Iv just bought a 4x4 saff and looking for a little bit of adivse.

I took the cambelt cover off today and when you press down on the top of the cambelt it goes up and down quite abit as if its not that tight, im assuming it should be quite tight? And when the engine is running you can see it going up and down, is this correct or not as i think? If you understand how iv expplained it!

Hope someone can help, thanks