LS ENGINE BLOCK SLEEVING
LS blocks in particular LS3 and LSA have a significant problem with core shift. This gives them weak 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 and using dry ice or liquid nitrogen to install the sleeves, then CNC boring and torque plate honing to suit the desired pistons.
How does core shift occur?
During the manufacturing process of an engine block, including LS3 blocks, the casting method is typically used. Here’s an overview of how core shift can occur during manufacturing:
- Mold preparation: A mold is created based on the design specifications of the engine block. The mold consists of multiple sections that form cavities representing the shape and dimensions of the block.
- Core placement: Cores are inserted into the mold 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 aluminum or cast iron, is poured into the mold to fill the cavities and surround the cores. The metal will solidify and take the shape of the mold.
- 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: If the cores are not precisely positioned within the mold, there can be misalignment issues. 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 if there are temperature gradients within the casting, it can lead to uneven shrinkage and potentially cause the cores to shift.
- Mold movement: During the pouring of the molten metal, the force and weight of the metal can cause the mold to shift or vibrate slightly. This movement can result in the displacement of the cores within the mold.
These factors can contribute to core shift, where the cylinder walls are not in their intended positions within the engine block. Core shift can lead to uneven cylinder wall thicknesses, compromised sealing, and potential issues with piston fitment, resulting in reduced engine performance and reliability.
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 aluminum bore the interference fit is .004″.
The sleeves usually have a lip at the top that has a larger diamater than further down and when the CNC machine bores the clinders 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 molybdenumor or ductile iron.
We install sleeves at Oztrack in Penrith, Sydney