TL;DR

Rising vibration and bearing temperature on a top drive main shaft indicate bearing wear. Log baseline readings and plan a bearing inspection at the next stand connection opportunity.

What you might see

vibration increasing at the top drive housing
main shaft bearing temperature rising
abnormal noise during rotation
motor torque requirement increasing

Likely causes

Tap to mark as ruled out

Lubrication failure from low oil level or degraded gear oil
Overload from drilling with weight on bit above the drive rating
Bearing fatigue after extended rotating hours
Shock loading from stuck pipe releases or jarring operations

Required tools

Vibration meter
IR thermometer
Gearbox oil sample kit
LOTO kit

Safety first

Top drive work on the rig floor requires fall protection and a tool inventory check. All tools must be tethered when working above the rig floor level.
The top drive handles drill string loads of hundreds of tonnes. Do not work under a suspended top drive without appropriate suspended load controls.
Lock out the top drive rotation and the drawworks before accessing the top drive for any inspection or maintenance.

Procedure

7 steps · ~45 min

1
Record the main shaft bearing temperature from the top drive monitoring system at the current operating condition.[1]
2
Connect a vibration measurement device to the top drive housing. Record velocity at the bearing housing.[1]
3
Check the top drive gearbox oil level at the sight glass. Low oil is the most common cause of early bearing failure.
4
Review the weight on bit and torque history. Sustained operation above the rated values increases bearing load.
5
Take a gearbox oil sample for analysis. Metal particles confirm active bearing wear.
6
If bearing temperature exceeds the alarm setpoint or vibration is above the acceptable limit, reduce rotary speed and plan an offline inspection at the next rig floor opportunity.
7
Bearing replacement on a top drive requires the unit to be laid down or a rig-floor bearing change with a qualified top drive technician.

Sources

NOV (National Oilwell Varco) NOV TDS-11SA / Ideal Drilling Rig / Top Drive general technical documentation, NOV (National Oilwell Varco)
NOV TDS-11SA / Ideal top drive general main shaft bearing inspection and maintenance procedures (general)

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