I would do a compression test first. (Throttle wide open) A knock could be from a worn piston, worn piston pin bearing, or hopefully not...a bad connecting rod lower bearing. You might be able to remove the exhaust pipe and look into the cylinder to see if the piston looks "scratched." This is a sign of dirt, or overheated.
Answers & Comments
I would do a compression test first. (Throttle wide open)
A knock could be from a worn piston, worn piston pin bearing, or hopefully not...a bad connecting rod lower bearing.
You might be able to remove the exhaust pipe and look into the cylinder to see if the piston looks "scratched." This is a sign of dirt, or overheated.