Chevrolet Corvair engine: Encyclopedia II - Chevrolet Corvair engine - Problems

Chevrolet Corvair engine - Problems

The Corvair engine design was so unique that good dealer service and maintenance was spotty. Mechanics, unused to the aluminum head and crankcase, would frequently overtighten threaded fasteners and spark plugs, stripping the threads out of the aluminum, requiring extensive repair.

Due to the greater thermal expansion of aluminum, valve clearances had to be measured at operating temperature. When they were measured on a cold engine, engines frequently and incorrectly were diagnosed as needing "valve jobs" early in their life. In fact, the valve train in most engines usually functioned perfectly for well over 100,000 miles.

Early engines were subject to frequent failures of the head gasket, between the heads and the cylinder barrels; this was addressed in later models by increasing the width of the sealing area.

The large cooling fan located on top of the engine required the fan belt to bend from the vertical plane of the crankshaft to the horizontal plane of the fan, causing additional stress. Chevrolet engineers designed a unique fan belt, which many owners and dealers replaced with an inappropriate design. The correct fan belt, properly installed to proper tension, worked well, while other belts even of proper size installed loose or tight would break frequently, giving the engine fan and belt design an undeserved bad reputation. Since failure of the cooling fan on an air-cooled engine leads to immediate overheating much more quickly than in a water-cooled engine (within 15 seconds at the high rpms when the belts were likely to fail), mechanically inclined owners would routinely carry a spare belt and the 9/16 inch box wrench needed to change the belt, in addition to adding a large and eye catching warning light in parallel with the normally sized factory generator/alternator warning light. Aftermarket manufacturers made available differently sized pulleys which reduced the fan speed to 1.3 or 1.2 times engine speed, rather than the stock 1.5; this reduced the tendency to throw or break a fan belt for engines which spent most of their time at higher rpms.

The pushrods were located below the cylinders, each in a separate metal tube between the crankcase and the head; these tubes also served to return oil from the head to the crankcase, and were fitted with neoprene O-rings at each end. After a short time, the neoprene exposed to the intense heat of the head lost resilience and developed a tendency to leak oil which became characteristic of Corvairs; unfortunately, since engine cooling air was diverted to the interior heater, this caused an unpleasant odor. Improved elastomer O-rings with much greater durability became available from aftermarket suppliers.

In the original stock four carburetor engine, only the two primary carburetors were equipped with idle circuits, for simplicity in tuning. However, with the progressive nature of the linkage, if the engine did not spend much time near full throttle there would be no fuel flowing through the secondary carburetors; as a result, the stagnant gasoline in their float bowls would continuously evaporate and leave a residue which built up, eventually completely destroying the carburetor. In the later versions of the engine, idle circuits were included in all four carburetors to prevent this problem, and there was a great deal of retrofitting and replacement of the older secondaries by owners. However, this in turn required that all four idle adjustments be balanced for a tuneup, which could be a problem in itself.

The progressive throttle linkage of the four barrel model was constructed simply and cheaply with rods simply passing through holes in bell cranks, rather than Heim joints; as a result it rapidly became imprecise and grew even worse with wear, making tuning the engine an exercise in futility. Some owners laboriously modified the linkage with precision components, but more purchased an aftermarket kit to rotate the carburetors through ninety degrees and attach the now colinear throttle shafts of the two carburetors on each side together, thereby greatly simplifying the linkage, as well as eliminating the problem of the secondaries becoming clogged from lack of use, mentioned above. However, this also eliminated the progressive feature of the stock carburetor linkage, so that performance could not be optimized both at low to midrange rpm and at high rpm.

Other owners replaced the four single-barrel carburetors with a single four-barrel carburetor, centrally mounted on a manifold with four long arms that attached to the original carburetor mounting pads on the heads. While this caused the carburetor and manifold to be slow to warm up to operating temperature and therefore caused problems with flooding and cold temperature operation, it eliminated linkage problems, simplified tuning the carburetor, and provided access to the large variety of four-barrel carburetors available on the market.

A factor which would have, in itself, led to the demise of the air cooled engine design was the rapid and relatively large temperature variation of the air-cooled engine with variations in load and rpm; this would have made meeting the upcoming emissions requirements of the 1970s difficult. The head temperature gauge with which the Corsa was equipped would visibly swing up and down as the car traveled between sunlit and shaded portions of the highway.

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