Reconditioning High Silicon Aluminum Alloy Engine Blocks

One of the most significant features of aluminum die-cast engine blocks is that they don't require steel or cast iron liners in the cylinder bores. Particles of pure silicon, averaging about .001" in diameter are dispersed throughout the engine block. As silicon is very hard, there will be very little wear in the cylinder bores. In fact, as far as pistons and rings are concerned, the cylinder wall IS silicon; the aluminum's function is simply to hold the silicon particles.

Reconditioning Hints

If cylinder bores in these blocks become excessively worn or scored, they can be honed to accept oversize pistons. Unfortunately, the sizing and finishing processes you would normally use leave cylinder wall of silicon and aluminum. The silicon particles no longer protrude from the aluminum.

To achieve the proper surface for compatibility with the rings and pistons you will need to prepare the cylinder bores so the silicon particles protrude. This allows the pistons and rings to only contact silicon. A special conditioning operation is required to remove the aluminum from between the silicon particles.

Let's start with the tools and supplies

In addition to the items listed below you will need an electric drill (1/2" or 5/8") that will run at 350RPM. You may also need a dial bore gauge and a quick coupler such as the Sunnen AN-80.

Reconditioning Procedures

Before you start honing, place a soft steel or aluminum washer in the bottom of each cylinder. This will prevent you from hitting the main bearing webs and damaging stones.

We also recommend using a continuous flow of honing oil for steps 1, 2 and 3. 

Diagram showing where to remove abrasive from honing stones

One last thing to do in preparation for honing. You will need to remove 1" from the top of the stones as illustrated. Cut through the abrasive using an old hacksaw blade then break off the unwanted piece of stone. DO NOT cut into the stone holder.

  1. Roughing Operation
    Hone to within 0.08 nun (.003 in) of finish diameter using the MM33-J63 stones. Remember to use a continuous flow of honing oil.
  2. Finishing Operation
    Hone to within .001" (0.03mm) if finish diameter using the MM33-J85 stones.
    Stock Removal Rate: 0.002 in/min (0.05mm/min).
    Stone Wear/Stock Removal Ratio: 2/1.
    Surface Finish: 15-20 Ra µ in (0.4-0.5 Ra µ m.
  3. Polishing Operation
    Wipe the cylinder clean and hone to the finish diameter using the MM33-CO5 Cork stones. Tighten the feed pinion as needed.
    Stock Removal Rate: .0007 in/min (0.02 mm/min).
    Stone Wear/Stock Removal Ratio: 2/1
    Surface Finish: 4-6 Ra µ in (0.1-0.2 Ra µ m.
  4. Conditioning Operation
    DO NOT 
    use a continuous flow of Honing Oil during this operation.
    Saturate the MM33-FO5 Felt set with honing oil.
    Wipe the cylinder clean.
    Thoroughly mix Silicon compound (AN-30), then apply a heavy coat to the felt set and the entire polished surface of the cylinder wall.
    IMPORTANT: Avoid contamination of the silicon compound by keeping the container closed between applications. Always use a clean brush when applying the compound and DO NOT REUSE the compound.
    Tighten the Feed Pinion as tightly as possible using your fingers. DO NOT over-tighten or use pliers.
    Turn power on and hone the cylinder for 1-1/2 minutes or 85 strokes using a steady, even stroking motion; over-stroke the end of the cylinder by 1/8" (3mm). Periodically tighten the Feed Pinion to compensate for felt set wear.
    As the felt set wears, replace to avoid scoring the cylinder with the stone holder.

The finished cylinder surface will have a dull matte finish. Repeat for each cylinder. Finally, carefully wipe cylinders clean.

To avoid contamination, store felt sets separately in a clean storage box.

WARNING: The used oil-saturated felt sets contain mineral oil which is classified as a hazardous waste. Dispose of according to applicable government regulations. 

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