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Chevy 265-cid V-8 Engine


Chevy 265-cid V-8 Engine Overview

One of the outstanding features that made the 265 such a watershed development was the lack of a common rocker shaft. Each rocker arm was entirely independent of the others, so that deflection of one had no effect on the others. Each was assembled over a valve stem and pushrod, retained by a fulcrum ball, and lock nut. Regardless of whether mechanical or hydraulic valve lifters were used, the valves were lashed by turning the lock nut. In addition, this arrangement reduced reciprocating weight, which allowed higher rpm and cut down on raw materials. The intake manifold provided a common water outlet to both heads. The heads were die-cast with integral valve guides, and were completely interchangeable. The valvetrain design was shared with the year's slightly larger Pontiac V-8, which was designed along the same lines.

A short stroke meant connecting rods - just 5.7 inches center distance for a stroke ratio of 1.9. Pressed-in piston pins eliminated the slitting of the rod and the need for a locking bolt. Five main bearings of equal diameter carried maximum loads in their lower halves. "By reducing the maximum oil film loads, through omission of the oil groove in the lower half", noted the SAE Journal, "the capacity of the main bearings is increased approximately 100 percent, and wear is reduced."More weight was saved by circulating the oil through hollow pushrods, providing splash lube to the rockers and valve stems. This meant that separate and costly oil feeder lines were unnecessary.

Further details included "autothermic" pistons with three rings, slipper-type aluminum units with a circumferential expander for the single oil ring providing axial and radial force to control oil burning. Instead of alloy iron, the crankshaft was made of pressed forged steel because of its higher specific gravity and modulus of elasticity. Newly developed forging processes allowed Chevrolet to reduce overall crank length. A chart of torsional vibration showed very low peaks without sharp points throughout most of the range; adding a harmonic balancer eliminated remaining torsional vibration.

The exhaust manifolds were routed near the top of the cylinder heads, with exhaust passages pointing upward and out, and the entire length of the ports was water-jacketed. "This minimizes the transfer of distortion loads back to the valve seats," the Journal noted, "and dissipates heat uniformly from the valve area. Chevy switched to a 12-volt electrical for the 265 that provided more efficient generator output, better starter-motor operation, and adequate voltage for the powerplant's higher compression.

Because the new engine had better heat rejection properties than the "Blue Flame Six," a smaller radiator could be used, which reduced rate and frontal radiator area. Overall, the V-8 was actually 41 pounds lighter than the six. This was in keeping with the concept of the '55 Chevy which was, as Ed Cole said, "built around lighter components."


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