SIX CYLINDERS are used in the Chevrolet engine, because six cylinders give smoother action and a longer range of satisfactory performance than four. Maximum results per dollar has been the ideal in the design, and high output has been secured at a cost very little higher than for a four-cylinder engine.
The piston displacement is large enough to give satisfactory performance without fine tuning. The bore is made as large as possible within the space required for water-cooling around the valves. The stroke is short, resulting in low inertia forces and a stiff crankshaft with the minimum amount of metal. Three main bearings are found sufficient, because of the stiffness of the shaft and the inherent balance of the groups of three cylinders.
Positive lubrication is provided, without pressure. The overhead-valve mechanism is so proportioned and the cooling of the parts is so arranged that variations in expansion cancel each other and result in nearly constant valve clearance. The combustion-chamber represents an advanced application of the thermodynamic principles of combustion control.
Differences of opinion are freely expressed in the discussion. The splash lubrication is questioned by several, but is defended by Chairman Round. Mr. Taub explains that the use of pressure lubrication is almost impossible, in big volume production, without an automatic method for cleaning the drilled oil-holes, and says that stroboscopic study shows two injections of oil per revolution into the connecting-rod bearings.
Other features that come in for questioning are the three-bearing crankshaft, the three-port inlet-manifold and the possibility of steam-cooling. Mr. Taub shows that the crankshaft adopted gives the maximum in value per dollar, and reports creditable wear tests. The basis of automobile taxation in Europe is said to dictate the small bore and to be an effective defence against the importation of American cars. Mr. Taub illustrates the better distribution secured by a three-port than by a four-port inlet-manifold.