Usually they won't wear out - takes some human intervention like a handful of lean runs or a spoon full of dirt in the carb
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My oldest SJ-46 runs very well. Its probably about 200-300 rpm down from when it was a year old....... but it has run just like that ever since no better, no worse. So I consider that "normal"
The very early crankcases were all drilled with the ST X-40/nelson/jett racing mounting holes. All of the jett cases were the same for a while. Evenutally Dub changed the sport engines to match the OS mounting standards.