How to Verify 6202 C3 Bearing Radial Clearance: A Factory Guide for Chainsaw Crankshaft Applications

Published: August 2026 | Technical Article

Why This Matters

In two-stroke chainsaw engines, the crankshaft bearings operate under high rotational speeds and significant thermal expansion. A bearing with insufficient radial clearance will seize when the engine reaches operating temperature — a failure mode that is invisible at the assembly bench but catastrophic in the field.

The 6202 deep-groove ball bearing (15 mm bore × 35 mm OD × 11 mm width) is widely used on chainsaw crankshafts. For this application, C3 (greater-than-normal) radial clearance is mandatory. Yet a large share of field failures trace back to one root cause: bearings labeled or verbally promised as C3 that are actually Normal (CN) clearance.

This guide explains the international standard, the correct measurement method, and the incoming-inspection procedure that prevents this problem.

International Standard: ISO 5753-1

Radial internal clearance for rolling bearings is defined by ISO 5753-1:2017 — Rolling bearings — Internal clearance — Part 1: Radial internal clearance for radial bearings. This standard is harmonized with major national standards worldwide (including GB/T 4604 in China, DIN 620-4 in Germany, and ABMA standards in the United States).

For a bearing with a bore diameter greater than 10 mm and up to 18 mm — which includes the 6202 (15 mm bore) — ISO 5753-1 specifies the following radial clearance ranges:

Key takeaway: A genuine C3 6202 bearing must measure between 0.011 mm and 0.025 mm of radial clearance. Anything measuring 0.003–0.018 mm is Normal clearance and is not suitable for chainsaw crankshaft service.

Note on the overlap: The CN upper limit (18 μm) and the C3 lower limit (11 μm) overlap. A bearing measuring 11–18 μm could technically fall in either group depending on how it was sorted at the factory. This is exactly why the part number suffix and the measurement must both agree — a bearing in the overlap zone labeled only "6202-2RS" is, by default, CN.

Correct Measurement Method (Dial Indicator + Magnetic Base)

This is the method used by bearing manufacturers and OEM engine plants. It is affordable, repeatable, and legally defensible.

Equipment Required

• Magnetic base stand
• Dial indicator with 0.01 mm (10 μm) resolution — a 0.001 mm indicator is preferred for tighter readings
• Fixed mandrel (shaft) matching the 15 mm bore, with a locking nut or collar
• Clean, flat surface

Procedure

1. Stabilize temperature. Perform the test at approximately 20 °C (68 °F). Allow bearings to acclimate to room temperature before measuring.
2. Clean the bearing. Remove all preservative oil and contamination. For 2RS (rubber-sealed) bearings, pry off one seal. The rubber seal lip presses against the inner ring and will artificially restrict outer-ring movement, producing a falsely low clearance reading.
3. Mount the inner ring. Slide the bearing onto the fixed mandrel and lock the inner ring firmly so it cannot move. The outer ring must be completely free.
4. Zero the indicator. Position the dial indicator plunger perpendicular to the outer ring's outer diameter, at the midpoint of the ring width. Set the dial to zero.
5. Measure radial play. Applying a light, consistent force, push the outer ring radially from one side to the other. Record the difference between the maximum and minimum indicator readings — this is the radial internal clearance.
6. Repeat at three angles. Rotate the outer ring by 120° and measure again. Take a total of three readings (at 0°, 120°, and 240°) and calculate the average.

Acceptance Criteria

Cost note: A complete magnetic-base dial-indicator setup costs only a few hundred USD. Testing 5–10 samples per incoming batch is sufficient to detect CN/C3 mixing.

Why Hand-Wiggle Testing Is Not Enough

A common workshop shortcut is to hold the inner ring and wiggle the outer ring radially. This can only detect grossly defective bearings. It cannot distinguish CN from C3:

• Many CN bearings exhibit a slight perceptible play due to normal ball-to-race tolerances.
• The human hand cannot reliably resolve differences of 5–10 micrometers.
• A bearing that feels "smooth" on the bench may still seize once the engine reaches 80–120 °C operating temperature and the rings expand.

Rule: Hand-feel is a screening tool for obvious damage only. It is never a substitute for instrument measurement and never acceptable as a receiving-inspection record.

Why Feeler Gauges Do Not Work for 6202

Feeler gauges are appropriate for large bearings (typically bore diameter above 80–100 mm) where the clearance is large enough to insert a blade. For a 6202 bearing with only 0.011–0.025 mm of clearance, the thinnest standard feeler blade (0.02 mm) is too thick to insert reliably, and the ball path makes access impossible. Do not use feeler gauges on small deep-groove ball bearings.

Part Number Labeling: The #1 Source of Confusion

The Rule

Under ISO and global bearing trade conventions, if the clearance group suffix is omitted, the bearing is Normal (CN) clearance by default.

A supplier's verbal assurance that "these are C3" carries no contractual or technical weight if the label, packing, certificate of conformity, and delivery note all say only "6202-2RS." In the event of a field seizure failure, there is no documentary basis for a claim.

The Correct Full Part Number

The complete, unambiguous designation for a rubber-sealed C3 bearing is:

6202-2RS-C3

The suffix -C3 must appear on:

• The bearing's own etched or laser-marked label (where space permits)
• The individual box / tube packaging
• The certificate of conformity / inspection report
• The delivery note / packing list
• The purchase order

Incoming Inspection Procedure (Ready-to-Use)

Implement this procedure for every 6202 bearing batch:

1. Sampling: Randomly select 5–10 pieces from each incoming batch. For high-risk or new suppliers, increase to 10% of the batch or a minimum of 10 pieces.
2. Documentation check: Verify that the purchase order, delivery note, packaging, and certificate all state C3. If any document omits the C3 suffix, quarantine the batch pending clarification.
3. Seal removal: Pry off one rubber seal from each sample bearing.
4. Measurement: Use the dial-indicator method described above. Take three readings at 120° intervals and average.
5. Decision:
   • Average = 0.011–0.025 mm → Accept for production.
   • Average = 0.003–0.018 mm (CN range) → Reject the entire batch. This is CN bearing supplied as C3.
   • Any reading outside C3 range → Reject and notify supplier.
6. Record: Log each sample's individual readings, the batch/lot number, supplier name, date, and inspector initials. Retain records for the warranty period.
7. Supplier report: Require every shipment to include a radial clearance inspection report listing individual measured values — not merely a checkbox stating "C3."

Common Pitfalls

Third-Party Testing Option

If your facility does not wish to purchase measurement equipment, samples can be sent to an accredited third-party testing laboratory. Typical cost is a few dollars per piece. This is recommended for:

• First batch from a new supplier
• Any batch where documentation is incomplete
• Any batch where field failures have been reported
• High-value or export-critical production runs

Summary

1. Standard: ISO 5753-1 defines C3 radial clearance for 6202 (15 mm bore) as 11–25 μm (0.011–0.025 mm).
2. Label: 6202-2RS without -C3 suffix = Normal (CN) clearance by default. Not for chainsaw crankshafts.
3. Measure: Use a dial indicator on a fixed mandrel, remove one seal, three readings at 120°, average.
4. Inspect: Sample 5–10 per batch; reject the full batch if CN readings appear.
5. Document: Require C3 on PO, packaging, certificate, and delivery note. Require per-piece clearance test reports.
6. Never rely on hand-feel alone.

This article is intended for technical and procurement personnel in engine manufacturing and assembly. For specific application engineering questions, consult the bearing manufacturer or a qualified mechanical engineer.