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

December 17, 2001
Edited by: James W. Burnes

Part IV: CONNECTING RODS, BEARINGS, and PISTON REPAIR

The connecting rods are babbitt-lined and shims are provided between rod and cap for bearing adjustment. Do not file cap to obtain correct bearing clearance. To adjust, remove enough shims (same amount from each side) so that rod is not quite free to move back and forth on shaft: add a .002 inch shim to each side and move rod back and forth again. If free, the clearance is correct. If necessary to add more shims to one side of rod, it is preferable that they be added to the camshaft side.

The rod side clearance (fore and aft movement on crankpin) should be .004 to .012 inch (Fig. A2) . If less than this, check for too tight a bearing fit, bent rod, or damagedside bearing surface on rod. The rod muft have correct side play and cause of incorrect clearance should be located. Align rods before installing as shown in Fig. A3.

PISTONS AND PINS

Pistons are cast iron, slipper skirt type with three rings located above the pin. Pistons are available from supply house in .003, .010, .020, .030 and .040 oversize. Measure piston for correct size on its skirt just below ring grooves and at right angle to the pin. Piston should have a clearance of .002 inch in its cylinder. Check the fit of piston in the cylinder as shown in Fig. A4. When checking with a 112 inch wide feeler, .002 inch thick, a light pull should be required to withdraw feeler. A feeler .003 inch thick should lock the piston in the bore.

Piston bosses are bushed to carry the pin. Three oversize pins are available for replacement when these bushings become worn; .003, .005, and .010 inch. Standard measurement of a new pin is .8645 - .8650 inch. Bushings must be reamed or honed to accommodate the oversize pins Correct fit of pin in bushings is a thumb push fit.

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