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newSchoolWorks.com › VoTechWorks › Manufacturing & Marine › Industrial Maintenance › Bearings: Selection, Installation, Lubrication, and Failure Analysis › Lesson 5
MFG-INDU16-03 · Lesson 5 · 13 clock hours · lab

Lubrication Hands-On: Greasing, Oil Changes, and Contamination Control

Objective. Students will correctly grease a pillow-block bearing, perform an oil-bath level check and drain-and-refill on a gearbox training unit, and prevent contamination using proper handling and purge procedures.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed engineer or certified journey-level tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Why Proper Lubrication Procedure Matters

A bearing can be perfectly selected and installed, yet fail within weeks if lubrication is applied incorrectly or if contamination enters the housing. Studies of bearing failures consistently show that inadequate lubrication and contamination together account for the majority of premature bearing failures in industrial settings. This lab puts the correct procedures in your hands so that calculation and theory become reliable shop habit.

Safety Before You Begin

Always apply lockout/tagout (LOTO) to any machine before servicing its bearings or gearbox — confirm zero energy state with a try-start before touching the equipment. Wear nitrile gloves throughout: lubricant additives and used oil can carry metal particles and chemical hazards. Lay spill absorbent pads under drain points before opening any plug. Dispose of used oil and contaminated grease in labeled waste containers per your facility's environmental procedures — never pour either down a drain.

Activity 1 — Manual Greasing of Pillow-Block Bearings

Calculating and counting strokes. A standard manual grease gun delivers approximately 1 gram of grease per stroke, though this varies slightly by gun and grease consistency; always verify your specific gun's output during training. You calculated the required grease quantity in Lesson 4 using the formula based on bearing bore diameter. Convert that mass to a stroke count and write it on your log before you start. Applying too little grease starves the bearing; applying too much causes churning, heat buildup, and seal damage — over-greasing is one of the most common field mistakes.

Procedure. Wipe the grease fitting (zerk) clean with a rag before attaching the gun coupler — dirt forced in with the grease defeats the purpose. Apply strokes slowly and steadily, counting aloud. Stay within ±2 strokes of your calculated target. After applying fresh grease, leave the relief fitting open and run the bearing at low speed (if safe) or manually rotate it to allow excess old grease to purge. Collect purged grease on a pad.

Inspecting purged grease under the loupe. Examine the purged grease at 10× magnification. Healthy grease is smooth and uniform in color. Look for: water contamination (grayish, foamy, or emulsified appearance); metal particles (bright or dark flecks — indicate internal wear); color darkening (oxidation or heat degradation); grit or dirt (indicates seal failure). Document every finding on your condition report.

Activity 2 — Gearbox Oil Bath Service

Draining and sampling. Place absorbent pads under the gearbox. Remove the drain plug slowly, allowing oil to flow into a collection pan. Fill a clear sample vial and set it aside for inspection. Observe the oil: black or very dark color suggests oxidation or soot; milky or hazy appearance indicates water ingress (emulsification); metallic shimmer or sludge at the bottom indicates wear debris.

Flushing. Add a small quantity of fresh ISO VG 68 oil, rotate the unit briefly to loosen residue, then drain fully. ISO VG 68 is a common industrial gear oil viscosity grade suited to the operating temperature range of most light training gearboxes; always verify the equipment's nameplate or OEM specification before selecting viscosity in the field.

Refilling and level check. Reinstall the drain plug (hand-tight, then snug with a wrench — do not overtorque). Add fresh ISO VG 68 oil through the fill port until the level reaches the center of the sight glass. The center mark represents the correct operating level; oil below the lower mark starves gears and bearings, while oil above the upper mark causes churning, foam, and elevated temperature. Record oil type, quantity added, date, and your name on the maintenance log form.

Activity 3 — Contamination Scenario

Identifying contaminant type. The instructor pre-contaminates a housing with water and dirt ingress. Disassemble the housing carefully, saving all components on a clean pad. Use your loupe to inspect the bearing race surfaces, rolling elements, and cage. Water contamination causes corrosion pitting on races; abrasive dirt causes dull, scratched surfaces on rolling elements. Documenting the contaminant type directs the corrective action.

Selecting the correct seal. The environment determines seal type:

Select the seal appropriate to the contamination scenario presented, justify your choice on the condition report, and document the bearing replacement recommendation with supporting observations.

Completing Your Documentation

Accurate maintenance records are a professional obligation — they create the history that drives predictive maintenance decisions. Every entry must include date, equipment ID, lubricant type and quantity, findings, and technician name. Incomplete logs are a common audit failure and a safety gap.

Key terms9

NLGI GradeNational Lubricating Grease Institute consistency rating; NLGI 2 is the most common grade for general bearing applications, with a firm, smooth texture similar to peanut butter.
ISO VG (Viscosity Grade)International Standards Organization viscosity classification for lubricating oils; the number (e.g., 68) represents the nominal kinematic viscosity in centistokes at 40 °C.
PurgingThe process of forcing fresh grease through a bearing housing until old, degraded grease exits the relief fitting, carrying contaminants out of the lubrication zone.
Relief FittingA valve or plug on a bearing housing that opens to allow displaced old grease to escape during re-greasing, preventing over-pressurization and seal damage.
EmulsificationThe mixing of water into oil or grease to form a milky, hazy mixture; it reduces lubricant film strength and greatly accelerates corrosion and wear.
Contact Lip SealA shaft seal with a flexible elastomeric lip that rides directly on the rotating shaft to exclude contaminants; effective at low-to-moderate speeds but generates friction heat and wears over time.
Labyrinth SealA non-contact seal that uses a series of close-fitting channels and grooves to create a tortuous path that resists contaminant ingress without touching the shaft, making it suitable for high-speed or wash-down applications.
Sight GlassA transparent window on a gearbox or reservoir that allows visual confirmation of the lubricant level; correct level is typically at the center mark.
Lockout/Tagout (LOTO)A safety procedure (governed by OSHA standards) requiring isolation and de-energization of equipment — plus physical locks and warning tags — before any maintenance activity begins.

Worked examples3

1. A pillow-block bearing has a bore diameter of 40 mm. Using the standard grease quantity formula G = 0.005 × D × B, where D is bore diameter in mm and B is bearing width in mm (bearing width = 18 mm), calculate the required grease mass in grams. Your grease gun delivers 1.25 g per stroke. How many strokes are needed?
  1. Step 1 — Apply the formula: G = 0.005 × D × B = 0.005 × 40 × 18.
  2. Step 2 — Multiply: 0.005 × 40 = 0.2; then 0.2 × 18 = 3.6 g required.
  3. Step 3 — Divide required mass by output per stroke: 3.6 g ÷ 1.25 g/stroke = 2.88 strokes.
  4. Step 4 — Round to the nearest whole stroke: 3 strokes. The acceptable range is ±2 strokes, so 1–5 strokes would be within tolerance, but aim for exactly 3.
Answer: 3 strokes (delivering approximately 3.75 g, which is within a practical tolerance of the 3.6 g target).
2. After draining a training gearbox, you collect a used oil sample. The oil appears milky-white and hazy when held up to the light. You then refill with ISO VG 68 oil. The sight glass has three marks: LOW at 50 mm, CENTER at 75 mm, and HIGH at 100 mm (measured from the bottom of the glass). You add oil until the meniscus sits at 76 mm. Is the level acceptable?
  1. Step 1 — Identify the correct target: center of the sight glass = 75 mm.
  2. Step 2 — Determine the measured level: 76 mm.
  3. Step 3 — Calculate deviation: 76 mm − 75 mm = 1 mm above center.
  4. Step 4 — Compare to acceptance criterion: the check requires oil level at center ±1 mm, so the acceptable range is 74 mm to 76 mm.
  5. Step 5 — 76 mm falls exactly at the upper edge of the ±1 mm band — it is acceptable but at the limit; no adjustment needed.
Answer: The level is acceptable (76 mm is within the ±1 mm tolerance of the 75 mm center mark). The milky appearance noted in the used oil indicates water contamination (emulsification) — document this finding on the maintenance log.
3. You are greasing three identical pillow-block bearings. Each requires 4 strokes. Your grease gun has a known output of 1.0 g per stroke. After finishing all three bearings, how many total grams of grease were applied, and what is the total acceptable stroke range across all three bearings combined (using the ±2 strokes per bearing rule)?
  1. Step 1 — Calculate strokes per bearing: 4 strokes × 3 bearings = 12 total strokes.
  2. Step 2 — Calculate total grease applied: 12 strokes × 1.0 g/stroke = 12 g total.
  3. Step 3 — Determine allowable range per bearing: 4 ± 2 strokes = 2 to 6 strokes per bearing.
  4. Step 4 — Determine allowable range for all three: minimum = 2 × 3 = 6 strokes; maximum = 6 × 3 = 18 strokes.
  5. Step 5 — State the answer clearly.
Answer: 12 g of grease total; the acceptable combined stroke range is 6 to 18 strokes across the three bearings.

