LS Block Sleeving at Oztrack
LS blocks, particularly LS3 and LSA, have a significant problem with core shift from new. This gives them weak, thin spots in the cylinder walls that can crack easily, and big power stock engines boosted, etc., are vulnerable; we have seen recently many blocks with cracked sleeves in the past 12 months. This can be fixed with aftermarket sleeving.
We can now, with our new CNC machine install them at Oztrack. It involves boring a counterbore, using dry ice or liquid nitrogen to install the sleeves, and then CNC boring and torque plate honing to suit the desired pistons.
How does core shift occur?
The casting method is typically used during the manufacturing process of an engine block, including LS3 blocks. Here’s an overview of how core shift can occur during manufacturing:
- Mould preparation: A mould is created based on the design specifications of the engine block. The mould consists of multiple sections that form cavities representing the shape and dimensions of the block.
- Core placement: Cores are inserted into the mould to create the voids where the cylinders will be formed. Cores are typically made of sand or other materials that can be easily removed once the casting is complete.
- Molten metal pouring: The molten metal, usually aluminium or cast iron, is poured into the mould to fill the cavities and surround the cores. The metal will solidify and take the shape of the mould.
- Cooling and solidification: As the molten metal cools, it solidifies, forming the engine block. During this cooling process, the metal undergoes contraction and shrinks slightly.
Core shift can occur during the casting process due to a few reasons:
- Core misalignment: There can be misalignment issues if the cores are not precisely positioned within the mould. This misalignment can cause the cores to shift slightly during the pouring and solidification of the molten metal.
- Uneven cooling: As the molten metal cools and solidifies, it undergoes thermal contraction. If the cooling is uneven across the block or there are temperature gradients within the casting, it can lead to uneven shrinkage and potentially cause the cores to shift.
- Mould movement: During the pouring of the molten metal, the force and weight of the metal can cause the mould to shift or vibrate slightly. This movement can result in the displacement of the cores within the mould.
These factors can contribute to core shift, where the cylinder walls are not in their intended positions within the engine block. The core shift can lead to uneven cylinder wall thicknesses, compromised sealing, and potential issues with piston fitment, resulting in reduced engine performance and reliability.
Sleeving
How does the sleeve stay in the cylinder?
Cylinder sleeves are typically installed into the cylinder using an “interference fit” (sometimes referred to as “press fit”). This means the size of the block or cylinder bore is smaller than the outside diameter of the sleeve. The sleeve is “pressed” into the cylinder and the size variance holds the sleeve in place. Generally, the interference fit for the sleeve to a cast iron bore is .0025″. And for an aluminium bore, the interference fit is .004″.
The sleeves usually have a lip at the top that has a larger diameter than further down, and when the CNC machine bores the cylinders, it needs to bore the larger size for the lip. This is called a counterbore.
Sleeves are made of a better grade of cast iron than the original sleeves , cast iron alloy of carbon-chrome and molybdenum or or ductile iron.
We install sleeves at Oztrack in Penrith, Sydney.
We can save LS blocks at the cylinder’s boring tolerance limits or with cracked sleeves. From collected dyno data, we also find that sleeved engines make more power and torque.
