Cylinder Bore Scoring in Porsche 997 and 997.2 Models: Lokasil vs. Alusil Engine Blocks

Porsche, the iconic German car manufacturer, is synonymous with precision engineering and high-performance vehicles. Their 911 series, represented by the 997 and 997.2 models, is no exception. However, some owners of these particular models have reported an issue known as cylinder bore scoring. This concern, while not affecting all cars, has become a topic of much discussion among Porsche enthusiasts and experts alike.

What is Cylinder Bore Scoring?

Cylinder bore scoring refers to the appearance of vertical scratches or grooves in the cylinder walls. This can lead to a reduction in engine performance, increased oil consumption, and eventually engine failure if not addressed.

Causes and Symptoms

There are various reasons why bore scoring might occur, including:

• Inadequate lubrication
• Contamination in the oil
• Engine overheating
• Cold starts followed by high RPMs

The symptoms can range from an increase in oil consumption to noisy tappets, a rattling sound, especially when the engine is cold, or even visible smoke from the exhaust.

Lokasil vs. Alusil Blocks

Porsche uses a variety of materials for its engine blocks, but for the purpose of this article, we’ll focus on Lokasil and Alusil.

Lokasil: This is essentially an aluminum block with a silicon crystal lattice structure, however this hypereutectic alloy is localized in the cylinder bores only. The silicon particles provide added hardness to the cylinder surfaces, making them more resistant to wear. Porsche used a revised Lokasil III process starting with 997 Carrera models, where prior models used Lokasil I and II. There is no discernible difference in the failure rates with these different generations of Lokasil engine blocks.

Alusil: This is an aluminum-silicon alloy used for the construction of the entire 9A1/MA1 engine block used in the 997.2 model, rather than just having the high silicon aluminum localized in the cylinder bores with Lokasil blocks. Just like the Lokasil block, instead of using liners, the cylinder bores are etched to expose the silicon crystals which then provide a hard wearing surface. Pistons have an iron clad coating to prevent galling which would occur if there was aluminum to aluminum contact between the pistons and cylinders walls.

Bore Scoring in Lokasil and Alusil Blocks

The lack of a steel or cast iron liner in Lokasil and Alusil engine blocks increases thermal efficiency and cooling and reduces engine weight results in increased horsepower and torque. Both Lokasil and Alusil are designed to reduce friction between the piston rings and the cylinder walls. This reduction in friction translates to better engine efficiency and longevity. However, some Porsche 997 and 997.2 models have experienced bore scoring.

1. Lokasil Blocks: Bore scoring has been more commonly reported in these engines. Any debris or contaminants in the oil become trapped against the cylinder walls and are dragged by the piston rings, resulting in scratches. This occurs when there is a breakdown of the Al-Si cylinder system — most often this is caused when there are an insufficient amount of exposed silicon particles in the cylinder bores to support the required oil film or if the iron clad piston skirt coating fails. This results in aluminum to aluminum contact with scuffing and galling that generates the cylinder bore scoring found in 997 as well as prior 996 models.
2. Alusil Blocks: While the Alusil blocks in the 997.2 models tend to be more resilient than the Lokasil blocks, they are not immune to bore scoring.

Although cylinder bore scoring does occur, more common in these engines is piston seizing. Both result in damage to the pistons and cylinder bores with similar increased oil consumption, smoking, and piston noise.

Piston seizing occurs due to the very tight piston to cylinder clearances coupled with shrinkage of the cylinder bores in the area closest to the main bearing saddles.

Prevention and Treatment

The most common question that is asked is how to prevent cylinder bore scoring in Porsche 997.1 and 997.2 models.

• Regular Maintenance: Regular oil changes with high-quality synthetic oil with increased ZDDP and Moly levels such as Driven DT40 and DI40 can help reduce the risk.
• Warm-Up: Allow the engine to warm up properly before driving at high RPMs.
• Regular Checks: Listen for any unusual sounds from the engine, especially upon cold starts, and get regular inspections. Taking your Porsche to an expert in these models familar with the cylinder bore scoring issue is important to prevent cylinder bore scoring. Used oil analysis and bore scoping can be done to check to see if your engine has cylidner bore scoring.

If scoring is identified, a full engine rebuild will be necessary to correct for this issue.

In Conclusion

While cylinder bore scoring is a concern for some Porsche 997 and 997.2 owners, it’s worth noting that it doesn’t affect all cars. Regular maintenance, proper warm-up procedures, and being aware of any changes in your engine’s behavior are essential steps every owner can take to ensure their Porsche remains in top condition.