If you really think you have a knock, take the primary off, take out the spark plugs and spin the motor over by hand and see if you can feel the knock. "Push" the piston one way with the crank to "load" it, and then see if you can somewhat lightly go backwards and listen/feel for it.
Here is a similar test
https://www.youtube.com/watch?v=pYleKxjl0uY