[viejopatron]

Razor, FWIW Chain tensioner failure and the aforementioned results is a “chain” [Har!] of related events. By design, chain drives have and need some slop for several reasons, so it’s always there.

Failure starts with the catastrophic failure of the tensioner spring. This spring spends most of it’s life stressed to a relatively high level and consequently is designed to use a high-strength, not-real-ductile material. So when it fails, under load, it snaps and that load, used to tension the chain, disappears. Now here’s where the variables come in. A new system, with no or little wear in chain, ramps, bearings, etc. will have minimal slop. In a used system as wear progresses [it always does], slop increases. If you’ve ever observed free slop in a high-speed chain drive, it looks like a “bump” in the chain line and will move back and forth between sprockets as load changes. In the cam chain drive, when that bump travels up to and on a sprocket… Well, let’s just say the rest can be spectacular.

Bottom line: Be aware of wear.