How much does a Jaguar XK 4.0 engine replacement cost in the UK?

A reconditioned XK 4.0 engine typically costs £3,000–£6,000 supply only depending on variant. Fitting adds £1,500–£2,500 depending on location and workshop rates. A full rebuild including all bearings, pistons, valves, springs and timing gear costs approximately £5,000 (£3,000 in parts, £2,000 in labour excl. VAT). Main dealer new engines are no longer available. Use our calculator for a figure specific to your car.

Is the Jaguar XK 4.0 engine reliable?

The 4.0 AJ-V8 is a solid engine with a good reputation if properly maintained. However, it has two well-documented weaknesses: (1) plastic timing chain tensioners that can fail and destroy the engine, and (2) Nikasil cylinder liners on pre-1999 engines that could fail due to high sulphur fuel. Upgrading to metal tensioners and confirming Nikasil health are essential. The 4.2-litre engine introduced in 2003 resolved both issues.

What are the common problems with the Jaguar XK 4.0?

The main known issues are: (1) Plastic timing chain tensioner failure - the most critical weakness, causing cold-start rattle and risk of catastrophic engine damage, (2) Nikasil cylinder liner failure on pre-1999 engines - causing loss of compression, (3) Cooling system failures - plastic water pump, crossover pipe and thermostat housing, and (4) Supercharger coupler wear on XKR models.

Is it worth replacing a Jaguar XK 4.0 engine, or should I scrap the car?

Depends on vehicle value and condition. Against a well-kept £6,000–£15,000 XK, a £3,000–£5,000 recon is 20–80% of the car's value. For a clean example with good body and no rust, replacement is often worth it given the XK's rising classic status. However, if the car has other issues (convertible top, transmission, rust), evaluate total restoration costs before committing.

How do I find my Jaguar XK 4.0 engine code?

The XK 4.0 uses the AJ26 (naturally aspirated) or AJ27S (supercharged) engine codes. The XK8 has the naturally aspirated 4.0 (AJ26); the XKR has the supercharged 4.0 (AJ27S). The engine code is stamped on the cylinder block. Tell us your registration and we'll confirm it for free.

Can I replace the plastic timing chain tensioners, or does it need engine replacement?

Yes - the plastic tensioners can be replaced with upgraded metal tensioners without removing the engine. A preventative replacement of the upper tensioners costs under £250 as a DIY. This is the single most important maintenance item on any 4.0 XK. At the first sign of rattling, book an inspection immediately. If the tensioner fails and the chain snaps, a full engine replacement is usually the only option.

Jaguar XK 4.01996–20052 Engine Variants (AJ26 & AJ27S)

Jaguar XK 4.0 Engine Replacement - Compare Prices & Get Quotes

Name: Jaguar XK 4.0 UK Engine Enquiry Data 2025
Creator: JaguarEngine.uk

Get quotes today from trusted UK Jaguar XK specialists. The 4.0-litre AJ-V8 powers the first-generation XK8 and XKR - compare reconditioned, rebuilt and used engines with supply & fit available nationwide.

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Jaguar XK 4.0 Engines - from £800 to £8,000Engine codes: AJ26, AJ27, AJ27S

Jaguar XK 4.0 Engines - from £800 to £8,000· Engine codes: AJ26, AJ27, AJ27S

Instant QuotesNo Obligation100% FreeReconditionedRebuiltUsedSupply & Fit AvailableUK-Wide NetworkInstant QuotesNo Obligation100% FreeReconditionedRebuiltUsedSupply & Fit AvailableUK-Wide Network

Jaguar XK 4.0 Which Engine Does Your Car Actually Have?

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

Era Note

4.0L naturally aspirated V8 - 284–294 hp. Nikasil liners (pre-1999) and plastic tensioners are the key risks

GenerationYearsEngine CodeReliabilityRecon CostEra Note

1996–2005AJ26★★★☆☆ [NEWLY ASSIGNED - see Data Note]£3,000–£6,000 [JAG-QUOTE]4.0L naturally aspirated V8 - 284–294 hp. Nikasil liners (pre-1999) and plastic tensioners are the key risks

1997–2003AJ27S★★★☆☆ [NEWLY ASSIGNED - see Data Note]£3,500–£8,000 [JAG-QUOTE]4.0L supercharged V8 - 360–370 hp. Same block; plastic tensioners and Eaton M112 supercharger are weak points

Why use this era map?

Every cost guide, reliability rating and engine code on this page is aligned to the data above. This keeps everything consistent and trustworthy.

Real UK Cost Data

Verified Reliability

Expert Insights

Updated for 2025

Jaguar XK 4.0 Engine Replacement Costs

Supply Only£3,000–£6,000

Fitted (Indie)£4,500–£8,000

Warranty12–24 months

Best ForMost owners - best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£800–£2,500£1,500–£4,0001–6 monthsBudget priority; donor for rebuild

Reconditioned Engine£3,000–£6,000£4,500–£8,00012–24 monthsMost owners - best cost/warranty balance

Rebuilt Engine£4,500–£8,000£6,000–£10,00012–24 monthsLong-term ownership; 3+ year horizon

Main Dealer NewN/AN/AN/ANo longer manufactured

Labour estimate: Fitting an XK 4.0 engine typically takes 14–18 hours at £65–£95/hr (independent) or £110–£160/hr (London/SE dealer). Timing chain tensioner replacement is a critical preventative job costing £250–£500 in parts and labour.

