Timing belt to Timing chain?
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Timing chains still need to be replaced too. It is just that they are less likely to break. They will just usually stretch out and jump timing instead of breaking; however, they can do that as well. It's a once per 100,000 mile job. It's not like that occurs often enough to make it a major PITA. The cost of trying to convert it will probably far outweigh just changing the belt.