Rattling noise coming from the engine of my 1993 kawaski zxr 400

It could be three (common) things.

1. Worn/stretched chain.
Test: Measure the 20-link length of the chain under pressure. It should be less than 323mm.
Solution: replace chain (108 link o ring or x ring) and sprockets if required.

2. Incorrect chain tension.
Test: there should be about 25-35mm of slack in the chain.
Solution: Adjust chain tension (make sure you get the rear wheel straight)

3. Worn front sprocket and/or retaining ring.
Test: remove the sprocket cover and chain. Wiggle the sprocket, there should be no (or very, very little) free play.
Solution: Replace the front sprocket.

Note: It could be any or all of these in combination. If you are not completely confident about what you are doing get and expert to check / complete the work. I've broken a chain on my ZXR (due to lack of maintenance), locked the back wheel up and survived. One of my mates had the same thing happen and died, so be safe.

Check to see if the chain isn't stretched. you shouldn't be able to pull the chain off the rear sprocket and see daylight between them....a worn chain is always adjusted for the tightest section and when you do that... the rest of the chain gets a lot of slop in it and it might be hitting the frame of the bike. if its not the chain and or you've installed a new one already...then i would think you should inspect or change out the cam change Tensioner.

Usually kawazaki zxr 400 has these problem the main reason is due to the overspeed.only authorised kawazaki dealer can solve it.....