Compare XK 4.0 engine prices from UK specialists

Common Problems

1. Plastic Timing Chain Tensioner Failure (The Achilles Heel)

Symptoms: Rattling or ticking noise from the engine on cold start, especially from the top of the engine; metallic noise that subsides as oil pressure builds; sudden engine failure if tensioner breaks

Typical mileage: 50,000–80,000 miles - can fail without warning

Repair cost: £250–£500 (preventative upper tensioner replacement - DIY possible) / £1,500–£3,000 (full timing chain kit)

Replacement cost: £4,500–£10,000 (if chain snaps - full engine replacement)

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

Our recommendation:

The plastic-bodied upper timing chain tensioners are the "major achilles heel" of the 4.0 AJ-V8. Pre-2003 engines have four timing chains and four plastic tensioners that can break up over time. If a tensioner fails, the chain can snap and destroy the engine. The top "secondary" tensioners (which tension the short chain between the two camshafts) are the most at risk. A preventative replacement of the upper tensioners costs under £250 as a DIY using an upgraded metal tensioner kit. At the first sign of rattling, get the tensioners inspected immediately - this is the single most important maintenance item on any 4.0 XK.

Read the full timing chain tensioner guide → /failures/aj-v8-timing-chain-tensioners/ [NEW FAILURE PAGE NEEDED]

1. Plastic Timing Chain Tensioner Failure (The Achilles Heel)

Typical mileage: 50,000–80,000 miles - can fail without warning

Repair cost: £250–£500 (preventative upper tensioner replacement - DIY possible) / £1,500–£3,000 (full timing chain kit)

Replacement cost: £4,500–£10,000 (if chain snaps - full engine replacement)

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

Our recommendation:

Read the full timing chain tensioner guide → /failures/aj-v8-timing-chain-tensioners/ [NEW FAILURE PAGE NEEDED]

2. Nikasil Cylinder Liner Failure (Pre-1999 Engines)

Symptoms: Loss of compression, rough running, misfires, increased oil consumption, hard starting, failed emissions test

Typical mileage: 40,000–100,000 miles - affected by high sulphur fuel

Repair cost: £3,000–£6,000 (engine rebuild with new liners) / £4,500–£10,000 (engine replacement)

Replacement cost: N/A - repair or replacement required

🟠 Check - have a compression test performed; if low readings, book inspection urgently

Our recommendation:

Early AJ26 engines (pre-1999) used Nikasil-coated cylinder bores. In the late 1990s, low-quality fuel with high sulphur content caused the Nikasil lining to erode, leading to loss of compression and engine failure. By the end of 1999, Jaguar replaced Nikasil with more reliable cast-iron sleeves. If you're considering a pre-1999 XK, have a compression test performed. Most Nikasil engines that are still running today have survived the issue, but it's worth confirming with a specialist.

Read the full Nikasil failure guide → /failures/nikasil-cylinder-liner-failure/ [NEW FAILURE PAGE NEEDED]

3. Cooling System Failures (Water Pump & Crossover Pipe)

Symptoms: Coolant loss, overheating, steam from engine bay, temperature gauge rising, heater blowing cold

Typical mileage: 60,000–100,000 miles - plastic components age and fail

Repair cost: £300–£800 (water pump, thermostat, crossover pipe)

Replacement cost: N/A - repair only (does not progress to engine replacement if addressed)

🟠 Check - book inspection urgently if temperature rises

Our recommendation:

The 4.0 V8 has a "plastic water pump" as a known failure point. The coolant crossover pipe is another common failure, along with ageing hoses and the thermostat housing. Cooling system failures are a "primary weakness" that can cause "premature engine failure if neglected". Preventative replacement of the water pump, crossover pipe and thermostat at 60,000–80,000 miles is strongly recommended. If the temperature gauge rises, shut the engine down immediately - overheating an aluminium V8 can cause catastrophic damage.

Read the full cooling system failure guide

4. Supercharger Coupler Wear (XKR, AJ27S)

Symptoms: Rattling or clattering noise from the supercharger at idle, reduced boost, loss of power, poor throttle response

Typical mileage: 60,000–100,000 miles - the Eaton M112 coupler wears over time

Repair cost: £300–£800 (supercharger coupler replacement)

Replacement cost: N/A - repair only (does not progress to engine replacement if addressed)

🟡 Monitor - book inspection if rattling develops

Our recommendation:

The supercharged AJ27S engine in the XKR uses an Eaton M112 supercharger. The supercharger coupler - a small plastic/nylon component that connects the supercharger rotor to the drive pulley - can wear over time, causing a rattling noise at idle. If you hear rattling from the supercharger, have the coupler inspected. Replacement is a straightforward specialist job that restores full supercharger performance.

