How to Shim a Starter Motor Like a Pro

Getting your starter motor to engage properly can be a frustrating experience, often resulting in a frustrating "click" instead of the satisfying roar of the engine. One common solution to this problem is shimming the starter motor. This seemingly simple task requires precision and understanding, and doing it correctly can save you time, money, and a lot of aggravation. This guide will walk you through the process, transforming you from a frustrated car owner into a starter motor shimming pro.

Why Shim a Starter Motor?

Before diving into the how-to, let's understand why shimming is necessary. The starter motor's pinion gear needs to perfectly mesh with the engine's flywheel ring gear to crank the engine. If the distance is off—even slightly—the pinion gear won't engage properly, leading to that dreaded clicking sound. Common causes of this misalignment include:

• Worn engine mounts: Over time, engine mounts can sag, altering the engine's position relative to the starter motor.
• Bent starter motor mounting bracket: An impact or accident can bend the bracket, pushing the starter motor out of alignment.
• Worn flywheel ring gear: Excessive wear on the ring gear can also contribute to engagement problems.
• Incorrect installation: Improper installation of the starter motor can also result in misalignment.

Shimming provides the necessary adjustment to restore proper engagement.

What You'll Need

Before you begin, gather the following tools and materials:

• Shims: These are thin metal plates of varying thicknesses. You'll likely need a few different thicknesses to find the perfect fit. These are often available at auto parts stores. Don't substitute anything; use proper shims.
• Socket set: A variety of sockets will be necessary to remove and install the starter motor.
• Wrench(es): Depending on the starter motor's mounting bolts, you might need open-ended or box-end wrenches.
• Screwdriver(s): Possibly needed to remove any access panels or components obstructing the starter.
• Jack and jack stands (recommended): Safely lifting the vehicle will make access easier and safer.
• Gloves: Protect your hands from grease and grime.
• Torque wrench: Essential for tightening the starter motor bolts to the manufacturer's specifications to avoid damage. This prevents both over-tightening and under-tightening.
• Pen or marker: To mark the shims' position and thickness for future reference.

Step-by-Step Shimming Process

1. Disconnect the Battery: This crucial step prevents accidental shorts and protects you from electrical shock. Disconnect the negative terminal first.

2. Access the Starter Motor: Locate the starter motor and carefully remove any access panels or components that obstruct your access. This often involves removing parts like splash shields or air intake components.

3. Remove the Starter Motor: Carefully remove the starter motor's mounting bolts and disconnect any electrical connectors. Note the position and orientation of the starter motor before removal.

4. Assess the Situation: Carefully examine the starter motor and its mounting bracket for any signs of damage or misalignment. Note how much space exists between the pinion gear and the flywheel ring gear. This visual inspection is crucial for understanding the extent of the adjustment needed.

5. Install Shims: Carefully place the shims between the starter motor and its mounting bracket. Experiment with different combinations of shim thicknesses until the pinion gear engages smoothly with the flywheel ring gear.

6. Test and Reinstall: Reconnect the starter motor's electrical connectors, carefully reinstalling the unit. Make sure everything is correctly positioned and the wiring is securely connected.

7. Test the Engagement: Reconnect the battery, and try cranking the engine. Listen carefully for any signs of grinding or clicking. If necessary, adjust the shims further. It may require multiple attempts to find the correct shim thickness.

8. Tighten Securely (with Torque Wrench): Once the correct shim thickness is found and the starter engages smoothly, tighten the mounting bolts using a torque wrench to the manufacturer’s specified torque setting. This is critical to prevent damage and ensure the proper seating of the starter.

9. Reassemble: Carefully reinstall any access panels or components you removed earlier.

10. Test and Verify: Test start the vehicle and verify the starter now engages without issue.

Troubleshooting: Starter Still Not Engaging

• Check the Battery: Ensure the battery is fully charged and providing sufficient power.
• Inspect the Solenoid: The solenoid may be faulty, preventing the pinion gear from extending.
• Examine the Flywheel Ring Gear: A severely worn ring gear might require replacement, negating the effectiveness of shimming.
• Check Wiring Connections: Ensure all electrical connections are clean and tight.

Can I Use Washers Instead of Shims?

No. While washers might seem like a suitable substitute, they are not designed for this application and may not provide the necessary precision or durability. Using incorrect materials could lead to premature starter failure or damage to the vehicle. Always use shims specifically designed for starter motor adjustments.

This detailed guide will empower you to tackle starter motor shimming with confidence. Remember that safety and precision are paramount. If you're unsure about any step, it's best to consult a qualified mechanic.