How much oil does it have in it?
It has some oil, but running low. The tip of the dipstick is wet.
:nono:
Low oil can cause several problems. Tight valves and crank bearing failure are two of the first things that come to mind. Loss of power would indicate valve problems. But the knocking sounds like bearing failure. Then there is always burnt rings that would have both symptoms. Check the valves first since it is the least involved.