Case Study 2: Uncovering Oil Seal Walk-Off Through Gemba

Case Study 2: Uncovering Oil Seal Walk-Off Through Gemba 

1 Introduction

Oil seals are critical components in automotive and industrial applications, preventing

fluid leaks and contamination in assemblies like wheel bearings. When failures occur,

they can lead to significant downtime, repair costs, and potential recalls. This case study

examines a persistent oil seal failure in a wheel bearing assembly at an original equip-

ment manufacturer (OEM), highlighting the importance of systematic failure analysis

and shop floor engagement in identifying root causes.

2 Background

The OEM, a leading manufacturer of agricultural equipment, reported unexpected “walk-

off” failures of oil seals immediately after assembly into wheel bearing blocks. The seal

design, in production for nearly a decade, was well-established, rigorously tested in both

laboratory and field conditions, and had no prior history of issues. The sudden failures

prompted the customer to suspect a material defect, demanding an immediate switch to

a different compound variant to maintain production schedules.

3 Initial Response

Eager to preserve the customer relationship, management approved the material change,

using an existing compound variant to bypass validation testing. After two weeks, new

seals were molded and installed. However, the walk-off issue persisted, indicating that

the material was not the root cause.

4 Failure Analysis Process

A structured failure analysis was initiated, involving sample examination, process au-

dits, and stakeholder interviews. A critical observation emerged: the OEM operated two

plants, but only one reported the issue, while the other experienced no failures. This dis-

crepancy suggested a plant-specific factor.

During a Gemba walk on the affected plant’s assembly line, an operator casually commented  that the

new bearing “felt heavier.” Further investigation with operators, plant staff, and the

design team revealed that the assembly had been redesigned for a new, more powerful

tractor variant, requiring a bearing 10% larger than the original. Due to cost and techni-

cal constraints, the same housing was retained, and the larger bearing was press-fitted.

The unchanged bill of materials (BOM) and assembly instructions led operators to apply

the same grease volume as with the smaller bearing. The larger bearing reduced the

1housing’s internal volume, causing overfilling. During assembly, the seal compressed

the grease, and upon load removal, the expanding grease dislodged the seal, resulting

in walk-off.

5 Solution

The root cause identified, the OEM updated the BOM and assembly instructions to adjust

grease volume for the new bearing size. This ensured adequate space for the seal to seat

securely, eliminating the walk-off issue.

6 Lessons Learned

• Systematic Failure Analysis is Essential: Initial assumptions about material defects

led to wasted time and resources. A structured approach, including data collection

and process audits, pinpointed the true cause.

• Gemba Walks Uncover Critical Insights: The operator’s comment during the shop

floor observation was pivotal. Engaging frontline workers can reveal details missed

in high-level reviews.

• Small Changes, Big Impacts: Overlooking the grease volume adjustment for a re-

designed bearing caused significant failures, underscoring the need to review all as-

pects of a design change.

7 Conclusion

This case demonstrates the value of thorough failure analysis in resolving complex man-

ufacturing issues. By combining Gemba walks, stakeholder collaboration, and data-

driven investigation, the OEM resolved the oil seal walk-off problem and prevented fu-

ture failures. For industries reliant on precision components like oil seals, adopting sys-

tematic failure analysis protocols and fostering shop floor engagement are critical to

ensuring reliability and minimizing costs.