Hi guys

So I was given a Honda CB100 that was last taxed in 1996, its circa 1982-1984 manufacture. It would appear to have a genuine 15,000 miles on it. So probably used for a short commute, around 10-15 miles per day by my calculation. Its in surprisingly good condition, obviously stored somewhere dry. I have rebuilt the top end. The cam chain had broken, one of the valves was bent, exhaust I think I recall, piston badly scored. All replaced. I have no spark on it, but ill go through that, could be anything from magneto, condenser or coil, battery obviously completely dry and dead. Maybe thats the reson? Not got that far yet. But my question is this, before I fire it up. What caused the initial damage? What came first I think one of 4., 1. seize, breaking the cam chain and bending the valve. 2. Broken cam chain, bending the valve, I can see this would cause damage to the top of the Piston. But scoring to the skirt of the piston? 3. Valve stuck, breaking cam chain, but again scoring to the piston skirt?. The piston rings were stuck. 4. lack of oil. It looks like oil starvation to me, but the the crank case had sufficient oil, and would appear to be the original oil. Dark, with filings I suspect from the piston stuck in the oil screen so looks like its original oil. Could there be a problem in the oil delivery, how can I check that without repeating the damage? I understand the right hand side of the crank case needs to be removed to check the oil filter. Any ideas?