Bearing Drift Protection Plate

The final millimeter of a bearing install is where things get destroyed. The drift has driven the bearing nearly home, the outer race is flush with the shell shoulder, and one more press stroke is supposed to seat it. Without a protection plate between the drift and the bearing, that last stroke can scuff the bearing's seal lip, deform the dust shield, or contact the inner race instead of the outer race. The seal damage often doesn't show up until the bearing is running on the bike and the first contaminant gets past the lip. The 1721.2 is the dedicated protection plate that sits between drift and bearing on the final strokes of a press install.

How it works

The plate is a hardened-steel washer-form interface that drops over the bearing's outer race before the drift comes down for the final seat. It does three things at once:

1. Spreads load across the full outer-race face. A drift sized slightly smaller than the bearing OD concentrates press force on a partial circumference; the protection plate evens it out across the full outer race.
2. Stands off the seal lip. The plate's bore is sized to clear the bearing seal, so even if the drift sits proud of the bearing face the plate keeps the press load off the seal.
3. Stands off the inner race. Press load on a cartridge bearing must stay on the outer race only. The plate's geometry makes it physically impossible for the drift to touch the inner race during the final press stroke.

When to use it

Use the protection plate on the last one or two strokes of every bearing install. The earlier strokes (when the bearing is half-engaged or less) can use the drift directly, since the bearing is still moving freely through the bore and seal damage isn't yet possible. The risk window is the final seating, where the bearing is bottomed against the shell shoulder and the drift's force has nowhere else to go.

Spec

• Material: hardened tool steel
• Face geometry: ground flat to within press tolerance
• Compatibility: sits between any drift in the 1721 set and the bearing being pressed

Compatibility

The 1721.2 fits the Unior Bearing Press 1721 family and the related Over Axle Bearing Press Set. The plate's inner-race clearance is sized to current-generation 6000-series, 6800-series, and 6900-series bearings; the same plate covers the BB bearing range. The replacement drift set 1721.1 is the sized drift; the protection plate is the universal interface that sits between drift and bearing.

Built in Zreče, Slovenia

Unior has been forging hand tools in Zreče since 1919, and is the official technical partner of multiple World Tour and downhill teams. The protection plate is one of those small parts that doesn't change the press's headline spec but shows up in the bearing's working life. A bearing pressed home with seal damage fails at the seal months later; pressed with the protection plate in place, the seal lives as long as the bearing does.

Pro tip from our mechanics

We mark the protection plate's “up” side with a paint pen so it always goes onto the bearing the same way. The plate's face that contacts the bearing is the one that's been ground flat to spec; the opposite face is the one that takes the drift. Reversing the plate works mechanically but means alternating which face takes the contact wear, and the first face stays in spec longer if it's always the bearing side. Where this fits in the install sequence: Bearing and headset service: a workshop guide →