Monday Morning Walk-Around: Nine Findings and a Concrete Pour
At 06:40 on a Monday, 8°C, an 11,400-hour 20-tonne excavator is due on a concrete pour at 08:00. The 45-minute walk-around finds: a 150 mm damp streak running down the boom cylinder rod with a drop hanging from the wiper seal; the hydraulic tank sight glass reading just below MIN with the oil cold; coolant at the LOW mark; left track sag of 45 mm against a specification of 10–20 mm; the air filter restriction indicator showing red; a dry, polished bucket-to-linkage pin with no grease at the fitting; a 20 mm crack through the weld on a bucket tooth adapter; and a 200 mm puddle under the left final drive that smells like gear oil rather than hydraulic oil. The supervisor says the pour cannot move and to run it and write everything up at lunchtime.
1. Triage every finding as stop-work, fix before start, or monitor, and explain the reasoning behind each call.
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Stop-work:
- Cracked tooth adapter (20 mm through the weld). The tooth can leave at bucket speed and strike the cab, a person or a truck. Weld repair on a loaded adapter is a specialist job; fit a replacement.
- Gear-oil puddle under the final drive. A failed seal will run the final drive dry and destroy it, and the oil is a slip and environmental hazard. Check the level plug before any travel; travel risks a seized hub and a stranded machine.
Fix before start:
- Air filter indicator red. Restriction costs power and fuel and lets dust past a distorted element. Clean or replace, then reset the indicator.
- Track sag 45 mm (spec 10–20). Loose enough to derail under a side load or a turn, and it hammers the idler and sprocket.
- Dry, polished pin. Polishing means metal-to-metal contact; grease now before the pin and bush are scrapped.
- Coolant low. Top up and find where it went - an external leak or a head gasket symptom.
Monitor and investigate (do not simply top up): the 150 mm damp streak plus the low sight glass. A wiper-seal weep alone may be tolerable, but a low tank on a cold machine points to piston-seal bypass. Record it, test the drift, and plan a seal kit.
2. Describe the track tension adjustment and explain the consequences of both loose and over-tight tracks.
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Adjustment (typical, always confirm against the manufacturer's manual):
- Park on level, hard ground and clean the track and the area around the tensioner.
- Raise the track clear of the ground using the boom and blade, and block the machine securely - never work under a machine held only by hydraulics.
- Measure the sag in the longest free span (between the front idler and the drive sprocket) from the bottom of the shoe to the top of the... i.e., the gap between the track and the roller/ frame per the manual. Spec here is 10–20 mm.
- Add grease through the tensioner nipple to tighten; to loosen, open the relief valve slowly - no more than about one turn - standing to the side, because the grease is under very high pressure.
- Re-measure, lower, and re-check after a few cycles.
Consequences: too loose and the track can climb off the idler or sprocket in a turn or on a side slope, links slap the frame, and the idler and sprocket wear fast. Too tight and shock loads go into the idler bearing, the seals and the final drive, with power loss and heat. Both are avoidable in ten minutes.
3. The low hydraulic oil and the weeping boom cylinder appear together. What does that combination suggest, and what will you actually do before 08:00?
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What it suggests: the boom cylinder's piston seal may be bypassing. Oil moves from the rod end to the head end (or past the piston), so the rod end can pressurise and the wiper seal weeps, while oil is displaced back to the tank and the level reads low when the cylinder is extended. When the boom is fully retracted the level can rise again - which is why simply topping up can hide the fault and why the machine may later 'make oil' in the tank.
Checks before work:
- Raise the boom, stop the engine, and measure drift over 5 minutes against the manufacturer's limit. Drift plus a wet rod means the cylinder is coming off.
- Look for scoring or a bent rod, oil in the rod-end boot, and check the other cylinders and the return filter for debris.
- Clean around the filler cap before opening it; fill cold to the specified level, run the functions through a couple of cycles, and re-check.
Decision: if drift is within limits, work may proceed with the fault logged and a seal kit ordered - but not over people. If drift is excessive or the level falls again, the machine is parked; a boom that creeps is a dropped-load waiting to happen. Report the combination to the supervisor in writing.