Chevrolet Corvair: Encyclopedia II - Chevrolet Corvair - Engineering

Chevrolet Corvair - Engineering

The Chevrolet Corvair engine, unique for an American car, presented a different set of requirements for mechanics, many of whom treated the engine in the same way as they would an engine of normal design, leading to problems.

An engineering weakness not generally highlighted related to fumes and gases entering the passenger area via the heater system, a problem endemic to an air-cooled engine that uses heat radiated from the engine directly to heat air for the passenger compartment. Carbon monoxide and other noxious or deadly gases could enter the sedan passenger areas if exhaust system gaskets aged or failed using this system, since the gaskets were inside the heater box air intakes and air for engine cooling and passenger heating was mixed together as one common airflow. The 1960 model Corvairs used a GM Harrison division gasoline heater located in the front trunk area, as its standard heater, similar to the Eberspächer heater offered as an auxiliary heater by Volkswagen as a dealer-installed option. It operated independently from fuel in the cars' gas tank, but this feature became optional in 1961 and was dropped in 1965 due to weak consumer demand. Chronic oil leakage from the pushrod tubes, caused by GM's poor choice of pushrod tube seal material, also contaminated the passenger heating air. That air might also become noxious if a 6-inch (152 mm) wide rubber seal almost 16 feet (5 m) long, located between the engine assembly and the body, was not maintained in like-new condition. Another common problem in the earlier years was oil leakage caused by dissimilar metal thermal expansion on the aluminum and steel engine. Chevrolet wrestled with several problems of this nature the entire time the Corvair was in production with varying degrees of success.

The interior air would also be contaminated if the voltage regulator allowed an over-voltage condition and the original battery vent hoses were not attached. The battery, which was mounted in the engine compartment, could emit sulfuric acid vapor if overcharged. Chevrolet installed special battery caps and hoses that vented the battery to air outside the engine compartment, but these were often discarded by owners during the car's life. The Volkswagen Beetle (Type I), another automobile with an air cooled engine, located the battery in the passenger compartment under the rear seat. This may have been a source of noxious interior fumes in that vehicle as well, and was also a fire hazard if the battery terminal insulator was not placed over the battery and someone or something heavy sat on the seat. The Beetle heater system better isolated fresh air from engine cooling air fumes, and was only susceptible to carbon monoxide contamination from the two heat exchanger to muffler seals at the rear of the engine, as opposed to the eight exhaust joints in the Corvair system. The VW Beetle, likewise, was susceptible to poor engine perimeter seal maintenance resulting in contaminated air being sucked into the cooling fan, which supplied passenger compartment heat as in the Corvair.

This air contamination problem is illustrated by the fact that many American cities' taxi regulations had prohibited air-cooled engine cars from being used as taxicabs when they derived their heated air from engine exhaust heat, decades before the Corvair and VW Beetle entered the market.

A criticism in Lawyer Ralph Nader's 1965 book concerned the steering column design. Like most cars of its era, the Corvair's steering column was rigid and could impale the driver in a front-end collision. While the Corvair's steering box was mounted ahead of the front cross-member, it was well behind the frame horns, in what would later be called a "crumple zone," and could, in a severe front-end collision, push the steering column and steering wheel toward the driver. In practice, most driver chest injuries were sustained due to the lack of a shoulder belt, rather than steering column intrusion. Any increase in risk of injury due to steering column intrusion in a front-end collision was, however, more than offset by the absence of an incompressible engine and transmission in the front of the vehicle, which commonly intruded into passenger compartments on vehicles of the era. Chevrolet, aware of Nader's criticism, changed the steering shaft to a two-part design with a frangible joint in the 1966 model year, and a collapsible steering column was provided in 1967, towards the end of the model's life span.

In defense of Nader's criticism of the Corvair's swing axle rear suspension, some writers have pointed to a critical factor in the combination of soft "American-style" springs together with an unusually large and heavy engine for a rear-engine, air-cooled car. Both of these factors would have greatly increased the potential for excessive body lean and over-cambering of the suspension in sharp turns, as compared with smaller and lighter contemporary Volkswagens, Renaults, Porsches, and other rear-engined cars. In addition, the car was designed to avoid terminal oversteer by using very low air pressure in the front tires, typically 12 to 15 pounds force per square inch (80 to 100 kPa), so that they would begin to understeer (slip) before the swing axle oversteer would come into play. Although this pressure was quite adequate for the very lightweight Corvair front end, owners and mechanics, either through ignorance of the necessity for this pressure differential between front and rear or thinking that the pressure was too low for the front, would frequently inflate the front tires to more "normal" pressures, thus ensuring that the rear of the car would lose traction before the front, causing it to oversteer. It should be mentioned that the Corvair is by no means unique in requiring dissimilar front and rear tire pressures for normal controllability. The Ford Explorer had widely-publicized stability problems when equal pressures were used. See Firestone vs Ford Motor Company controversy.

Although Nader probably overstated the severity of the handling problems, as was later found by US National Highway Traffic Safety Administration investigators, Chevrolet made changes to the suspension: in 1964, adding a transverse leaf spring extending between the rear wheels to limit rear wheel camber change. In 1965 the Corvair got a state of the art fully independent rear suspension closely resembling that of the contemporary Corvette, even sharing some components. These changes were, however, viewed as Chevrolet's recognition of possible problems with the original design.

Adapted from the Wikipedia article "Engineering", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki