Over-Greased Motor Bearing Running at 205 F

Most likely cause: gross over-greasing and churning.

• Volume delivered: 40 strokes x 0.03 oz = 1.2 oz (about 34 g) per bearing.
• A relubrication of this bearing should be a few grams at most; a full initial fill of the cavity is in the same range as what was just injected, on top of what was already there.
• With no free space, the balls must push solid grease through the cavity. That churning shears the grease, generates heat, and drives temperature up. The high-frequency broadband vibration with no discrete defect peaks fits a churning/starved-film condition, not yet a spalled race.
• 205 F (96 C) is far above normal for this bearing and puts grease life in real danger: grease life roughly halves for every 27 F (15 C) above the design temperature.

Immediate actions:

1. Remove the drain/relief plug on the over-greased end bell so excess grease can purge, and catch/collect the purge.
2. Run the motor unloaded if the process allows, and monitor temperature closely for 30-60 minutes. A purging bearing will typically peak and then fall.
3. Do not add more grease and do not assume the gun was loaded with the same grease.
4. If the temperature keeps climbing and does not break over, shut the machine down. A seized bearing can destroy the rotor and the end bell.
5. Verify the grease in the gun is compatible with the plant standard before any further lubrication - an incompatible thickener can soften a grease into a fluid and cause exactly this.

Confirm:

• Temperature trend with the plug out: a peak-then-fall curve confirms churning. A flat or rising curve suggests the damage is already done or that something else is wrong.
• High-frequency vibration trend (spike energy or acceleration envelope) taken at the same load and speed points; it should fall as the excess purges.
• Thermography on the end bell compared with the opposite end.
• Verify what was actually installed: grease type, NLGI grade, base oil viscosity, and thickener, against the motor nameplate or manual.

Correct the practice:

1. Get the bearing's specified charge from the motor manual: initial fill by weight, and relubrication quantity in grams or ounces - not "strokes."
2. Mark the gun or use a calibrated one so a stroke equals a known quantity, and record the quantity on the PM route.
3. Set the interval for this duty (speed, size, temperature), not a blanket quarterly. High-speed horizontal machines often need small, frequent doses rather than large ones.
4. Standard procedure: clean the fitting, grease with the machine running and the relief plug out where the design allows, add the specified amount only, and let it purge before reinstalling the plug.
5. Train the technician on why more grease is not better, and add a feedback step: any bearing that feels or sounds dry gets a vibration check, not an automatic extra shot.

Interpretation: the thermal event left damage or a film problem behind.

• The over-grease sheared and possibly oxidized the grease. Degraded base oil means the film is marginal, so the high-frequency band creeps up as surface distress begins.
• A growing 1x radial can come from a developed raceway or ball defect, but also from imbalance, a belt problem, or looseness. Do not attribute 1x to the bearing without checking the belt sheave and the fan, which are the more common sources on a belt-driven train.
• A true bearing defect usually appears as a discrete defect frequency (BPFO/BPFI/BSF) with sidebands, not just a broadband floor. The original complaint had no discrete peaks, so this is a new development.

Actions:

1. Trend, don't react: take readings at the same load, speed, and temperature weekly, and plot the high-frequency trend against a baseline.
2. Take a grease sample or wipe a purge sample and check for discoloration, hardening, and metallic content.
3. Verify belt tension and sheave condition to rule out 1x from the driven side.
4. Check the grease spec against the actual service temperature and confirm the correct product was reinstalled after the purge.
5. Plan a bearing replacement at the next planned outage if the trend continues, and specify the correct charge and a proper break-in, since the next failure mode is a seized bearing and a damaged shaft or end bell.