I have bought a KMC Z8S chain , but it slides over the rear cassette . The model of the cassette is Shimano CS-HG30-81 , it is not worn yet , and the chain length is also perfectly calculated . The problem is in IG / HG compatibility in my opinion , because the chain is a little bit wide , and it has a little play along the teeth of the cassette. Do you have any information about the compatibility of this chain with Shimano HG cassette ?
IG parts are relatively hard to find to begin with, so I'd bet that something is not adjusted properly (or its in your head and you should just deal with it - there is a bit of play when you've gone through a chain or two on a cassette when you put on a new chain at first).
To quote Sheldon Brown:
"Some Shimano 7- and 8-speed cassettes carried the Hyperglide principle even farther, by adding ramps and contouring to both sides of the sprockets. To do this while maintaining the full thickness of the teeth, the designers had to make the sprockets thicker. Since the sprockets are thicker, the spacers must be thinner to maintain the correct spacing. Also, since the sprockets are thicker, Shimano says you shouldn't use H.G. chains on I.G. cassettes. SRAM chains are compatible with both types. Shimano says that you shouldn't mix I.G. and non-I.G. sprockets, but if you use one I.G. spacer per I.G. sprocket, you should be all right. Some experimentation may be required for best results with a mixed setup."
To quote this thread: "All current HG cassette cogs are specially profiled to be HG or IG chain compatible. Any Shimano IG chain will work with any HG cassette. If you use a HG chain with a 7-speed IG cassette (CS-IG50 and CS-IG60) the rear derailleur adjustment becomes more critical. One significant compatibility issue is always to avoid using a HG chain with an IG-only crank set. Why? The chain will release from the large (outer) chain rings too easily while in the larger rear cog. It may be possible that the chain drops off the outer ring without shifting the lever, when under full power."