Rotary Drive: The High-Cost Center of a Used Rig
On a used rotary drilling rig, the rotary drive is a core system that turns hydraulic power into torque. A video of the head spinning freely does not show whether the gearbox has worn bearings, the brake holds load, or the drive keys are tight. That clip is a starting point, not an inspection.
The rotary drive inspection must move from cold condition through a controlled warm test, using visual baselines and post-run evidence. Its purpose is to assign a risk level to a high-cost component, not to confirm that it spins.
Build a Stock-Specific Identity Sheet
Before any price discussion, note the exact rotary drive configuration. Look for the gearbox nameplate, motor numbers, brake type, key bar arrangement, and lubrication points. Comparing these with the original manual reveals if parts were swapped or if the drive differs from the standard build.
Record repair or rebuild claims against an exact stock ID. If the seller says the rotary head was rebuilt, demand an invoice or work scope. Fresh paint, clean oil, and a shiny case are cosmetic.
Cold Visual and Leak Baseline
Start before the machine runs. Walk around the rotary drive and look for oil trails, pooled fluid, wetted hoses, and residue at seals. A leak that appears only under pressure is different from a static dribble. Check the oil on the dipstick or sight glass, noting color and smell to detect fresh oil.
Inspect the drive key bars and their contact with the Kelly bar. Wear here generates shock loads. Look for loose bolts, cracked welds on the case, and recently removed inspection covers. This baseline gives you a comparison for the post-test condition.
