A roller chain that skipped teeth after 6 months. The drive was a 08B chain, 16-tooth driving sprocket, 48-tooth driven, center distance 600 mm. The conveyor ran 24/7. The customer re-tensioned the chain. It skipped again after a month. The chain wasn’t worn out — but the sprockets were. The worn sprocket teeth allowed the chain to ride up and skip. This is about chain drive maintenance and wear elongation.
Chain wear elongation
A roller chain wears as the pins and bushings corrode and abrade. The chain gets longer (elongates). At 1.5% elongation, the chain should be replaced. For a 1-meter span: 1.5% = 15 mm. The chain rider on the sprocket teeth moves outward as the chain elongates. At 2% elongation, the chain rides on the tips of the teeth and skips.
The failed chain had 2.5% elongation (25 mm on a 1 m span). The customer measured the chain length with a tape. He thought it was fine because it still looked the same. But the sprockets were also worn — the tooth profile had hooked over from 6 months of operation. Even a new chain would skip on the hooked teeth.
What I changed
1. Replaced both chain and sprockets. You never replace a chain without replacing the sprockets (or at least the small one). A new chain on worn sprockets wears 5x faster. I replaced the 16-tooth driver (the small sprocket wears faster due to more tooth engagements per meter). The 48-tooth driven was still okay but I replaced it anyway for reliability.
2. Increased the center distance adjustment range. The original tensioner only allowed 20 mm of adjustment. At 2.5% elongation, the chain needed 25 mm. I redesigned the tensioner slot to allow 40 mm. The chain can be re-tensioned until it reaches the replacement threshold (1.5% = 15 mm… wait, that’s less than 40 mm). Actually, the elongation at replacement is 1.5% of the chain length. For a 2 m chain (both strands), that’s 30 mm. The 40 mm adjustment covers the full wear life.
3. Added oiler. The chain ran dry. I installed a drip oiler that feeds 1 drop per minute of chain oil. The chain wear rate dropped by 70%. The chain now lasts 3 years instead of 6 months. The oiler costs $30. The chain and sprockets cost $200.
The minimum sprocket teeth
The number of teeth on the small sprocket affects chain life. Too few teeth (under 12) and each tooth takes a heavy load. Too many (over 120) and the chain jumps at tiny wear. The sweet spot is 17-25 teeth for continuous drives. The 16-tooth driver was fine — but at 24/7 operation, I’d spec 19 teeth for longer life. The 19-tooth sprocket costs the same but reduces the tooth load by 15%.
Chain vs belt for conveyors
| Factor | Roller chain | Timing belt | V-belt |
|---|---|---|---|
| Efficiency | 98% | 97% | 95% |
| Wear life (24/7) | 2-3 years | 5-7 years | 1-2 years |
| Maintenance | Lubrication + tension | Tension only | Tension only |
| Backlash | None (positive drive) | None | Slips under shock |
| Cost | Medium | High | Low |
The chain I replace: always with sprockets, never alone. The skipping chain wasn’t defective — it was worn to 2.5% elongation on hooked sprocket teeth. Add an oiler, use 19+ teeth on the driver, and measure elongation every 6 months. Replace at 1.5%.
