The Chevy Vega was conceived in 1968 as a simple, low-cost vehicle to utilize the newly-developed all-aluminum die-cast engine block technology. The first sand cast aluminum blocks were actually produced a full two years prior to the corporate decision to build the Vega. The technical breakthroughs of the block lay in the die-casting method used to produce it, and in the silicon alloying which provided a compatible bore surface without liners. With a machined weight of 36 pounds, the block weighed 51 pounds less than the 4-cylinder cast-iron block in the Chevy II. A relatively large displacement engine with good low speed torque was chosen. Economy would be achieved through the use of low numerical gear ratios, which would keep engine rpm low. The Vega engine itself went through 6,000,000 driving miles of testing. The earliest version of the engine was tested in a Fiat 124 sedan. This car was used for development of the aluminum block.The engine was a joint effort from General Motors, Reynolds Metals, and Sealed Power Corp. Reynolds developed an 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. Sealed Power developed special chrome-plated piston rings for the engine that were blunted to prevent scuffing. The engine and its die-cast block technology was developed at GM engineering staff long before the program was handed-off to Chevrolet to finalize and bring to production.
Ed Cole, who had been very personally involved with the design of the 1955 Chevrolet V8 as chief engineer at Chevrolet, was equally involved with the Vega engine as GM president, and was a frequent visitor on Saturdays to the engineering staff engine drafting room, reviewing the design and giving direction for changes. Chevrolet engineers and manufacturing personnel weren't pleased, especially since they knew Ed Cole wanted the job done quickly. As the engine development progressed at Chevrolet, it became known (in closed offices) as "The world's tallest, smallest engine" due to the tall cylinder head. Plagued by vibrations, noisy operation and prone to overheating, the engine did not live up to the Vega's potential. By 1974, the overheating and vibrations were a thing of the past and the noise had been reduced to an acceptable level.
The Vega engine is a 140 CID (139.6 cu in) 2,287 cc inline-4 featuring a die-cast aluminum cylinder block and a cast-iron cylinder head with a single overhead camshaft (SOHC). The cylinder block is an open deck design with siamesed free-standing linerless cylinder bores. Outer case walls form the water jacket and are sealed off by the head and the head gasket. The block has cast iron main caps and a cast iron crankshaft. The cast iron cylinder head was chosen for low cost and structural integrity. The overhead valvetrain is a direct acting design of extreme simplicity. Only three components activate the valve rather than the usual seven of a typical push rod system. The camshaft is supported by five conventional pressed-in bearings and is driven from the crankshaft by an externally mounted continuous cogged belt and sprocket
system. Six v-grooves on the outside of the belt drive the water pump and fan. The large bore and long stroke design provide good torque and lower rpm operation for reduced wear. Compression ratio for the standard and optional engine is 8.0:1, as the engine was designed to operate on low-lead and no-lead fuels. A single-barrel carburetor version produces 90 hp. The two-barrel version (RPO L11) produces 110 hp. From 1972 on, ratings were listed as SAE net.
The relatively large (for an inline-4) engine is naturally prone to vibration and is subdued by large rubber engine mounts. The 1972 Rochester DualJet two-barrel carburetor required an air pump for emission certification and was replaced in 1973 with a Holley-built 5210C staged two-barrel carb. Emission control revisions made in 1973 reduced power output on the optional engine by 5 bhp, although the engine's cruising noise levels were reduced. H.E.I. ignition was introduced on 1975 engines. Non-air conditioned cars have a small 12-inch by 12-inch radiator core. The reason for the relatively small radiator was the aluminum engine block and its superior heat conductivity as compared to iron.
The linerless aluminum block has been blamed for a large share of the Vega's poor reputation. An iron engine could survive moderate overheating, but the Vega could not. The major problems with the engine (head gasket material etc) were sorted out the car's first year, with refinements made annually. Chevrolet added a coolant overflow bottle and an electronic low-coolant indicator in 1974 that could be retrofitted to earlier models at no cost. In May 1974 under a revised 50,000 mi engine warranty for 1971–1975 Vegas. Chevrolet informed the 1.3 million owners that it would repair, at its own expense, any engines damaged by overheating. In 1976, the engine now named Dura-built 140, had hydraulic valve lifters, cooling refinements including new cooling slots to the block; revised water pump and thermostat, new longer-life valve seals cut oil consumption 50%. But the revamped engine with its 5 year/50,000 mile engine warranty failed to boost the public's confidence in the car.
In hindsight there were safer engine options. Before the car was introduced, Chevrolet did their version of the Vega engine substituting a sohc Hemi aluminum cylinder head in place of the sohc cast-iron head. It was rejected by GM top brass (probably because of higher cost) It has been said this stillborn version developed more power and wouldn't have had the thermal expansion problem of the production engine. The cast iron 151 cid OHV 4-cyl. engine used in the 1970 Nova could have been easily used, and later was, revamped as Pontiac's "Iron Duke 2.5 Liter" for the final model year Pontiac Astre (Vega clone) in 1977 then continued in the Vega's wake, the std. engine in Vega-derived variants Chevy Monza and Pontiac Sunbird in 1978-1980.
Aluminum engine troubles have not been confined to the Vega. . It's taken decades to make auto aluminum engines as reliable as their heavier cast-iron counterparts. One factor remains - overheating an aluminum engine must be avoided.
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