Excavator Lock Pin Stuck? Avoid Costly Repairs When Changing Attachments

The hydraulic quick coupler on a Komatsu PC490LC Excavator comes with a lock pin. It’s a simple device for extra safety.

Most excavators include some sort of lock pin in their hydraulic quick couplers.

Have you ever had problems with an excavator lock pin stuck? It was likely due to changing your attachment incorrectly.

We’ve seen three common mistakes among operators when changing attachments, and we want to show you how to avoid them, whether you own a Komatsu PC490LC or another make and model.

When the lock pin is stuck, chances are someone tripped the switch of the wedge bar control to the unlocked position, making the hydraulics push the wedge against the lock pin.

The solution is as simple as getting the switch back to the locked position so the wedge goes back into place to hold the bucket. The wedge control switch is on the right-hand side of the cabin.

Next, lay the bucket entirely on the ground and try again to pull out the lock pin. It should be loose, meaning the wedge coupler and the bucket lugging fit correctly.

The role of the pin is to keep the wedge from coming back in the event of a hydraulic failure or if the operator trips the switch accidentally.

The pin is an extra layer of security, so we recommend always keeping it in place during operation, even though the hydraulics will hold the attachment.

Never try pulling out the lock pin with the attachment off the ground. If a hydraulic failure occurs, the attachment can suddenly fall, hurting you or other bystanders.

The lock pin itself is held in place by a safety pin. People usually lose the safety pin when taking out the lock pin. We recommend locking them together and keeping them in a visible and safe place.

If you try to release the bucket without waiting for the wedge to return, two problems can occur:

1. You can chip the wedge or the lugging.
2. There’ll be friction between the wedge and the lugging overstressing pins or the hydraulic system.

The wedge lasts 15 to 20 seconds to retract or engage when you activate the control switch.

You’ll hear a beeping sound when you disengage the wedge (control switch in the unlocked position). The warning will continue until you return the switch to the locked position to bring the wedge toward the attachment.

There’s a clearance between the wedge and the lugging to ease attachment and detachment. The wedge and lugging shall only contact each other at the wedge’s top and lugging’s bottom faces, and the only force between them must be pressure (see the picture below).

Installing an attachment without letting the wedge retract will also cause problems:

• You can chip or bend the wedge or damage the lugging.
• You can build up pressure in the hydraulic fluid, damaging cylinders or hoses.

We recommend turning down the RPM (Revolutions Per Minute) when changing attachments.

The RPM control on an excavator primarily regulates the engine speed or throttle of the machine (the rate at which the engine’s crankshaft rotates).

Lowering the RPM provides better control over the excavator’s movements during attachment changes. It ensures the attachment aligns properly with the excavator’s coupler while preventing accidents for the operator and those nearby.