They go as early as 16k cause the chain wears fast and the tensioner only has so much expansion before it literally disassembles itself inside your case. I have a modified one to prevent that but at 45k miles the chain is nearly out of stretch.
Theres also an issue with an oil leak caused by a plug in the head. When you can get the head cover off the engine, make sure you have a newer model of the plug (old one looks like a cup, new one like a puck) and seal that bitch up with gasket material (why they don't do this from the factory is beyond anyone)
Hit me up if you ever want to do a bare-bones wiring loom. I'm not too smart on where I place my wires (had 3 small short-induced fires to date), but I have the CDI box figured and removed the decompression system, signals, and safety circuit and with no issues for 2 years.
Here's mine... top end is in the shop to check for wear and deglazing