Repair 7

Confirm that the Vehicle is a Chevrolet. With the exception of the 1984 through 1987 pickup truck model years, Chevrolet for more than three decades has only used the Chevy V6. So if it is a Chevrolet built since 1977, chances are good it has the Chevy V6 engine.

Identify the engine as a 6-cylinder. The best way to differentiate a 6-cylinder engine from other engines is to count six spark plugs, three on each side.

Locate the ID number on the engine block. According to Nasty Z28, the numbers are located on the passenger side of the block behind the distributor. On a front wheel-drive, look behind the distributor.

Decode the engine ID number. The Chevrolet engine ID number is usually seven to eight digits long. It features numbers and letters, with a prefix and a suffix. The suffix is three letters long and identifies the engine size, horsepower and vehicle model. In engine number V0106CMJ, for example, "CMJ" is the suffix. The preceding prefix numbers supply information about the date and location of the vehicles production.

Contact a Chevrolet parts department with the full engine ID number. They can decode it for you. Or you could visit GM Parts Direct online. Either type the number in the search box or send a message to the customer service department and they will decode it for you.

Identify the casting lug-nut on the engine block. It is located on the right side as you face the front of the engine, towards the bottom. There will be a lug nut attached to a stud. According to HotSixes, differentiate the size V6 using the following data: the 200 c.i.d. has no lug nut; the 229 c.i.d. has one lug nut; and the 262 c.i.d. has two lug nuts, one on the right and left sides of the block.

Measure the diameter of the flywheel with a machinists 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.

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.

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.

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

Locate the axle ID tag on the rear-end housing---usually a sheet-metal tag bolted to the housing, although some vehicles had a paper tag, which may be missing. The metal tag has four different sets of numbers, each grouped in the four corners of the tag. The most important is the model, or service code, found in the upper-left corner. Combine all of the codes, to identify ring-gear size, gear ratio, date and location of manufacture.

Decode the service number by matching it to an axle service code chart, similar to those found on WoodyG.com and Drivetrain. The code chart tells the gear ratio and ring-gear size, denoting an 8- or 9-inch rear end.

Locate the VIN tag on the rear face of the driver-side door---the primary identification tag for the vehicle. On it, look fora box labeled "axle," containing the axle code, which requires consulting a code listing similar to that found on Drivetrain. Verify both the axle tag and door-tag codes to determine whether the vehicle still has its original rear end.

Count the bolts on the rear-end housing, and visually identify the rear-end gasket shape; compare the gasket shape with the chart found on the Drivetrain site (see References section). Ford 7.5s and 8.8s have 10 bolts, the 10.25 has 12 and all Dana units have 10 bolts, but each has a different gasket shape. The chart also provides width dimensions for measurement verification.

Attach a deep socket with an extension to the lower rear-end bolts. According to Ridgecrest, if the socket goes straight on without hitting the case, your vehicle has an 8-inch rear end; if the socket doesnt fit the bolt on the other side of the center, your vehicle has a 9-inch rear end.