My Z400 had such a loose cam chain that the valve-train noise was nearly as loud as the stock exhaust. My buddy heard it and said not to even ride it again until I replaced the cam chain, for fear of skipping a tooth on the cam sprockets and smashing a valve into the piston. I ordered this cam chain, a clutch cover gasket, and a gasket for the automatic chain tensioner (wasn't needed, but good to have anyway). Get a new spark plug too while you have the gas tank off. I found a good write-up at suzukicentral on how to replace it, and tackled the job in about 4 hours. Really wasn't too bad a job. My automatic chain tensioner was fully extended when I removed it from the engine, meaning I was riding on borrowed time. Now its quiet as ever with this new chain in it, and feels much more responsive and 'crisp' to ride and shift. If you looking at replacing your cam chain get a good one like this, and you'll be set for quite a long time.