JAGUAR P36677B Engine Cylinder Head 4.2L

( Manufacturer Part Number: P36677B ), ( Type: Cylinder Head ), ( Vintage Part: Yes ), ( Country Of Origin: United Kingdom ), ( Performance Part: No )

Review JAGUAR Series 4.2l Engine Cylinder Head fits XJ6

The **Jaguar P36677B cylinder head** for the iconic **XJ6 (Series III, 1994 2003)** with its legendary **4.2-liter inline-six engine** represents a masterclass in British automotive engineering, blending performance, reliability, and timeless elegance. Crafted from high-grade cast iron with precision machining, this cylinder head is a critical component that governs the breathing and efficiency of the famed **AHV (Advanced High-Velocity) induction system**, which was a hallmark of Jaguar s mid-1990s engine design. The head features **six individual intake and exhaust ports**, each meticulously contoured to optimize airflow and combustion, ensuring a smooth, linear power delivery that defines the XJ6 s character whether cruising effortlessly at highway speeds or spiriting through tight corners with effortless refinement. The **integrated valve springs, retainers, and hydraulic lifters** work in harmony to maintain precise valve timing, reducing wear while maximizing performance, a hallmark of Jaguar s commitment to durability without sacrificing exhilaration. The **intake manifold ports** are designed to channel air into the combustion chambers with minimal turbulence, while the **exhaust ports** are engineered to efficiently expel spent gases, contributing to the engine s signature growl and the XJ6 s reputation for a voice that commands attention. This cylinder head is also equipped with **individual throttle bodies** (in the case of the carbureted or early fuel-injected variants) or **multi-point fuel injection** (for later models), allowing for precise fuel delivery that enhances throttle response and fuel economy. Whether restored to its original glory or modified for enhanced performance, the **P36677B** remains a cornerstone of the XJ6 s legendary driving experience, embodying the perfect marriage of British craftsmanship and automotive passion. For enthusiasts and mechanics alike, this component is not just a replacement part it s a piece of automotive history that continues to deliver the soul of the XJ6 with every rev.

**Pros and Cons of Buying a Jaguar P36677B XJ6 4.2L Engine Cylinder Head**

The **Jaguar P36677B** cylinder head is associated with the **4.2L AJ6 engine**, a classic inline-six powerplant found in Jaguar XJ6 models from the late 1980s to the early 2000s. Below is a detailed breakdown of its advantages and drawbacks, followed by a conclusion and recommendation.

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### **Pros**

1. **Proven Reliability (When Maintained Properly)**

The AJ6 engine, when kept in good condition, is known for its durability, especially in lower-mileage examples. Many owners report that with regular maintenance such as valve adjustments, timing belt replacements, and oil changes the engine can last well beyond 200,000 miles. The P36677B head itself is a common replacement part, meaning it has been widely tested and used in restorations.

2. **Aftermarket Support and Availability**

The AJ6 engine benefits from a strong aftermarket community. Parts like cylinder heads, gaskets, valves, and springs are readily available, often at reasonable prices. This makes repairs and modifications more accessible compared to some older Jaguar engines. Companies like **Jaguar Performance Parts, ECS, and AJ Performance** produce high-quality replacements.

3. **Potential for Performance Upgrades**

- **Forced induction (turbo/supercharger):** The AJ6 responds well to forced induction, with many examples running reliably at 400 500 hp with proper support (e.g., upgraded internals, fueling, and cooling).

- **High-flow heads:** Aftermarket heads (e.g., **AJ Performance, ECS**) can improve airflow and power, especially when paired with a camshaft upgrade.

- **Ported and polished stock heads:** Even stock heads can see power gains with porting and polishing, though this is more labor-intensive.

- **Nitrous oxide (NOS) kits:** Commonly used for quick power boosts, though long-term use requires careful maintenance.

4. **Classic Jaguar Appeal**

For enthusiasts who appreciate the **XJ6 s timeless design, driving dynamics, and V8/AJ6 hybrid options**, the AJ6 offers a more affordable alternative to the V12. The 4.2L inline-six provides a smooth, torquey experience that many find enjoyable, especially in manual-transmission models.

5. **Cost-Effective Restoration**

Compared to a **V12 or V8 (e.g., AJ127, AJ60)**, the AJ6 is significantly cheaper to restore. A complete rebuild (including head work, camshafts, and internals) can cost **$3,000 $6,000**, whereas a V12 rebuild may exceed **$10,000 **. This makes it an attractive option for those on a budget who still want a Jaguar with character.

6. **Modularity and Swappability**

The AJ6 shares many components with other Jaguar engines (e.g., **AJ26, AJ36**), allowing for parts swapping. For example, a **Jaguar XJ40 3.6L head** can sometimes be adapted, though compatibility varies. This flexibility can reduce costs during repairs.

7. **Good for Daily Driving (With Caution)**

While not as luxurious as a modern Jaguar, the XJ6 with an AJ6 can be a practical daily driver if maintained. The inline-six is smooth at cruising speeds, and with modern fuel injection upgrades (e.g., **Megajet, Haltech**), drivability improves significantly over stock carbureted setups.

---

### **Cons**

1. **High Maintenance Requirements**

- **Valve adjustments every 10,000 15,000 miles** (lifters wear out quickly, leading to poor performance or failure if neglected).

- **Timing belt replacement every 60,000 80,000 miles** (critical; failure can destroy the engine).

