After 80,000 kilometres tensioners and seals are more likely to fail (especially after installation and adjustment of new belt).

Labour costs associated with belt replacement are expensive, so it makes economic sense to replace all components at the same time.
A worn or loose pulley can cause belt problems.

Worn seals can lead to oil leaks contaminating the timing belt and reducing its life.

Normal tensions cannot be maintained to assure proper life of replacement belt.

Internal bearing wear is not noticeable.

Pack/Kit contains OEM spec components to ensure it meets OEM Warranty intervals. (Refer to manu-facture's hand book for recommended intervals).

OEM's recommend as part of normal preventative maintenance