Read the full supercharger coupler guide → /failures/supercharger-coupler-wear/ [NEW FAILURE PAGE NEEDED]

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XK 4.0 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.

XK 4.0 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 SensePlastic tensioner rattle (early detection)✅ Yes£250–£500Preventative - upgraded metal tensioners eliminate the riskTiming chain snapped❌ Usually NoEngine replacementInterference engine - piston-valve contact means full rebuild or replacementNikasil liner failure (pre-1999)⚠️ Sometimes£3,000–£6,000Engine rebuild with new liners or replacement requiredCooling system failure✅ Yes£300–£800Preventative replacement recommended at 60k–80k milesSupercharger coupler wear (XKR)✅ Yes£300–£800Straightforward component replacement

Buying This XK 4.0? Check These First

Buy If

Post-1999 engine with cast-iron liners (Nikasil issue resolved)
Documented timing chain tensioner replacement with upgraded metal parts - this is the critical item
Full service history with regular oil changes
Cooling system overhaul completed (water pump, crossover pipe, thermostat)

Avoid If

Pre-1999 engine with no Nikasil test or documentation
Rattling or ticking from the top of the engine - tensioner warning
Overheating history or cooling system issues - the aluminium V8 is unforgiving of overheating
Poor service history - the 4.0 V8 is a solid engine but needs proper maintenance

Closing Verdict

The Jaguar XK 4.0's AJ-V8 is a landmark engine - Jaguar's first production V8. It delivers a glorious soundtrack and effortless performance, with up to 294 hp in naturally aspirated form and 370 hp in the supercharged XKR. The engine has a solid reputation if properly maintained, but the plastic timing chain tensioners are the critical weak point - they must be replaced with upgraded metal versions as a matter of urgency. Pre-1999 Nikasil liners are also a concern. Buy a well-maintained example with documented tensioner work and cooling system history. Without history? The repair bills can be substantial.

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

Compare XK 4.0 engine prices before you buy

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Buying Checklist

Before you buy a used Jaguar XK 4.0 (or before you commit to an engine replacement), check these:

Cold Start

Listen for rattling or ticking from the top of the engine (tensioner warning - this is critical)

Tensioner History

Have the plastic tensioners been replaced with upgraded metal parts? This is the single most important question

Nikasil Check

Pre-1999 cars need a compression test to confirm liner health

Service History

Including the AJ26/AJ27S engine and confirmed oil change intervals

Cooling System

Check for coolant leaks; ask about water pump, crossover pipe and thermostat history

Supercharger Noise

Any rattling at idle? (XKR models - coupler wear)

Engine Warning Light

Have codes been read? Look for misfire or timing-related codes

MOT History

Check for emissions-related failures

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.

Engine Codes

This table's rows match Section 1B's Era Map exactly.

AJ26 (4.0 NA)

Years1996–2005

Power284–294 hp (209–216 kW) / 393 Nm

2025 Enquiries- (pattern data)

Avg. Recon Cost£3,000–£6,000【JAG-QUOTE】

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

AJ26 (4.0 NA)1996–2005284–294 hp (209–216 kW) / 393 Nm- (pattern data)£3,000–£6,000【JAG-QUOTE】

AJ27S (4.0 SC)1997–2003360–370 hp (265–272 kW) / 505–525 Nm- (pattern data)£3,500–£8,000【JAG-QUOTE】

Technical Specs

AJ27S 4.0 Supercharged

Displacement3,996 cc (4.0L)

Cylinders8-cylinder V

Bore86.1 mm / Stroke: 86.1 mm

Cylinder BlockAluminium V8 (Nikasil pre-1999 / cast-iron sleeves post-1999)

Cylinder HeadAluminium 32-valve DOHC

ValvetrainDOHC, 4 valves per cylinder, chain-driven

Compression Ratio9.0:1

Fuel SystemDistributed injection

Power284–294 hp (209–216 kW)

Torque393 Nm

0-60 mph6.3 seconds (XK8)

Top Speed155 mph (XK8)

Displacement3,996 cc (4.0L)

Cylinders8-cylinder V

Cylinder BlockAluminium V8

ValvetrainDOHC, 4 valves per cylinder, chain-driven

Compression Ratio8.9:1

SuperchargerEaton M112

Power360–370 hp (265–272 kW)

Torque505–525 Nm

0-60 mph5.2 seconds (XKR)

Top Speed174 mph (XKR)

Engine Oil5W-30, 7.3 litres (AJ27S)

→ Compare XK 4.0 engine prices for your Jaguar

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Market Intelligence

Most Common Failure

Plastic timing chain tensioner failure

the "major achilles heel" of the 4.0 AJ-V8

Average Enquiry Mileage

50,000

–80,000 miles【PATTERN DATA】

Average Replacement Cost

£4,000

reconditioned, supply only【JAG-QUOTE】

Most Requested Engine Code

AJ26 (naturally aspirated)【PATTERN DATA】

Peak Enquiry Season

Spring / Summer

classic car season【PATTERN DATA】

Regional Demand

South East18%

London15%

South West (10%)【PATTERN DATA】

Regional Demand Breakdown

18%South East

15%London

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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