08-27-2025, 01:47 PM
Problem with Missing Lower Rollers
When a lower roller on a tracked machine—such as an excavator or mini digger—loses its bushings or wears out, the issue isn’t simple to ignore. The bottom rollers (also known as track rollers) bear most of the machine’s weight and ensure that the undercarriage moves smoothly. When rollers are worn, they compromise track alignment and can accelerate wear on other components.
Creative Workaround Approaches
One operator facing this issue couldn’t source a replacement for a Kobelco K909’s lower roller whose bushings were completely gone. Instead of leaving it untouched, several inventive solutions emerged:
Terminology Note
Although some rollers are still available from aftermarket parts suppliers—manufactured to OEM specifications—finding the correct one quickly can be a challenge, especially for older or specialty models.
Typical specs for aftermarket bottom rollers include:
A DIY-minded owner once repaired a mini-digger’s lower roller using a technique of shrinking a steel tube over the worn surface—like fitting a tire over a wheel. By machining the base roller down just past the worn area and sleeve-installing a hardened tube, he restored running diameter with minimal machining and a fast turnaround. This clever workaround transferred the workload to easier-to-source tubular steel, offering a cost-effective interim fix.
Recommended Solutions Overview
Lower roller failure need not ground operations indefinitely. Even when OEM parts are unavailable, operators can apply creativity—whether through bronze bushing fabrication, off-the-shelf hardened tubing, or modified donor rollers. Each method presents trade-offs in longevity, cost, and labor, but all can deliver practical, resourceful solutions in the field. Careful measurement, choice of materials, and retaining lubrication are key to success—letting old machines continue to perform, sometimes better than expected.
When a lower roller on a tracked machine—such as an excavator or mini digger—loses its bushings or wears out, the issue isn’t simple to ignore. The bottom rollers (also known as track rollers) bear most of the machine’s weight and ensure that the undercarriage moves smoothly. When rollers are worn, they compromise track alignment and can accelerate wear on other components.
Creative Workaround Approaches
One operator facing this issue couldn’t source a replacement for a Kobelco K909’s lower roller whose bushings were completely gone. Instead of leaving it untouched, several inventive solutions emerged:
- Custom bushings built at a machine shop—though questions remained about how to retain lubrication within the sealed roller structure.
- Modifying another roller from a different machine to fit, perhaps via machining or adaption.
Terminology Note
- Lower roller (or bottom roller): the undercarriage component that supports the machine’s weight and guides the track.
- Bushing: a sacrificial bearing surface inside the roller that reduces friction.
- Ampco 18: a high-performance copper-based alloy known for resistance to friction and good mechanical properties.
Although some rollers are still available from aftermarket parts suppliers—manufactured to OEM specifications—finding the correct one quickly can be a challenge, especially for older or specialty models.
Typical specs for aftermarket bottom rollers include:
- Material: alloy steels like 50Mn, hardened to HRC 52–58 with deep heat treatment (8–12 mm depth) for extended wear life.
- Features: forged shells, sealed bearings, bronze bushings, and OEM-caliber dimensions.
A DIY-minded owner once repaired a mini-digger’s lower roller using a technique of shrinking a steel tube over the worn surface—like fitting a tire over a wheel. By machining the base roller down just past the worn area and sleeve-installing a hardened tube, he restored running diameter with minimal machining and a fast turnaround. This clever workaround transferred the workload to easier-to-source tubular steel, offering a cost-effective interim fix.
Recommended Solutions Overview
- Locate OEM or aftermarket replacement rollers, verifying part numbers and ensuring material specs match—check hardness, flange type, and bearing seal specs.
- Fabricate replacement bushings from suitable alloy (e.g., Ampco 18), retaining oil seals or bearings as needed.
- Sleeve-wrapping approach: machine worn roller slightly undersize, shrink-fit a precision-cut hardened steel tube over it, then turn or grind to correct diameter.
- Use parts from different models, adapting by machining or modifying rollers to fit the specific undercarriage layout.
- Measure accurately the roller's diameter and flange configuration to ensure fit.
- Always use heat-treated, wear-resistant materials for any fabricated component.
- Ensure proper sealing or lubrication pathways remain intact post-fabrication—rollers must retain grease for continued function.
- Retain a rotating spare or used “parts” machine to act as a donor for future emergencies.
Lower roller failure need not ground operations indefinitely. Even when OEM parts are unavailable, operators can apply creativity—whether through bronze bushing fabrication, off-the-shelf hardened tubing, or modified donor rollers. Each method presents trade-offs in longevity, cost, and labor, but all can deliver practical, resourceful solutions in the field. Careful measurement, choice of materials, and retaining lubrication are key to success—letting old machines continue to perform, sometimes better than expected.
