Engine Reconditioning Overview & Tips
For your 1929-1955 Chevrolet Straight Six Engine

November 26, 2001
Edited by: James W. Burnes

Part I: INTRODUCTION OF THE STRAIGHT SIX

The last four-cylinder Chevrolet engine was manufactured in 1928 and the following year a six cylinder made its public appearance. These engines had forged alloy steel crankshafts supported in three main bearings. The camshaft also ran in three bearings. Pistons were cast iron.

The 1932 engines had a counter-balanced crankshaft. With a compression ratio of 5.2:1, 60 hp was developed at 3000 rpm. A new type down-draft carburetor was equipped with an air cleaner. Main bearings and camshaft bearings were pressure lubricated by a vane-type pump. A low pressure line lubricated the valve rocker shaft and replenished the connecting rod dipper troughs.

A new cylinderhead design and valve arrangement was introduced in the 1934 Chevrolet. The valves were now staggered in the cylinderhead and with a 5.45:1 compression ratio 80 hp was developed at 3300 rpm. (previously 65 hp at 2800 rpm).

In the 1935 engines high pressure jet oil streams were used to lubricate the connecting rod bearings. Pistons were tin-plated to a thickness of .001 in.

In 1937 important engine changes were introduced; the new engines had a bore and stroke of 3 1/2 x 3 3/4 in. instead of 3 5/16 x 4 in. as formerly used. The compression ratio was raised from 6:1 to 6.5:1. The most important improvement was the introduction of a four bearing crankshaft and main bearing area was stepped up 8% thereby. Replaceable bearing shells were adopted and,the caps were fitted with shims. Also new were the dome-head slipper-type pistons. Connecting rods were shorter and stiffer and a gear-type oil pump replaced the vane-type previously used. The rated output was 85 hp at 3200 rpm.

Apart from minor modifications subsequent engine models remained basically the same. In 1941, the cylinder head was redesigned and flat pistons were used. With a compression ratio of 6.5:1, the engine developed 90 hp at 3300 rpm.

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