20Y-27-21210 Final Drive Planetary Gear 31T for Komatsu Excavator

20Y-27-21210 Final Drive Planetary Gear

The 20Y-27-21210 planetary gear works as part of the rotating reduction gear set inside an excavator final drive. Multiple planet gears operate together around the center of the gearbox, sharing travel load while transmitting torque through the reduction stage.

Because these gears work as a matched set, tooth geometry, bore condition and gear width all influence how evenly the load is distributed during excavator travel.

A planetary gear that looks similar from the outside should not be considered interchangeable until the original gear and final drive configuration have been compared.

Planet Gears Share the Travel Load

During travel operation, the planetary gears rotate while remaining supported by the carrier. This arrangement allows several gears to divide the mechanical load rather than concentrating torque on a single gear.

If one gear develops excessive bore wear or tooth damage, the load may no longer be distributed evenly across the set. The remaining gears can then develop accelerated wear even if they initially appear serviceable.

For this reason, the complete planetary stage should be inspected whenever one damaged gear is found.

Check More Than the Tooth Count

Tooth count is an important identification point, but it is not enough by itself to confirm the correct replacement planetary gear.

When comparing the original component, check:

• Outside gear diameter

• Center bore diameter

• Overall gear width

• Tooth profile and working surface condition

• Fit on the carrier pin or bearing

• Final drive configuration and machine serial information

These checks are particularly important on older machines where the installed final drive may have been replaced during previous repairs.

Typical Damage Found During Gearbox Repair

Planetary gears removed from a worn travel gearbox may show several different failure patterns:

• Pitting or flaking on the gear tooth faces

• Cracked or chipped tooth edges

• Uneven contact patterns across the gear width

• Scoring or excessive wear inside the center bore

• Heat discoloration caused by lubrication problems

• Metal debris found in the final drive oil

Repeated damage after a previous repair may indicate a carrier, bearing, alignment or lubrication problem rather than failure of the gear alone.

Verify the Gear Before Ordering

For faster identification, send the following information with your inquiry:

• Excavator model and machine serial number

• Final drive or travel gearbox information

• Clear front and side photos of the original gear

• Confirmed tooth count

• Outside and bore diameter

• Overall gear width

Providing these details helps distinguish similar planetary gears used across different final drive configurations.

Final Drive Gear Support from Topvelsun

Topvelsun supplies replacement planetary gears and related final drive components for excavator repair, rebuilding and parts distribution.

Send us part number 20Y-27-21210 together with your machine and original gear information, and we can help verify the application before quotation.