Track Pinion and Gearbox Maintenance — Wear, Dropped Pinion, Oil-Like Stains¶

CONFIRMED MECHANICAL SERVICE CHECK

Summary¶

The track pinion is intentionally more sacrificial than the rack. Community guidance says the pinion should wear before the harder rack and is cheaper/easier to replace. Later reports cover pinion drop, rack-clamp contact, gearbox oil-like stains, and noisy axes that require service-level inspection.

Symptoms¶

Metal dust around track pinion
Vibration or unsatisfactory tracking results
Pinion dropped a few mm and contacts rack clamps
Oil-like stains around axis/motor/gearbox
New noise from an axis that changes with load/position

Stable ID¶

ISSUE-MAINT-001

First Reported¶

2020-10-07 — track/pinion wear and rack replacement question.

Additional Reports¶

2021-07-15 — warning against running questionable rack/pinion engagement.
2025-07-09 — oil-like stains and noisy Bolt Jr+ axis/motor.
2025-08-06 — Bolt Jr pinion dropped and hit rack clamps.
2025-09-19 — oil source from bearing seal or filling ports.

Hardware¶

Bolt / Bolt Jr+
Precision Track rack and pinion
Track gearbox
Turntable / gearboxes as related mechanical reference

Possible Causes¶

Normal sacrificial pinion wear
Heat/sun expansion and heavy track use
Pinion retaining nut loosening
Backlash adjustment required
Bearing seal / fill port / gearbox oil issue
Load offset or bearing problem

Community Solutions¶

[CONFIRMED] 2020-10-07 — User: Simon Wakley¶

The robot pinion is sacrificial and should wear before the harder rack. The rack should generally not need replacement; the pinion is easier and cheaper to replace.

confidence_score: 0.86

[CONFIRMED] 2021-07-15 — User: Gordon Eschke¶

Do not run on a questionable/damaged track setup. It can damage the pinion and produce vibration or poor results.

confidence_score: 0.82

[LIKELY] 2025-07-09 — Users: Jeremy Andrews, Stafford¶

Oil-like stains and noise need inspection. Identify whether oil comes from bearing seal or filling ports. Gears sit in an oil bath with drain and filling ports. Noise may indicate bearings/load offset or pinion backlash adjustment.

confidence_score: 0.68

[CONFIRMED] 2025-08-06 — User: Simon Wakley¶

If the pinion has dropped and is hitting rack clamps, check pinion tightness. The bottom of the pinion should be roughly level with the bottom of the track teeth. A special four-notch spanner and Loctite/spec may be required; consult MRMC for exact service details.

confidence_score: 0.82

WhatsApp Excerpts¶

2020-10-07 00:09 - Timothy Heys Cerchio: Yes, heat and sun have often caused this issue. Especially with Rack + Pinion movement for Track. Rack and Rails dilate differently with changing temperatures.
2020-10-07 04:23 - ~ Peter Constan-Tatos: Simon is it not worth getting the rack made in AL? I’m sure it will still be strong enough if it’s an aerospace grade 6061.
2020-10-07 04:36 - ~ Simon Wakley: That’s an MRMC question but possibly if it were thicker it would be just as strong. Obviously it’s a custom racking but we used to use off the shelf pieces. The idea is that the robot pinion is sacrificial and wears out and is easy to replace and relatively cheap. The racking is deliberately much harder and so should NOT need to be replaced
2020-10-07 04:58 - ~ Peter Constan-Tatos: Agreed Simon. The rack is really expensive to cut.
2020-10-07 05:04 - Timothy Heys Cerchio: Plus, as a further thought, if the Rack has lower linear expansion as it is, would it not be more in favour of repeatability?
2020-10-07 05:12 - ~ Simon Wakley: 30 metres of steel changed by 30c would move 11mm on the track, assume the middle is still that’s 5mm at the end of the track. It’s something you have to live with in location