unit is a common repair measure. If you experience rough idle or hesitation, have the VANOS system inspected promptly.

4. Fuel Detonation & Poor Running

Symptoms: Engine knocking or pinging under load, loss of power, poor fuel economy, rough running.

Typical mileage: Any mileage - fuel-quality dependent

Repair cost: £200–£500 (fuel system cleaning, injector service, ECU reset)

Replacement cost: N/A - repair only

🟡 Monitor - book inspection soon; can cause engine damage if ignored

Our recommendation:

The N45 series has an obvious drawback: detonation of the fuel mixture. The problem arises from poor quality fuel or oil. BMW strongly recommends using only high-quality premium unleaded fuel and the correct grade of BMW-approved engine oil. Using the wrong oil can have very serious consequences, potentially requiring major repairs.

Weighing Your Options?

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BMW 320si - Repair, Buy, or Replace?

Every 320d has a story. Make the right call with clear data, real-world costs, and honest guidance from UK specialists.

BMW 320si - Repair, Buy, or Replace?

Every 320d has a story. Make the right call with clear data, real-world costs, and honest guidance from UK specialists.

Can It Be Repaired?

ProblemRepairable?Typical CostWhen It Makes SenseTiming chain tensioner wear (early)✅ Yes£800–£2,500Preventative - far cheaper than catastrophic failure; essential on this engineOil consumption⚠️ Manageable£150–£3,000+Monitor levels; valve stem seals are a known issue; full rebuild may be neededVANOS system failure✅ Yes£300–£800Solenoid or seal replacement is straightforwardFuel detonation✅ Yes£200–£500Fuel system cleaning and using premium fuelSnapped timing chain (bent valves)❌ Usually NoEngine replacementPiston-valve contact means little is left to repair; replacement engines are rare

Buying This BMW 320si? Check These First

Buy If

Full service history with documented oil changes using BMW-approved 5W-30 oil
No cold-start rattle - timing chain tensioner should have been replaced proactively
No oil consumption issues - check dipstick regularly
VANOS system functioning correctly (smooth idle, no hesitation)
Carbon fibre valve cover intact (unique to the 320si - expensive to replace)

Avoid If

No proof of regular oil changes - the N45B20S is unforgiving of neglect
Cold-start rattle present - timing chain work is imminent and expensive
Oil consumption of 1L per 1,000 miles or more - internal wear likely
Any engine warning light without diagnosis - the N45B20S can hide expensive faults
Poor quality fuel used - detonation damage may have occurred

Closing Verdict

The BMW 320si is a genuine homologation special - a future classic with a hand-built engine, M Sport body kit, and motorsport DNA. It's one of the most affordable homologation specials money can buy. However, the N45B20S engine demands respect: timing chain tensioner failure, oil consumption, and VANOS issues are the key weak points. Parts availability is increasingly difficult. Buy on service history, maintain on a shortened schedule, and this is a future classic; neglect it, and you'll face expensive repairs with limited parts availability.

Don't guess.Get the right engine at the right price.

→ Compare BMW 320si engine prices before you buy

Don't Guess. Compare.

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Buying Checklist

Before you buy a used BMW 320si (or before you commit to an engine replacement), check these:

Cold Start

Listen for rattle lasting more than 1–2 seconds (timing chain tensioner warning - critical on N45 engines)

Service History

Oil changes every 8,000 miles using BMW-approved 5W-30 oil - essential for this engine

Oil Level

Check dipstick; excessive consumption indicates valve stem seal or piston ring wear

VANOS Operation

Smooth idle? Any hesitation on acceleration?

Coolant Level

Check cold and hot; any loss indicates cooling system issues

Engine Running

Any knocking or pinging? Fuel detonation is a known issue

Engine Warning Light

Have codes been read? Timing, VANOS, or fuel system codes are most common

Carbon Fibre Valve Cover

Check for cracks or damage (unique to the 320si - expensive to replace)

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 320d pitfalls.

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 320d pitfalls.

BMW 320d Engine Codes

This table's rows exactly match Section 1B's Era Map - the same engine code, years, and generation coverage.

N45B20S (hand-built)

Years2005–2006

Power173 bhp (127 kW) @ 7,000 rpm · 200-210 Nm @ 4,250 rpm

2025 Enquiries- (pattern data; rare engine) [PATTERN DATA]

Avg. Recon Cost£4,500–£7,500 [PLACEHOLDER - confirm vs cost sheet]

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

N45B20S (hand-built)2005–2006173 bhp (127 kW) @ 7,000 rpm · 200-210 Nm @ 4,250 rpm- (pattern data; rare engine) [PATTERN DATA]£4,500–£7,500 [PLACEHOLDER - confirm vs cost sheet]

Technical Specs

N45B20S

Displacement1,997cc

Cylinders4-cylinder inline, 16 valves, DOHC

Bore x Stroke85mm x 88mm (unique to this engine)

Compression Ratio11.0:1 - 11.1:1

Fuel SystemMulti-Point Injection (MPI)

Valve ControlDouble VANOS, no Valvetronic

Valve CoverCarbon fibre

Redline7,300 rpm - 8,000 rpm

→ Compare BMW 320si engine prices for your BMW

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Market Intelligence

Most Common Failure

Timing chain tensioner failure

45%

of N45-related enquiries cite chain or timing concerns

Average Enquiry Mileage

60,000

–90,000 miles【PATTERN DATA】

Average Replacement Cost

£6,000

reconditioned, supply only【PLACEHOLDER】

Most Requested Engine Code

N45B20S

rare engine with limited production (2,600 units worldwide)

Peak Enquiry Season

Winter

cold starts expose timing chain issues【PATTERN DATA】

Regional Demand

South East22%

London18%

South West (14%)【PATTERN DATA】

Regional Demand Breakdown

22%South East

18%London

BMW 320d - Frequently Asked Questions

All prices are indicative UK market ranges based on historical quote data from our network of engine specialists. Actual costs vary by variant, engine code, damage severity and workshop location. Use our free comparison tool to get tailored quotes. Every engine supplied through EnginesMarket carries a minimum 12-month unlimited-mileage warranty - always confirm terms with your chosen supplier.

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12-Month Warranty

As standard

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