Xe máy Industry Bearings: Codes & Applications

Motorcycle bearings are rolling elements — ball bearings for wheel hubs and engine positions, tapered roller bearings for steering heads — installed in wheel hubs, steering heads, engine crankshafts, camshafts, and gearboxes of two-wheel vehicles — covering everything from commuter scooters and underbone bikes to sport bikes and large-displacement touring motorcycles.

Vietnam's motorcycle market exceeds 3.5 million units annually, with an aftermarket service network spanning tens of thousands of repair shops. At these volumes, selecting the correct bearing code — matching seal type, internal clearance class, and dimensional series — directly determines engine longevity and rider safety. This article covers each installation position, standard bearing codes with full specifications, and brand selection criteria based on ISO 492 and original equipment documentation.

What are motorcycle bearings?

Motorcycles place extreme demands on compact bearings: wheel hubs carry combined radial and axial loads through rough road surfaces, steering heads transmit impact loads from the front fork, crankshaft bearings must survive high-RPM cyclic loading with minimal oil film thickness, and gearbox needle rollers operate under shock loads during gear shifts.

Bearing failures in motorcycles have direct safety consequences — a seized front wheel bearing or a failed steering head bearing causes loss of directional control. Understanding the four major installation groups prevents mismatched replacements:

Wheel hub bearings

Front and rear wheel bearings carry combined radial load (rider and vehicle weight) and axial load (cornering forces), while also absorbing road shock. The 2RS double-sealed type is mandatory for this position — wheel hubs are exposed to water, road grit, and mud that would rapidly destroy an open or single-shielded bearing.

Bearing code selection depends on engine displacement and vehicle class:

• 6301-2RS (d=12, D=37, B=12 mm, C=7.65 kN, C₀=3.45 kN) — front wheel on lightweight commuters: Honda Wave Alpha, Honda Future 125; weight class under 120 kg
• 6302-2RS (d=15, D=42, B=13 mm, C=11.4 kN, C₀=5.40 kN) — front and rear wheels on 125cc automatic scooters: Honda Air Blade, Yamaha NVX; most common code in Vietnamese aftermarket
• 6303-2RS (d=17, D=47, B=14 mm, C=13.5 kN, C₀=6.55 kN) — rear wheel on 150–155cc sport underbone bikes: Yamaha Exciter 155, Honda Winner X; higher radial load from acceleration forces
• 6304-2RS (d=20, D=52, B=15 mm, C=15.9 kN, C₀=7.80 kN) — both wheels on 200–250cc sport bikes and naked bikes: Yamaha MT-15, Honda CB150R

A critical installation detail: wheel bearings must be seated with a bearing press or a tube driver that contacts only the outer ring. Hammering the inner ring to seat the outer ring transfers force through the rolling elements, creating brinelling on the raceway and destroying the bearing immediately. Correct axle nut torque after installation is equally important — both undertightening (allowing axial play) and overtightening (preloading the outer ring against the hub spacer) accelerate bearing wear.

Seal type matters: 2RS (rubber contact seals) provides maximum protection against water and contamination. The alternative 2Z (metal shields) is acceptable only in dry, low-contamination environments — not recommended for Vietnamese road conditions with frequent rain and unpaved surfaces.

Steering head bearings

The steering head carries combined radial and axial loads from fork flex during braking, and intermittent shock loads from road bumps transmitted through the front wheel. This position requires tapered roller bearings (TRB), which handle combined loading more effectively than deep groove ball bearings.

Standard codes for Vietnamese motorcycles:

• 30204 (d=20, D=47, B=15.25 mm, C=25.2 kN, C₀=28.5 kN) — lower steering head on 125–150cc underbone bikes: Honda Wave series, Yamaha Sirius
• 30205 (d=25, D=52, B=16.25 mm, C=29.0 kN, C₀=33.5 kN) — upper and lower steering head on 150–250cc motorcycles; upper bearing typically paired with a lighter-duty version
• 32005 X (d=25, D=47, B=15 mm) — alternative configuration on sport bikes where lower steering profile is required; lighter construction, lower axial load capacity

TRB pairs at the steering head must be installed with correct preload. Insufficient preload allows axial play — the handlebars feel loose at center and the bike wanders at highway speeds. Excessive preload increases steering effort and creates a notchy center feel. Adjustment procedure: tighten the steering stem nut to remove play, then back off slightly until the steering moves freely through full lock without resistance.

