How to Identify a Chevy Small Block Flywheel

by Floyd Drake III
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Flywheels are mounted to the rear of the engine on manual shift vehicles -- just before the clutch assembly and transmission -- and are covered by the bellhousing. The primary purpose of the flywheel is to provide momentum for the running engine; it must be properly balanced. The secondary purpose is to mate with the starter motor; this allow the starter motor to crank the engine. Installing the wrong flywheel can cause severe engine damage.

Step 1

Measure the diameter of the flywheel with a machinist's ruler. According to Jam Performance Transmissions, the flywheel sizes for small-block Chevrolet engines are the 12.75 inch and the 14 inch. The14-inch flywheel is used on the 400 cubic-inch small-block and big-block Chevrolet engines.

Step 2

Count the gear teeth on the perimeter of the flywheel. The 12.75-inch flywheel has 153 teeth; the 14-inch flywheel has 168 teeth. The only small-block Chevrolet engine that uses the 14-inch, 168-tooth flywheel is the 400 cubic-inch.

Step 3

Look for a counterweight. All Chevrolet small-blocks are internally balanced, with the exception of the 400 cubic-inch small-block, the 400 cubic-inch engine-flywheel has a counterweight mounted to the flywheel plate.

Step 4

Determine the flywheel-flange bolt pattern. These are the bolt holes found around the center of the flywheel. According to GM Parts Direct, 1955 to 1985 small-block Chevrolet flywheels have a 3.58-inch bolt pattern, whereas 1986 and later flywheels have a 3-inch bolt pattern. Determine the bolt pattern by measuring the distance between the bolt holes. Some 350 cubic-inch and smaller engine-flywheels have bolt holes to accommodate both patterns

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