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Ball Bearing (bearing) KBC 6304DDC3G81 - 20 × 52 × 15 mm
$5.99
Ball Bearing (bearing) KBC 6304DDC3G81 - 20 × 52 × 15 mm
Description
KBC sealed ball bearing for pool and spa pump motors. Medium-duty 6304 series, double rubber seal and C3 internal clearance — the front bearing (pump side) of most North American-made 1.5 to 3 HP motors.
Decoding the 6304DDC3G81 reference
| Segment | Meaning |
|---|---|
| 6304 | Deep groove ball bearing, 6300 series (medium load) — 20 mm × 52 mm × 15 mm |
| DD | Double contact rubber seal, both sides (equivalent to 2RS) |
| C3 | Increased internal clearance |
| G81 | KBC factory grease code — specific electric motor filling |
Who is KBC
KBC is a Korean manufacturer founded in 1953, now owned by Schaeffler Korea — the group behind FAG and INA. ISO 9001 and ISO/TS 16949 (automotive standard) certified, with factories in Changwon, Jeonju, and Ansan. This is not a generic bearing: it is original equipment quality, supplied to automobile manufacturers and electric motor manufacturers.
Caution: 6304 or 6204?
Both have a 20 mm bore and look similar on a shelf. What distinguishes them is the outside diameter:
| Reference | Bore | Outside diam. | Thickness |
|---|---|---|---|
| 6304 (this one) | 20 mm | 52 mm (2.047 in) | 15 mm (0.591 in) |
| 6204 | 20 mm | 47 mm (1.850 in) | 14 mm (0.551 in) |
Five millimeters apart on the outside: the 6204 will spin freely in a 6304 housing and destroy the motor housing. Measure the outside diameter or read the engraving on the bearing you are removing.
Technical specifications
- Type: deep groove ball bearing, single row, 6300 series
- Dimensions: 20 mm (0.787 in) × 52 mm (2.047 in) × 15 mm (0.591 in)
- Sealing: double contact rubber seal (DD / 2RS)
- Internal clearance: C3 (increased)
- Dynamic load: approx. 15.9 kN (≈ 3,570 lb)
- Static load: approx. 7.65 kN (≈ 1,720 lb)
- Weight: approximately 144 g (5.1 oz)
- Materials: 52100 chrome steel, stamped steel cage
- Operating temperature: up to approximately 120 °C
- Lubrication: factory lifetime greased — no maintenance
Why C3 on a pump motor
A motor that runs 8 to 12 hours a day heats up and expands its shaft, which tightens the bearing. Without extra clearance, the bearing forces, overheats, and fails. The C3 clearance absorbs this expansion and keeps the bearing free when hot. It is the standard specification of pump motor manufacturers — a normal clearance bearing will not last the season.
Where does this bearing go in your motor
On most pump motors, the 6304 is the front bearing, pump side, the one that takes the thrust of the turbine — hence the sturdier format of the 6300 series. The rear bearing, fan side, is most often a 6203 (17 × 40 × 12). Check both before ordering: some motors use the same format twice, others do not.
Signs you need to replace your bearings
Continuous rumbling or whistling, squeaking on startup, vibrations in the pump housing, abnormally hot motor, or shaft hard to turn by hand once the motor is unplugged. A worn bearing that is not replaced stores the shaft and eventually burns the stator — a $40 repair becomes a complete motor replacement.
Installation tip
Replace the two bearings at the same time: they have accumulated the same hours. Take advantage of the disassembled motor to also change the mechanical seal — it is often a leak at the seal that flooded the front bearing in the first place.
Compatibility
Suitable for pool and spa pump motors using a 6304 bearing, especially A.O. Smith / Century / Regal Beloit and Emerson / US Motors 1.5 to 3 HP motors mounted on Hayward, Pentair, Sta-Rite, and Jacuzzi pumps. Equivalents: 6304-2RS-C3, 6304DDU-C3, 6304-2NSE-C3, 6304-LLU-C3. Confirm by the reference engraved on your existing bearing or by the catalog number of your motor.
