N42 vs N46: Unravelling BMW's 4-Cylinder Engines

For many BMW enthusiasts and owners, the distinction between the N42 and N46 four-cylinder inline engines can often seem like a subtle one. Both power units have been a staple in various BMW models, particularly in the entry-level 1 Series and 3 Series, providing a blend of performance and efficiency. However, despite their apparent similarities at first glance, the N46 is indeed a direct evolution of its predecessor, the N42, incorporating a series of refinements and updates designed to improve performance, efficiency, and potentially, reliability. Understanding these nuances is crucial for accurate diagnosis, maintenance, and even for making informed purchasing decisions.

The Evolution: From N42 to N46

The N46 engine emerged as the next generation of BMW's 4-cylinder inline engines, succeeding the N42B20. At its core, the 2-litre N46B20 version became the most potent iteration among all N46 engines. While it was developed directly from the N42B20, leading to a superficial resemblance, a closer inspection reveals significant internal modifications. BMW's engineers focused on enhancing various components, ensuring the N46 was more than just a rebadged N42.

Key Distinctions: N42 vs. N46

While the N46 carried over much of the N42's fundamental architecture, several critical components underwent redesign or replacement. These changes, though sometimes minor in isolation, collectively contribute to the N46's distinct characteristics and performance profile. Here are the primary differences:

• Crankshaft: The N46 features a new crankshaft, a fundamental component of the engine's rotating assembly. This update often implies revisions to improve balance, durability, or power delivery characteristics.
• Balance Shafts: A notable addition to the N46 is the inclusion of redesigned balance shafts. These are vital for reducing engine vibrations, especially in four-cylinder configurations, leading to a smoother and more refined driving experience.
• Cylinder Head Cover: The N46 sports a renewed cylinder head cover. While seemingly minor, this can impact sealing, heat dissipation, and the integration of other engine components.
• Intake Manifold: The intake manifold was also renewed in the N46. A revised intake manifold can significantly influence air flow dynamics, directly affecting engine breathing, power output, and torque characteristics across the RPM range.
• Timing Chain Tensioner: The timing chain tensioner was changed in the N46. This is a critical upgrade, as issues with timing chain components, including tensioners, were known concerns in earlier BMW engines. A revised tensioner aims to improve timing chain longevity and reduce noise.
• Generators and Spark Plugs: New generators and spark plugs were introduced with the N46. Upgraded generators ensure more reliable electrical supply, while new spark plugs are typically optimised for improved combustion efficiency and emissions.
• Valvetronic Control Integration: Perhaps one of the more significant electronic updates, the Valvetronic control block was additionally integrated into the Engine Control Unit (ECU) in the N46. This closer integration allows for more precise and responsive control over the variable valve lift system, enhancing both performance and fuel economy.
• Engine Control Unit (ECU): The N46 initially utilised the Bosch ME 9.2 control unit. Later, a significant modernisation in 2007 saw the introduction of the Bosch MV17.4.6 control system, particularly for the updated N46N engines. This change in ECU often signifies advanced control algorithms and improved diagnostic capabilities.

It is also worth noting that the engines produced after the 2007 modernisation are typically denoted by an 'N' in their name, such as N46N, signifying these later revisions including a new intake manifold and exhaust camshaft.

The BMW N46B20 Engine: Specifications and Applications

The N46B20 was a versatile engine, forming the backbone for various BMW 18i and 20i models across different series. It also served as the foundational design for the smaller N46B18 version. Furthermore, it shared design principles and components with related models like the N45B20S and N43B20, highlighting BMW's modular engine development strategy. Production of the N46 series concluded in 2012, making way for the new 4-cylinder turbocharged N13B16 engine, a shift reflecting the automotive industry's move towards forced induction for improved efficiency and power density.

N46 Engine Modifications and Power Outputs

The N46 engine family saw several modifications throughout its production run, each tailored to specific vehicle models or performance targets. These variations resulted in different power and torque outputs:

Common Reliability Concerns with the N46B20

Like any complex mechanical system, the N46B20 engine is not without its common issues. Many of these mirror problems found in its predecessor, the N42, often stemming from similar design characteristics or maintenance habits. Awareness of these potential pitfalls can help owners proactively address them, ensuring the longevity and reliable operation of their BMW.

1. High Oil Consumption

This is arguably the most frequently reported issue with the N46, echoing a common complaint from N42 owners. The primary culprits are often worn valve stem seals, which allow oil to seep into the combustion chambers. If left unaddressed, this can lead to premature wear of piston rings. This problem typically manifests around the 30,000-mile (50,000 km) mark. The biggest contributing factor is the use of low-quality or incorrect motor oil. It is absolutely crucial to use the specific oil recommended by BMW, as using alternatives can accelerate wear and lead to these issues.

2. Vibration Issues

Owners may experience noticeable vibrations from the engine. A common remedy for this problem is a thorough cleaning of the Vanos variable valve timing system. Deposits can build up within the Vanos solenoids or units, impeding their precise operation and leading to uneven running and vibrations. Regular servicing and the use of quality oil can help mitigate this.