The math in this lesson2

Learners convert grease gun strokes at 1.0 g per stroke into grams used across three bearings.
6.RP.3A-SSE.1
Brush up in the math halls at newSchoolWorks.com:
In class: Manual greasing station: students apply the calculated grease quantity (from Lesson 4) to three pillow-block bearings using a manual grease gun, counting strokes, then purge old grease from the relief fitting while checking for contamination (water, metal particles, color change) under a 10× loupe. · Oil bath service: students drain a small training gearbox, collect a sample of used oil in a clear vial for visual inspection, flush with a small quantity of fresh oil, refill to the correct sight-glass level with ISO VG 68 oil, and record the service in a maintenance log form. · Contamination scenario exercise: instructor introduces a deliberately contaminated bearing housing (water, dirt ingress); students disassemble, identify contaminant type, select the correct replacement seal type (contact lip seal vs. labyrinth) for the environment, and document findings on a condition report.
Materials: Pillow-block bearing assemblies; manual grease gun; NLGI 2 grease; training gearbox with drain plug and sight glass; ISO VG 68 oil; used oil sample vials; 10× loupe; replacement seals (lip and labyrinth); maintenance log forms; condition report forms; nitrile gloves; spill absorbent pads.
Check: Instructor observes each student's grease quantity accuracy (strokes within ±2 of calculated value), oil level at center of sight glass ±1 mm, and completed contamination report with correct seal selection — all three tasks must be satisfactory to pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Preventive Maintenance and Lubrication
1. Before attaching a grease gun coupler to a zerk fitting, a technician should first:
Quality, Maintenance, and Continuous Improvement
2. A technician inspects purged grease under a 10× loupe and observes a gray, foamy texture. This observation most likely indicates:
Preventive Maintenance and Lubrication
3. When refilling a gearbox after an oil change, the correct oil level on the sight glass is:
Manufacturing Processes and Production
4. A bearing housing in a high-speed conveyor application is being resealed after contamination is found. The environment has no water washdown but the shaft speed is very high. Which seal type is most appropriate?
Safety and Health
5. What is the FIRST action a technician must take before opening a gearbox drain plug on operating equipment?
Quality, Maintenance, and Continuous Improvement
6. A used oil sample drawn from a gearbox appears dark black with a metallic shimmer and sludge visible at the bottom of the vial. These findings most likely indicate:
Preventive Maintenance and Lubrication
7. A technician calculates that a bearing requires 3.2 g of grease. The grease gun delivers 1.0 g per stroke. After applying 3 strokes (3.0 g), the technician considers stopping. The lab check requires accuracy within ±2 strokes of the calculated stroke count. The calculated stroke count rounded to the nearest whole number is 3. Is stopping at 3 strokes acceptable, and why?
Quality, Maintenance, and Continuous Improvement
8. Why is accurate documentation on a maintenance log form considered a professional and safety obligation in industrial maintenance?
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