Starter Shim Adjustment
Learn how to properly shim a starter motor to correct gear mesh, eliminate grinding noises, and prevent ring gear damage.
Tools Needed
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Instructions
Identify the Problem
Grinding or whirring on startup (but the engine cranks) usually means the starter pinion gear is not meshing properly with the ring gear. Shimming corrects the gap.
Access the Starter
Disconnect the battery negative. Raise and support the vehicle if needed for access. Remove the starter wires and mounting bolts.
Inspect the Ring Gear
With the starter removed, inspect the flywheel ring gear through the opening. Look for chipped, worn, or damaged teeth that indicate chronic misalignment.
Understand Shim Function
Shims are thin metal spacers placed between the starter mounting face and the bell housing. Adding shims moves the pinion away from the ring gear; removing them moves it closer.
Test Fit with Shims
Start with one shim on the outer bolt hole. Reinstall the starter temporarily and crank the engine briefly. If grinding continues, try one shim on the inner hole instead.
Find the Sweet Spot
The correct shim configuration produces a clean, quiet engagement. Too close = grinding. Too far = whirring without full engagement. Adjust one shim at a time.
Final Install
Once correct mesh is achieved, torque all starter bolts to spec with shims in position. Reconnect all wiring and the battery. Test several cold and warm starts.