3. Engine Noise

Noises, particularly rattling or ticking sounds, are another shared issue with the N42. These are often linked to the timing chain system. The timing chain tensioner can fail or become weak, leading to slack in the timing chain itself. A stretched timing chain is also a possibility. These issues typically become apparent after approximately 60,000 miles (100,000 km) of mileage. Addressing these promptly is vital to prevent more severe engine damage.

Other Common Leaks and Replacements

Beyond the major issues, some components are prone to leakage or failure:

• Valve Cover Gasket: It's common for the valve cover gasket to leak around every 30,000 miles (50,000 km). This is a relatively straightforward replacement but should not be ignored, as oil leaks can cause other problems.
• Vacuum Pump: In some instances, replacement of the vacuum pump may be necessary. A failing vacuum pump can affect braking performance and other vacuum-dependent systems.

To prevent these problems and ensure the longevity of your N46B20 engine, the advice is consistent and clear: always use the high-quality motor oil recommended by BMW specialists, and adhere strictly to the recommended regular maintenance schedule. Proactive examinations and timely addressing of minor issues will significantly reduce the likelihood of facing major malfunctions.

Tuning Your BMW N46B20

For those looking to extract a bit more performance from their N46B20, there are a couple of popular avenues, though it's important to manage expectations for a naturally aspirated four-cylinder engine.

Chip Tuning (ECU Firmware)

The simplest and most common method to gain some extra horsepower from your N46B20 is through aggressive ECU firmware, often referred to as chip tuning or a remap. This involves modifying the engine's software to optimise fuel delivery, ignition timing, and other parameters for increased power. To maximise the efficiency of such an upgrade, pairing it with a cold air intake system and a performance cat-back exhaust system is recommended. These modifications improve engine breathing and exhaust flow, potentially adding an extra 10 HP to the stock output.

Supercharger Kits

For a more substantial power increase, supercharger kits are available on the aftermarket. These forced induction systems can significantly boost the N46B20's output, potentially allowing your engine to produce between 200-230 HP. Manufacturers like ARMA are known to offer such kits. The concept involves installing the supercharger kit onto your N46's stock internals. However, it is crucial to note that such modifications are rather expensive, often costing a significant portion of the vehicle's value. Due to the substantial investment required, many enthusiasts often find it more cost-effective to consider upgrading to a more powerful stock BMW model, such as a BMW M3 E90/E92 or a 335i E90/E92, which come with significantly more power from the factory.

Frequently Asked Questions (FAQs)

Is the BMW N46 a good engine?

The N46 is a capable engine for its class, offering reasonable performance and fuel economy for everyday driving. Its main drawbacks are its susceptibility to oil consumption and timing chain issues if not properly maintained. With diligent adherence to BMW's recommended maintenance schedule, particularly regarding oil quality and changes, the N46 can be a very reliable engine. It's not a performance powerhouse, but it's a solid workhorse.

What BMW models used the N46B20 engine?

The N46B20 engine was primarily used in various BMW 1 Series and 3 Series models, specifically the 18i and 20i designations. This includes models like the BMW E87 1 Series (118i, 120i) and the BMW E90/E91/E92/E93 3 Series (318i, 320i).

What is Valvetronic in the N46 engine?

Valvetronic is BMW's variable valve lift system. Unlike traditional engines that use a throttle body to control air intake, Valvetronic adjusts the intake valve lift to regulate the amount of air entering the cylinders. This precise control reduces pumping losses, improving both fuel efficiency and throttle response. In the N46, the Valvetronic control unit was integrated more closely with the ECU for enhanced performance.

How often should I change the oil in my N46B20 engine?

BMW typically recommends extended oil change intervals, often around 15,000 miles or every two years, whichever comes first. However, given the N46's known propensity for oil consumption and its sensitivity to oil quality, many experienced mechanics and owners recommend shorter intervals, typically every 8,000-10,000 miles or annually, especially if the car is driven hard or in stop-start traffic. Always use high-quality, BMW-approved synthetic oil.

What does the 'N' signify in an N46N engine?

The 'N' in the N46N designation indicates a modernised or updated version of the N46 engine. These revisions, introduced around 2007, included updates to the intake manifold, exhaust camshaft, and a switch to the Bosch MV17.4.6 control system, among other minor enhancements, leading to increased power output and improved efficiency.

Conclusion

While the BMW N42 and N46 engines share a common lineage, the N46 represents a refined evolution, incorporating numerous updates aimed at improving performance, smoothness, and electronic integration. Understanding these distinctions is crucial for anyone involved with these vehicles, from mechanics to owners. The N46B20, in particular, proved to be a versatile and widely used engine, offering a balanced package for its time. However, like any engine, it has its specific quirks, most notably concerning oil consumption and timing chain maintenance. By committing to regular servicing with the correct BMW-recommended parts and fluids, especially engine oil, owners can significantly extend the life and reliability of their N46 engine, ensuring many more miles of enjoyable driving.

If you want to read more articles similar to N42 vs N46: Unravelling BMW's 4-Cylinder Engines, you can visit the Engines category.