an engine knock could be a bad spark plug wire...
on the m103 six cylinder it will run on 5 cylinders
or it could be an internal engine problem probably in the bottom half
like a piston bearing.... or smothing in the bottom of the engine...
(now at this point I am out of my league)
I would think that if it was a piston or lower bearing if you got lucky and it was the front of the engine and you could remove the oil pan i would think it might be possible to disconnect the piston from the crank and replace the bearing.... but i am only guessing... but i am the type of guy to try it...