So I have a 199X Vulcan 750. My uncle gave it to me and said it has a knocking in the engine. He said he’s not sure what’s causing it. It had been drained of the oil but my dad and I put oil in it and charged the battery and it cranked right up. We didn’t hear any knocking or anything but my uncle said if we let it sit and run for a few minutes we’ll start hearing it? Does anybody know what it might actually be and possibly how I would go about fixing it? Thanks

the camshaft chains are a common problem.. sounds more like a rattle/slap than a knock tho.

listen for it to happen, and get a recording of it if possible.

if it is the chains, the solution is pretty simple and cheap

I refurbed an 85 with 50,000 miles on it. Once I got rid of the cam chain noise by installing manual adjusters, I was left with a very audible knock. The engine has a balancer weight on the crankshaft which is attached using rubber bushings. These rubber bushings can deteriorate over time. When they do, they allow the counterweight to contact the crank, metal on metal, which makes the audible knock. They are called balance dampers. The replacements are cheap. Changing them requires pulling the engine out of the frame. Wasn't too bad of a job. Got me familiar with the bike.