If you're running 20-50w motor oil with Lucas and it's still knocking - you need to open up the bottom end of that thing. I've been dealing with knocks a long time, and if you keep running it like that until it knocks all the time, you will be stuck pulling the crank and turning it.
I've changed only the rod bearings on a few motors with a slight knock and it fixes it if you don't wait.
I'm just saying. If you fix it early, it's easier.....