[Jack Shaft]

There are alot of folks around who do engine work. a cheap harbor freight stethoscope can help to pinpoint the knock.Years ago mechanics would do an 'overhaul' ..hone cylinders,fit new piston rings,lap valves, adjust rod and main bearings to restore power.Cant tell whats wrong with your engine over the interwebs..whole lot of guesses and assumptions will come forth,guaranteed.