Wherever an EWP boom bends, a pin and bush make the joint. These pivot points are the hinges that let a boom articulate and telescope, and each one is a critical component carrying real load through a small bearing surface. When a pin and its bush wear, the joint develops play, and play at the base of a boom is magnified into alarming movement out at the platform. This guide covers how pins and bushes wear, the symptoms that reveal it, the way inspectors measure the play and how a worn joint is properly restored.
Symptoms of worn pins and bushes
Wear at a pivot point shows up as movement, noise and marks:
- Play or slop at a boom joint — the boom can be felt or seen to move at the pin before the structure itself takes up the load.
- Knocking or clunking as the boom changes direction, when the pin rattles in an oversized bush.
- Excessive, magnified movement at the platform end, because a small amount of play low on the boom translates into large movement at reach.
- Elongated or ovalled pin holes, scoring on the pin, or a bush that has spun or extruded from its bore.
- Dry, squealing joints or grease that has stopped taking, which usually precede accelerated wear.
What causes pins and bushes to wear
- Missed or inadequate lubrication, which is the single most common cause — a dry pin and bush wear each other away quickly.
- Grit and water working into the joint past worn seals, grinding the bearing surfaces.
- High cyclic loading at heavily worked joints, especially the lower boom pivots that carry the most moment.
- Retaining hardware that has loosened, letting the pin migrate and wear unevenly.
- Corrosion on the pin surface, which then abrades the bush.
How inspectors measure the play
Pin and bush wear is assessed by measuring the movement at the joint. An inspector will articulate the boom to load and unload the pin and gauge the resulting play, often with a dial indicator, comparing it to the manufacturer's allowable tolerance. Where a pin can be withdrawn, it is measured for diameter and inspected for scoring and cracking, and the bush is measured for bore wear.
Because pins and bushes are critical components, they get attention at periodic inspections and are examined thoroughly during the major inspection, whose AS 2550.10 interval is 5 years for one group of machine classes and 10 years for another, when the unit is disassembled far enough to withdraw and gauge them directly.
How a worn joint is restored
A worn pivot is not fixed by adding grease and hoping. If the pin, bush or the hole they run in has worn beyond tolerance, the components are renewed so the joint runs on fresh bearing surfaces.
- Support the boom safely and withdraw the pin so the joint can be assessed properly.
- Renew the pin and bush with the correct components, and where the parent bore has ovalled, restore it — for example by machining and fitting an oversize bush or re-bushing — as an engineered repair.
- Refit new retaining hardware and confirm the pin is correctly located and secured.
- Lubricate the joint and verify the grease path is clear so the new components are protected from day one.
- Function test the boom, re-check for play and record the work in the logbook.
Preventing premature wear
Lubrication is everything. Greasing every pivot on the manufacturer's schedule, and confirming the grease is actually reaching the bearing surface rather than blowing past a blocked path, is the cheapest and most effective way to make pins and bushes last.
Keeping seals intact to exclude grit and water, and dealing with any developing play promptly, stops a minor wear issue becoming an ovalled hole that needs an engineered repair. Play felt at a boom joint should be reported and assessed, not worked around.
This guide is general information prepared by EWP Australia and is grounded in publicly available Australian Standards and Safe Work Australia material. It is not a substitute for the current published edition of the relevant standard or for site-specific engineering advice. Always work from the current standard and consult a competent person for your specific equipment and application.