Failure signs: notchy or rough feel when slowly turning handlebars, click or clunk when braking hard (axial play), heavy steering effort at low speed. Replace in pairs — replacing one cone while leaving a worn cup leads to uneven load distribution and early failure of the new bearing.

Engine bearings: crankshaft and camshaft

Crankshaft bearings

Crankshaft bearings operate under the most demanding conditions in the motorcycle: high cyclic loads from combustion pressure, rotational speeds of 1,000–10,000 rpm, and a thin oil film that must not be disrupted by thermal expansion. Internal clearance class C3 (greater than standard) is mandatory — standard C0 clearance tightens under thermal expansion and causes seizure.

Common codes by engine displacement:

• 6204 C3 (d=20, D=47, B=14 mm, C=12.7 kN, C₀=6.55 kN) — crankshaft main bearing on 100–110cc 4-stroke engines: Honda Wave 110, Honda Future 110; C3 clearance mandatory
• 6205 C3 (d=25, D=52, B=15 mm, C=14.8 kN, C₀=7.80 kN) — the most widely used crankshaft code in Vietnam's 125cc market: Honda Air Blade 125, Yamaha Nouvo; C3 mandatory
• 6206 C3 (d=30, D=62, B=16 mm, C=19.5 kN, C₀=11.2 kN) — crankshaft on 150–155cc engines: Yamaha Exciter 155, Honda Winner X; higher load rating for larger stroke and bore

The difference between C3 and standard (C0) clearance is 8–13 μm on radial internal clearance. At operating temperature, the crankshaft expands outward and the bearing housing expands inward — C3 clearance accommodates this differential expansion while maintaining the minimum oil film required for hydrodynamic lubrication. Installing C0 bearings on a crankshaft causes premature failure within the first 20,000–30,000 km.

Camshaft bearings

Camshaft bearings operate at lower loads than crankshaft bearings — driven at half crankshaft speed and loaded primarily by valve spring pressure rather than combustion. The 2RS sealed type is used here to retain camshaft oil splash lubrication and prevent contamination.

Common codes:

• 6001-2RS (d=12, D=28, B=8 mm, C=5.10 kN) — camshaft on 100–110cc engines
• 6002-2RS (d=15, D=32, B=9 mm, C=5.60 kN) — camshaft on 125cc engines; the most common replacement code in this segment
• 6003-2RS (d=17, D=35, B=10 mm, C=6.00 kN) — camshaft on 150–155cc engines

Camshaft bearing replacement intervals are longer than crankshaft — typically 60,000–80,000 km with correct oil change intervals (every 3,000 km with mineral or 5,000 km with synthetic). Early failure is almost always caused by oil starvation from extended oil change intervals or incorrect viscosity grade.

Gearbox bearings: needle rollers and DGBB

Motorcycle gearboxes operate submerged in shared engine oil (wet-clutch designs) or dedicated gearbox oil. The compact packaging of motorcycle transmissions requires bearings with maximum load density — needle rollers dominate the lay gear positions, while DGBB handles the shaft ends and shift drum.

Needle roller bearings for gear shaft positions:

• HK1212 (d=12, D=16, B=12 mm, C=8.5 kN) — 2nd and 3rd gear lay positions on 110cc gearboxes; drawn-cup type
• HK1516 (d=15, D=21, B=16 mm, C=13.0 kN) — gear lay positions on 125–150cc gearboxes; standard code across Honda and Yamaha platforms
• NK17/16 (d=17, D=25, B=16 mm, C=14.2 kN) — machined outer ring version for positions requiring press-fit outer ring; higher dimensional precision than HK series

Needle rollers do not carry axial load — every needle roller position is paired with a thrust washer or a separate ball bearing for axial force management. Replacing only the needle without replacing the worn thrust washer causes early failure.

