Well assuming the reason is due to a rattling in the engine at idle??
It's a job that will take a reasonable degree of mechanical knowledge..since usually the tensioner is worn out at about the same time the timing chain is all stretched and ready for replacement. Since it means pulling the motor from the machine(some say it can be done in) and the head/cylinder removed you are basically talking about a full top end job.
If it doesn't smoke too bad and the cylinder & piston aren't scored you could likely get away with a new set of rings/gaskets/chain&tensioners. Then hone the cylinder and put it all back together..a pretty good job to cut your teeth on actually.
Just be prepared for some breakage and complications as you take things apart..exhaust studs and such.
Current toys..
1986 Honda 350X..trail bomb!
1985 Honda 250SX..my main mudder
1985 Honda 250ES..Back in Black Trike
Current non-trike toys:
1990 Honda TRX300FW
1995 Seadoo GTX
1998 Polaris Indy Lite 340(Nearly new looking)
1998 Polaris Touring 500
1998 Club Car (electric)