What's best - timing belt or timing chain?

What's best - timing belt or timing chain?
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Timing chain
TIming chains have been widely used before timing belts popularity explosion in 70's-80's.
As a general rule (not necessarily true today) timing chains are noisier, they are for sure require higher mechanics' qualification to maintain and they last much longer than a timing belts.
- Timing chain require a tensioner and if used for S(D)OHC - require a quieting shoe. In many cases one of them may serve both roles and two tensioner/quieter shoes could be used.
- Chain is usually heavier per inch length than belt and therefore require stronger infrastructure to hold it in place. In case chain get stretched over time and go above tensioner's adjustment capability things could go hairy fast. Engine's timing may become erratic.
- Timing chain in general is very reliable and require only every so often check-ups. Modern ECU could be capable of troubleshooting timing chain issues which increases reliability of the whole system.
- Timing chain usually enclosed within an engine case and constantly lubricated.


Timing belt
With introduction of a new materials in 60's and 70's it became feasible to have very dependable engine timing system that is light, easily serviceable and cheap at the same time.
- Timing belt drive usually quieter than a chain drive. Since belt is lighter it requires lighter support structures and does not need a calming shoe.
- As a result SOHC/DOHC engines could have higher RPMs without worry of an added chain momentum.
- Timing belt must be changed every 50-75 thousand miles along with the tensioner and a water pump if one driven by the timing belt.



In 2009 model year we see a new trend of car manufacturers moving back to timing chain engine design. Many of them rely on a service data and price/performance evaluation for the size of the vehicle.
It is unlikely that general public will know exact figures on timing belt/chain price/performance comparison but we all have our own preferences and that may become a driving force for the future engine models.