Originally Posted by Toobuilder
I don't mean to imply that a new crank is "unsafe" - my main question really is: "What does the extra $4k buy me?" In my brain I can't come up with anything, and it seems this forum supports that.
Concerning the overspeed, it was in excess of 3800.
Assuming the factory cranks are made on modern machinery and managed with current best practices quality control (air gauges, SPC, etc).
I would say a high probability exists for a better dimensional consistency and surface finish of bearings and proper nitride hardness/depth (along with a 100 more details). Basically a more precision piece. This makes for (typically) more reliable part.
But as long as the "rebuilt" crank had only ground surfaces, and re-nitrided with good inspection procures on each crank, then it would be just as good for its original purpose. And both sourced parts are still bound by the same TBO requirements.
You might want a mag and eddy current inspection just to be sure for sub surface inclusions that might have grown in service. They are not detected by mag inspection.
I think it kinda is how much money you want to spend for a little better "insurance".