Cylinder Bore Scoring - Part 1: What is it about? - with Lake Speed Jr.

What is cylinder bore scoring and how does it affect my Porsche vehicle? Models with Lokasil or Alusil hypereutectic engine blocks can suffer from cylinder bore scoring caused by a breakdown of the Aluminum/Silicon piston/cylinder/ring system.

The most well known example of this was the Chevrolet Vega’s hypereutectic engine block cast out of Reynolds A390 (now known as Kolbenschmidt’s Alusil).

Lokasil was used in Porsche Boxster, Cayman, and 911 models from 1997-2008; Alusil cylinders have been used in many Aircooled and watercooled Porsche engines including the 2.7 and 3.0 SC, 944, 968, 928 and most recently, Cayenne, Panamera, Macan, and sports car models with the 9A1/MA1 engine.

So what makes a hypereutectic cylinder different than one that is Nikasil plated? Where a cylinder or block might been Nikasil plated that provides a hard coating comprised of nickel, silicon, and carbide, Alusil and Lokasil cylinders have raw aluminum bores that require special preparation to expose the silicon particles present in the aluminum. The pistons are then iron coated to provide a barrier between the aluminum bore and aluminum piston skirt.

The oil film on the cylinder bore surrounds these silicon particles and forms the tribofilm that supports the piston and ring system. Formation of this tribofilm is critical to proper operation of engines with Alusil and Lokasil cylinder bores (and why choice of oil is so important).

If there is a breakdown of the iron coating on the piston or too many of the silicon particles fracture, the cylinder system fails and bore scoring is the end result.

One of the tools that are invaluable to evaluating cylinder bores is a profilometer to determine the bearing area curve. Not understanding the importance of proper surface finishes and measuring them can lead to problems when rebuilding any engine.

Watch Lake Speed Jr. and Charles Navarro in this installment on bore scoring evaluate surface finishes using the Mitutoyo Surftest SJ-201 profilometer in evaluating cylinder bore scoring failures.