Bowling balls don't have expiry dates. But their lifespan is determined by the condition of the cover, mostly. I've only known of people who retire balls when they crack or have the coverstock lose it's bite. (Ian's DZ plays like plastic) Afterall, one can't tell if the core spoils. :p
Moral of the story: Maintain your equipment.
On this note, though... I heard that the Quantum Raven (1997) was a pure tournament ball and was made to last only a while. Something about it's core changing shape and ''dying'... It cost S$500 at the time, some S$100 more than the next most expensive ball, so I'd assumed that it was true. Anyone heard this too?
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Always remember: It's easier to spare from a channelball than a split.