I have a 1985 big red 250, runs perfectly at the moment, bought it off my uncle. He and I have both been driving it quite a lot for the past 7 or 8 years he's owned it, the timing chain has never been done. It's not noisy or anything, I just want to get it done as preventative maintenance. When I buy the parts, what am I to buy? Just the chain and the 2 gears? Do I need a gasket kit? Do I need to replace the tensioner? Any advice would be appreciated, thanks.