KMK NEWSLETTER

OCTOBER 2025

BALL DOOR MODIFICATION

This ball door modification comes from longtime mechanic Jim Banks. Jim discovered that  when he changed the geometry of the springs, he had better functionality with lightweight balls. The change also closes the ball door quickly, reducing the likelihood of pins entering the accelerator box.

NOTE: The ball doors should be adjusted and lubricated before making any changes.

The following instructions are based on Jim’s photos and video posted on Facebook. Please follow all normal safety procedures recommended by the equipment manufacturer.

Doing any modifications to your machines may void your warranty, please investigate before making changes.

1. Lower both sweeps and remove power from both machines.

2. Remove the ball door return springs from both doors.

3. Open the odd lane ball door.

4. Using a power drill and a 1/8-inch drill bit, drill a new hole for the ball door closing spring in the lower flange of the ball door. This hole should be directly below the existing hole in the top flange.

5. Insert 2 each ¼-20X 1 ½ inch bolts into the existing holes in the ball door. These holes are large enough that the bolts can easily be threaded into them using a 7/16 socket and ratchet. Thread the bolts into the holes approximately ¼ inch. Reinstall the ball door closing springs using the configuration shown in the photo below.

6. Restore power to the machines and watch the action of the ball doors with bowling in progress. While this modification works well in most situations, you may easily revert to the OEM configuration if you encounter any ball door problems.

7. When using this modification, the bottom spring may hinder the removal of pins from the accelerator track. Simply remove the spring from the ball door, retrieve the pin and replace the spring.

Try converting a few pairs of ball doors at first, especially any pairs that seem to have problems with lightweight balls. With a little practice, you will be able to convert to this new configuration in 3-4 minutes per pair of lanes. Small changes like this mod can pay big benefits in your overall maintenance program.

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