The Cylinder That Got Loose After 6 Months
We used a clevis-mounted cylinder (article 121) to push a part. On the bench, it moved squarely. After 6 months, the cylinder got loose — the rod tilted as it extended. The part didn’t push straight. The problem: the pivot bushing (the clevis pin’s bearing) wore. The clevis pin went through a bronze bushing in the cylinder’s clevis. After thousands of cycles (the cylinder pivots as it extends), the bushing wore (the hole enlarged). The pin wobbled. The cylinder tilted. We replaced the bushing (a sintered bronze one). The play went away. The mistake was using a plain (unlubricated) bushing in a high-cycle pivot. For a high-cycle cylinder, use a self-lubricating (or needle) bushing.
Cylinder pivot bushing wear is about the bearing at the clevis. This article covers the selection.
The Pivot (Clevis) Joint
A clevis-mounted cylinder (article 121) pivots as it extends (the rod end swings). The pivot has a pin (through the clevis). The pin goes through a bushing (in the clevis eye). The bushing takes the load (and the rotation). Over cycles, the bushing wears (the hole enlarges, the pin wobbles).
Bushing Types
Plain Bronze (Sintered)
A sintered bronze bushing (oil-impregnated). Cheap. Takes moderate load. But in a high-cycle pivot (the cylinder swings thousands of times), it wears (the oil dries). For low-cycle (a few cycles a day), it’s fine. For high-cycle (1000+ cycles/day), it wears in months.
Self-Lubricating (POM or PTFE-lined)
A plastic (POM) or PTFE-lined bushing. No lubrication needed (it’s self-lubricating). Low friction. Wear-resistant for high-cycle pivots. The standard for automation cylinders. More expensive than sintered bronze, but lasts.
Needle Roller (Rolling Element)
A needle bearing (rolling elements). Very low friction, takes high load. But expensive. For heavy loads (a big cylinder, a high force). For light loads (a small cylinder), overkill.
| Bushing Type | Cycle Rate | Best For |
|---|---|---|
| Sintered bronze | Low (<100 cycles/day) | Light, infrequent use |
| Self-lubricating (POM/PTFE) | High (1000+ cycles/day) | Standard automation cylinder |
| Needle roller | High, heavy load | Big cylinders, high force |
Step 1: Match the Bushing to the Cycle Rate
For a cylinder that cycles 1000×/day (a typical automation axis), use a self-lubricating bushing. The cylinder that got loose had a sintered bronze bushing (wore in 6 months). Switch to POM/PTFE. The play stays low for years.
For a cylinder that cycles 10×/day (a manual station), the sintered bronze is fine (the wear is negligible).
The pivot bushing rule: For high-cycle cylinders (1000+ cycles/day), use a self-lubricating (POM/PTFE) bushing. The cylinder that got loose had a sintered bronze bushing (wore). The self-lubricating bushing doesn’t need oil and lasts. Inspect the play quarterly.
Step 2: Rod End Joint (Heim Joint)
The rod end (the clevis on the rod) also has a joint (a Heim joint or rose joint). It also wears. For high-cycle, use a quality rod end (with a PTFE liner). A cheap rod end (plain bronze) wears fast. For a vertical load (the rod hangs a weight), the rod end takes the load — use a heavy-duty one.
Step 3: Lubrication
A self-lubricating bushing doesn’t need oil. But it benefits from a little grease (every 6 months). A sintered bronze bushing needs periodic oil (it’s impregnated, but the oil dries). If you use sintered bronze, schedule oiling (every 3 months).
Step 4: Check the Play
Inspect the pivot play quarterly. Grab the rod, try to wiggle it side-to-side. If there’s noticeable play (over 0.5 mm), the bushing is worn. Replace it. A worn bushing lets the cylinder tilt (the push isn’t straight). It also wears the seal (the rod tilts, the seal leaks).
A Pivot Bushing Checklist
- How many cycles/day? (High?)
- For high-cycle: self-lubricating bushing?
- Is the rod end (Heim joint) quality? (PTFE liner?)
- Is the cylinder horizontal or vertical? (Load direction?)
- Is the play checked quarterly? (Wiggle the rod?)
- Is the bushing replaced when worn? (Play over 0.5 mm?)
- Is lubrication scheduled? (If sintered bronze?)
- Is the push straight? (No tilt?)
- Is the seal not leaking? (Rod tilting?)
- Are spare bushings in stock? (Article 100?)
The Bottom Line
Cylinder pivot bushing wear — high-cycle pivots need self-lubricating bushings. The cylinder that got loose had a sintered bronze bushing (wore in 6 months). Use POM/PTFE for high-cycle, sintered bronze for low-cycle, needle roller for heavy loads. Check the play quarterly. The cylinder that stayed tight wasn’t the biggest one — it had a self-lubricating pivot.
