when does the timing belt/chain needs to be changed?

The problem is that on most vehicles you won't. Check your owner's manual or call the local dealer. Most vehicles that have a timing belt need a replacement at 60k or 90k. If you have an interference engine, you'll ruin it if the belt breaks. Often times it can be over $2,500 to fix the engine. If you have a non-interference engine, it can only break and leave you on the road side. Expect to spend $400-$600 to have it replaced. Also, if the belt drives the water pump, replace it at the same time and save a lot of money. Finally, if you just bought a car and can't verify when it was replaced, be pro-active and replace it on an interference engine car. Your local dealer can tell you if it is an interference engine. Good Luck!