GM 2300 Engine - Aluminum Engine Block

Aluminum Engine Block

GM Research Labs had been working on a sleeveless aluminum block since the late '50s. The incentive was cost. Engineering out the four-cylinder's block liners would save $8 per unit — a substantial amount of money at the time. Reynolds Metal Co. developed an eutectic aluminum alloy called A-390, composed of 77 percent aluminum, 17 percent silicon, 4 percent copper, 1 percent iron, and traces of phosphorus, zinc, manganese, and titanium. The A-390 alloy was suitable for faster production diecasting which made the Vega block less expensive to manufacture than other aluminum engines. Sealed Power Corp. developed special chrome-plated piston rings for the engine that were blunted to prevent scuffing.which was suitable for faster production diecasting, making the Vega block less expensive to manufacture than other aluminum engines. Sealed Power Corp. developed special chrome-plated piston rings for the engine that were blunted to prevent scuffing. Basic work had been done under Eudell Jackobson of GM engineering, not at Chevrolet. But then, suddenly, Chevrolet got handed the job of putting this ohc sleeveless, aluminum block into production — a feat never before attempted.

The Vega engine block was cast in Massena, New York, at the same factory that had produced the Corvair engine. Molten aluminum was transported from Reynolds and Alcoa reduction plants to the foundry, inside thermos tank trucks. The block was cast using the Accurad process. The casting process provided a uniform distribution of fine primary silicon particles approximately 0.001 inches (25 µm) in size. Pure silicon provides a hard scuff and wear resistant surface, having a rating of 7 on the mohs scale of hardness, the same as quartz, as compared to diamond which is 10. The blocks were aged 8 hours at 450 °F (232 °C) to achieve dimensional stability. The technical breakthroughs of the block lay in the precision die-casting method used to produce it, and in the silicon alloying which provided a compatible bore surface without liners. Before being shipped to Tonawanda, the blocks were inpregnated with sodium silicate, where they were machined through the outer skin. From Massena, the cast engine blocks were shipped as raw castings to Chevy's engine plant in Tonawanda, New York. Here they underwent the messy etch and machining operations. The cylinder bores were rough and finish-honed conventionally to a 7-microinch (180 nm) finish then etched by a new (then) electro-chemical process. The etching removed approximately 0.00015-inch (3.8 µm) of aluminum leaving the pure silicon particles prominent to form the bore surface.

With a finished weight of 36 pounds (16 kg), the block weighs 51 pounds (23 kg) less than the cast-iron block in the Chevy II 153 cu in (2,510 cc) inline-4. Plating the piston skirts was necessary to put a hard iron skirt surface opposite the silicon of the block to prevent scuffing. The plating was a four layer electo-plating process. The first plate was a flash of zinc followed by a very thin flash of copper. The third and primary coating was hard iron, 0.0007 in (18 µm) thick. The final layer was a flash of tin. The zinc and copper were necessary to adhere the iron while the tin prevented corrosion before assembly of the piston into the engine. Piston plating was done on a 46 operation automatic line. From Tonawanda, the engines went to the Chevrolet assembly plant in Lordstown, Ohio.

Eudell Jackobson of GM engineering pointed out one of the early problems with unexplained scuffing and discovered excessive pressure on the bore hones was causing the silicon to crack. This need to both develop and actually manufacture the engine was a product of the program schedule. He said, "...We were trying to put a product into production and learning the technology simultaneously. And the pressure becomes very, very great when that happens. The hone-pressure problem was solved before engines actually went out the door, affecting pre-production engines only."