Timing chain questions

[bean-oil]

So, I might be trading my trusty 2 smoker 06 rm250 for a 04 yfz450. The guy says the bike needs a timing chain and it wont start until a new one is installed because it wont stay timed. How hard is it to replace the timing chain? Im new to these 4 strokes but if I had a clymer manual in hand I think I could get the job done.

[ldjbuff]

I would have it checked out by a dealer before making the swap, could be a lot more things wrong with it