Apart from regular maintenance (oil, filter, valve checks and adjust) at 180,000kms the engine is unopened and original clutch (ST11 1996). ST13 should be better as no timing belt change at 150,000kms. I do oil and filter changes like Brock says, at around the Honda interval or earlier/later depending on trips. I haven't really heard of anyone doing engine work on an ST13 (some water pumps and thermostats aside, but you get that with cars as well)