Normally from lack of proper lubrication.
4M40 is timing chains
First I dont think nissan sentra has a timing belt, I think it has a timing chain. I would go to www.TimingChainOrBelt.comto find out if it has a timing belt or chain.Are timing belts or chains better? I would say timing chains last longer.www.TimingChainOrBelt.com
Four-Cylinder has chains, V6 has belts.
A timing chain does not need to be replaced. Sometimes they can go bad and will make noise, or can get a bad link, requiring replacement. Timing BELTS require periodic replacement because they are rubber and wear out over time. Chains are good until they experience mechanical breakdown due to excessive wear.
chains
8th generation Civics (2006-up) have timing chains. Timing chains are more durable than timing belts. Unless there is a problem timing chains never get replaced; timing belts need replacing every 60,000 miles .
It has two timing chains...no timing belts
timing belt
No it has timing chains
On a 2007 Ford Explorer : The 4.0 liter SOHC , V6 engine has ( 3 timing CHAINS ) The 4.6 liter , V8 engine has ( 2 timing CHAINS )
Yes Timing Chains need to be replaced because they stretch out and Wear over time!
The factory timing chains have a lot more slack than the aftermarket chains.