Deep groove ball bearings for shaft ends and shift drum:

• 6004-2RS (d=20, D=42, B=12 mm, C=9.36 kN) — output shaft bearing on 125cc gearboxes
• 6005-2RS (d=25, D=47, B=12 mm, C=11.2 kN) — secondary shaft bearing on 150cc gearboxes
• 6204-2RS (d=20, D=47, B=14 mm, C=12.7 kN) — shift drum bearing on manual-clutch gearboxes (125–150cc sport bikes)

Gearbox bearing replacement requires engine or gearbox case splitting — significant labor cost that justifies using quality branded bearings from the start. Installing counterfeit needle rollers (mismatched roller diameter or incorrect hardness) causes immediate scoring of the gear bore.

NTN, NSK, ZVL for motorcycle aftermarket

The three most widely distributed motorcycle bearing brands in Vietnam are NTN (Japan), NSK (Japan), and ZVL (Slovakia/EU).

NTN is the factory supplier to Honda Vietnam for most OEM bearing positions — crankshaft, camshaft, and wheel hub bearings on Wave, Air Blade, and Future models carry NTN part numbers. This makes NTN the natural choice for Honda aftermarket replacement: exact dimensional compatibility, identical clearance class, and matching grease specification. NTN identification: NTN 6205 C3, NTN HK1516.

NSK is the primary OEM supplier to Yamaha Vietnam and Suzuki — Exciter, NVX, and Winner X crankshafts frequently specify NSK bearings. NSK's motorcycle product line is narrower than NTN's in Vietnam's aftermarket distribution network, but availability for Yamaha-specific codes (6303-2RS, 6206 C3) is generally good through official distributors. NSK identification: NSK 6303 DDU (= 2RS equivalent), NSK 6206 CM C3.

ZVL manufactures to ISO 492 and EU dimensional standards, with dimensional interchangeability across all DGBB and needle codes used in motorcycle applications. ZVL is positioned as Tier 1 for standard positions where OEM brand matching is not required — independent repair shops use ZVL for wheel hub bearings, steering head TRBs, and camshaft replacements with consistently reliable results. ZVL offers competitive European pricing versus Japanese brands without sacrificing load ratings or seal quality. ZVL identification: ZVL 6205-2RS/C3, ZVL 30205.

Counterfeit detection is a critical concern for motorcycle bearings in Vietnam, where counterfeit NTN and NSK wheel bearings are widespread. Counterfeit identification signs: uneven or shallow laser engraving on the shield or outer ring; gritty feel when rotating slowly by hand before installation; excessive axial play even in a new bearing; packaging with blurred fonts or incorrect model number formatting (NTN uses format "6205 C3", never "6205-C3"). Purchase from authorized distributors only — counterfeit bearings at wheel hub positions fail catastrophically, not gradually.

Case study: repair workshop in Gò Vấp

At a motorcycle repair workshop in Gò Vấp district, Ho Chi Minh City, a technician received a 2019 Honda Air Blade 125 with a complaint of unusual noise from the rear wheel that increased with speed and was not affected by braking or acceleration.

Diagnosis: Lifted the rear wheel, rotated by hand — detected a grinding, rough feel confirming bearing damage. Checked axial play: approximately 0.8 mm, exceeding the acceptable limit of 0.3 mm. Conclusion: rear wheel bearing failure, most likely the drive-side bearing.

Bearing code: Air Blade 125 rear wheel uses 6302-2RS (d=15, D=42, B=13 mm) for the drive side. The workshop's stock had 6302-ZZ (metal shields) instead of 2RS (rubber seals).

Challenge: The supplier had 6302-ZZ available but not 6302-2RS. The technician understood that 6302-ZZ is dimensionally identical but uses metal shields rather than rubber contact seals — providing significantly lower protection against water and grit ingress at the wheel hub.

Decision: The technician declined the 6302-ZZ substitution and sourced 6302-2RS from a second supplier. Simultaneously inspected the opposite wheel bearing — the non-drive side 6302-2RS showed some roughness and was replaced as a precaution (pair replacement reduces the probability of a second failure within a few months).

Outcome: The rear wheel ran smoothly, and the replacement pair showed no recurrence over 6 months of follow-up. The technician noted that an earlier repair on a different vehicle where 6302-ZZ had been installed as a substitute lasted less than 8,000 km before water ingress caused corrosion and failure.

Key lesson: seal type is not interchangeable for wheel hub positions. 2RS and 2Z use the same dimensions and load ratings but differ fundamentally in contamination protection. Vietnamese riding conditions — wet roads, unpaved surfaces, water crossings — require 2RS rubber seals at all wheel positions.