- **Oil changes every 3,000 5,000 miles** (thin oil and poor sealing can lead to sludge buildup).

- **Head gasket and water pump replacement** (common issues, especially in high-mileage examples).

If these tasks are skipped, the engine can become a **money pit**.

2. **Poor Fuel Economy**

The stock AJ6 is **thirsty**, especially in carbureted form. Expect **12 15 MPG in a manual** and **10 13 MPG in an automatic**. Even with modern fuel injection upgrades, economy remains **worse than modern engines**. This can be a dealbreaker for daily commuters.

3. **Vibration and NVH Issues**

The inline-six layout means **more vibration than a V6 or V8**, which can be noticeable at higher RPMs. The suspension and chassis of older XJ6s are also **softer than modern standards**, leading to a less refined ride. Road noise and wind noise can be intrusive in some models.

4. **Common Failure Points**

- **Lifter wear:** Causes ticking noises and poor performance if not adjusted.

- **Head gasket leaks:** Often due to overheating or poor maintenance.

- **Water pump failure:** Can lead to overheating and head gasket issues.

- **Rod bearings and crankshaft wear:** High-mileage examples may require a full rebuild.

- **Carburetor issues (pre-1994 models):** Throttle response and idle quality can degrade over time.

5. **Limited Modern Compatibility**

- **OBD-II and emissions compliance:** Older AJ6s (pre-1994) lack modern emissions controls, making them **less practical in some regions** where smog checks are required.

- **Fuel system upgrades needed:** Stock carburetors are unreliable; modern fuel injection (e.g., **Megajet, Haltech**) is often necessary for reliability and performance.

- **Alternator and electrical issues:** Older XJ6s may have **weak alternators and poor wiring**, requiring upgrades for modern electronics.

6. **Resale Value and Market Demand**

The AJ6 is **not a high-demand engine** in the classic car market. While parts are available, finding a **fully restored, low-mileage example** can be challenging. The XJ6 itself is **less desirable than a V12 or V8**, so resale value is modest compared to other Jaguars.

7. **Potential for Hidden Damage**

- **Overheating from failed water pumps or thermostats.**

- **Rod knock from worn bearings (audible on compression test).**

- **Blown head gaskets (check for white smoke, coolant in oil, or oil in coolant).**

- **Distressed block (cracks, warping, or corrosion).**

A **pre-purchase inspection (PPI) is essential**, and a **compression test or leak-down test** should be performed.

8. **Noisy Operation**

The AJ6 is **loud**, especially in carbureted form. Modern fuel injection helps, but it still lacks the **silent refinement** of modern engines. Exhaust notes can be **aggressive**, which may not appeal to those seeking a quiet daily driver.

9. **Limited Modern Tuning Options**

While the AJ6 can be tuned, **forced induction (turbo/supercharger) setups require careful engineering** to prevent reliability issues. Unlike modern engines, the AJ6 **does not handle high boost well without significant internal upgrades** (e.g., forged internals, stronger rods, upgraded fueling). Many high-power AJ6 builds **fail prematurely** if not properly supported.

10. **Chassis and Suspension Limitations**

The **XJ6 s suspension is outdated** by modern standards. The **front coil-spring setup and rear live axle** (in older models) can lead to **poor handling, body roll, and wear**. Upgrading to **coilover suspension or independent rear suspension (IRS)** is common but expensive.

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### **Conclusion**

The **Jaguar P36677B XJ6 4.2L AJ6 cylinder head** is a **capable but demanding** component for enthusiasts who appreciate classic Jaguar engineering. It offers **strong performance potential, aftermarket support, and a cult following**, but it comes with **high maintenance requirements, reliability risks, and practical limitations**.

- **Enthusiasts who enjoy mechanical challenges and restoration projects.**

- **Those prioritizing driving dynamics and character over modern comfort.**

- **Owners who can commit to regular maintenance (valve adjustments, timing belt, oil changes).**

- **People who plan to modify the engine (forced induction, fuel injection upgrades).**

- **Budget-conscious buyers who want a Jaguar without the cost of a V12 or V8.**

- **Casual drivers who want a low-maintenance, reliable daily car.**

- **Those in regions with strict emissions laws (pre-19

Details:

Please review all the photos for overall condition and ask any questions prior to purchase. For sale is this Jaguar XJ6 4.2L S2 Engine Cylinder Head P36677B. Have a Wonderful Day!, ID: 36934. Review the pictures, read , and make sure that this is right part for your vehicle.

part #: p36677b price

• $749.99

specifications cylinderheapar:

• for models: Xj6
• for makes: Jaguar
• mpn: P36677b
• type: Cylinder Head
• vintage part: Yes
• country of origin: United Kingdom
• performance part: No

payments cylinderheapar:

• wallet: Paypal
• other
• credit card: Diners-club

general cylinderheapar:

• condition: Used
• Car Truck Parts Accessories > Engines Engine Parts > Cylinder Heads

returns cylinderheapar:

• paid by: Seller
• policy: Returns Accepted
• time: 30 Days

shipping cylinderheapar:

• service: Economy
• type: Fixed
• transit: 3-9 Days
• class: Economy
• cost: $0.00

seller cylinderheapar:

• city: Snohomish, Washington
• rating: 99.8%
• # reviews: 10056

offer cylinderheapar:

• quantity: 1
• sold: 0
• best offers: True
• options: Ship-to-home
• availability: In Stock
• started: February 2, 2026

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