GM invested a great deal of development resources in the Vega, and introduced significant innovations. As is usually the case, some such innovations worked out while others did not.
Most folks forget or never knew that the Vega was designed for a two rotor Wankel engine. Unfortunately, the federales changed emissions regulations and GM decided that they could not make the Wankel meet such regulations while at the same time meeting reliability and fuel economy targets. Accordingly, they quickly designed a new 4 cylinder engine that could be economically manufactured by a hostile UAW work force, a handicap not evident in Germany or Japan.
The cast iron cylinder head had no expensive provisions for removing the camshaft other than from the front and did not have hydraulic cam followers. Shim adjustment of the cam followers, just about universal in OHC designs at the time, was impossible so the tapered screw type cam follower was developed. Easier to adjust lash than removing the camshaft to change shims, reliable, and cheap.
To control costs, the aluminum cylinder block was a high silicon, sleeveless die casting. Think about that a bit. The dies must be parted to remove the casting so the cylinder bores were Siamesed, the entire 4 cylinder siamesed bore part, not connected to the water jacket at the top of the block, a necessity to allow vertical parting of the dies. Innovative and easy to produce but head gasket failure became an issue until new head gasket materials were introduced for (IIRC) the 74 model year.
The cylinder bore part of the block vibrated vis a vis the water jacket at the head gasket, causing head gasket failure, and allowing coolant into the cylinders resulting in rapid failure of high silicon aluminum bores. The high silicon die cast aluminum block was not the issue. Head gasket failure was. This was eventually resolved but the damage had been done by that time.
Cost constraints were imperative so Engineering worked within such constraints in order to design a vehicle that could be sold at a profit, a necessity for any business to remain viable.
There is, of course much more to the Vega story, and this brief synopsis is highly condensed for purposes of time.
Of course, in hind sight, some decisions should have been made differently. Such it true of just about any innovative endeavor.
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