How to Balance a Chevy Small Block 383 External Balance & Crank


Particular attention needs to be paid to the balance of the crankshaft for the 383 small-block Chevy stroker combination. Originally, the 383 stoker crank was not internally balanced and required a harmonic balancer and flex plate with counterweights. Today, aftermarket cranks for the 383 stroker are available in either internally or externally balanced designs, so it's important to use the correct balancer and flex plates. Balancing the crankshaft requires specialty equipment, so an engine machine shop will need to complete this task.

Things You'll Need

  • 3.75-inch stroke SBC crankshaft
  • Harmonic balancer/flexplate
  • Connecting rods and pistons
  • Bearings, rings and piston pins
  • Scale
  • Purchase the crankshaft, connecting rods, pistons and pins, rings and bearings, and harmonic balancer and flex plate for the intended level of performance of the 383 engine being built. Note that the balancer and flex plate must match the intended "type" of balance the crankshaft is manufactured with: internal versus external. Aftermarket 383 cranks come in either type. For extreme performance usage, such as a competition race engine, an internally balanced crankshaft is preferred.

  • Take the entire rotating assembly to a machine shop. Various combinations of crank counterweight design and connecting rod/piston weight will vary, so no complete assembly will have exact balance unless it is weighed, spun and machined. Provide the machinist with the intended usage of the engine: standard, high or racing-performance. From there, the machinist will weigh all parts separately.

  • The machinist will weigh and record each piston, pin, rod, bearings and set of rings separately. Each piston/rod assembly -- along with bearings, rings and pin plus an allowance for oil -- is organized to match the lightest piston first, and then the others are machined to match the lightest weight. Next, the rods are also ground to reduce their weight to match the lightest one. Each complete piston/rod assembly will typically be within 1 g of each other.

  • Place the crankshaft into the saddle of the electronic balancer beneath the mill. Attach the flex plate and harmonic balancer on the crankshaft and tighten. Spin the crank in the balancer to identify areas of imbalance. Remove enough metal with the mill by drilling holes in the crank counterweights until the proper balance for the piston/rod assemblies being used is reached.

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