One thing to remember when picking a flexplate for a small block Chevy (SBC) is that the 1986 and newer Chevy small block engines require a weighted flexplate to help keep the vibration out of the engine. If you bolt an old style neutral balanced flexplate to an engine when it requires a weighted flexplate, you will feel considerable vibration from the engine. The weighted flexplate has 14 1/2-inch diameter and 168 teeth, and requires an offset bolt pattern starter. The smaller flexplate has a 12 3/4-inch diameter and uses a starter with the two bolts adjacent to each other.
Determine the flexplate needed. Count the teeth on the flexplate to be replaced. If it has 168 teeth it is the larger one. The other choice is a 153-tooth plate. If you don't have a flywheel on the engine and the engine is 1986 or newer, it needs the larger-weighted flexplate.
Select the flexplate manufacturer. If the vehicle is expected to last a long time, then use a high quality GM replacement flexplate. The GM original equipment flexplate is more expensive. If the vehicle has a low life expectancy, then the purchase of a used or aftermarket flexplate should suffice.
Inspect and clean any used flexplate with spray brake cleaner before purchasing it. Check for hair line cracks in and around the crank bolt holes and be sure the teeth are clean and not worn.
Match up the flexplate with the proper starter. The 168-tooth flexplate uses a starter that has bolt holes in the mount that are offset or staggered. The smaller plate uses a starter with mount holes that are adjacent to each other
