Here is a little more info
Most everyone know these things, as it is very old news
https://www.msn.com/en-us/autos/motorcycles/common-problems-with-the-harley-davidson-twin-cam-engine-and-which-years-to-avoid/ar-BB1p7CQP
Then there's the crankshaft. Again, it's not quite as common as the twin cam's two biggest issues, but there have been instances of crankshaft runout. It's basically when the camshaft -- possibly from manufacturing, maybe due to wear and tear -- goes off-center. Even a few thousandths of a millimeter of distortion can cause excessive vibrations or wear down the engine a lot faster than normal, as well as making lots of noise, though seemingly this particular problem happened more often in modified (stage two and three) twin cams.
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Twin Cam engines also used plastic chain tensioners, which is essential when it comes to keeping enough tension in the timing chain (for synchronizing crankshaft and camshaft rotations). As you might expect, plastic doesn't hold up as well over time as metal. This often resulted in the chain tensioners wearing down rapidly, with plastic shavings from said wear usually making their way into other vital areas. Like the oil pump, which would then lead to engine failure because lots of essential parts weren't being lubricated properly.