Motorcycle Repair: Sudden lost of engine power, metal shavings, carbon buildup

Question
Hi,
I have a question about a 1984 CB650SC. When I bought the bike it had been sitting for 4 years. I cleaned the carbs, replaced the plugs and air filter and changed the oil. Started it and it worked great. I rode it for four hours or so and I started to hear a loud pinging like something was slapping around inside the engine. Then suddenly the noise got much louder and more severe. I immediately started loosing power and then the engine died. It would start again but the noise was still there especially above 2000rpm. I shut the bike down to prevent any further damage and went to work. I took the cams off and checked them visually, they were ok except one journal had some pretty bad scoring. Next I removed the cylinder head and block and they looked ok as well. There was some decent carbon buildup at top rim of the cylinders and the heads and the rings all looked ok. I dont know where to proceed from here and any advice would be much appreciated. Thanks a bunch!

Answer
Pull the oil filter out and take a look.  I'm guessing you will find fine metal shavings.  If the cam bearing are scored it didn't get the oil it needed and you may have rod or main bearing damage.  Was the noise like a rattling noise or a tapping type sound? The sound you described sounded like something dropped into the cylinder but you would have seen that damage when you pulled the head.  There are a number of things that could cause a noise but loosing power and dying says there's a lot of friction somewhere.

Regards,
Rich