I see all these issues about cam chains and tensioners. But i can't ever figure out what the "complaint" that these issues causes.

so..... What kind of problems does a bad chain or chain tensioner
or guide rails cuase?

thanks

if there's enough wear that the tensioner can no longer take up the slack, the tensioner plunger looses contact with the housing and falls out.  This allows the chain to come loose.  Sooner or later the chain looses contact with the cam sprocket and the cam goes out of time with the crank and piston.  The piston comes up and says howdy to the valves.  The party that ensues is not a pretty one.