Hello JK,
There are many opinions on the service interval. I believe the factory service interval is 60,000 miles with no mention of time.
Since a timing belt failure can require a $5000 or more repair job to fix bent valves, a little insurance is in order. Common wisdom is to replace the belt every 7 years if the mileage limit isn't exceeded because rubber ages and deteriorates. Many people replace it at fewer miles than 60,000. It al varies - extreme usage would call for a replacement at fewer miles. Is the car driving at Autobahn speeds or on the track? Is it driven in extreme cold or hot temperatures?
Another concern is the water pump. The labor to replace the water pump is a small addition when everything is opened up for the timing belt change. Many people automatically change the water pump when the belt is changed even if there is no sign of bearing wear or water leaking. My mechanic recommends replacing all the water pump bolts so they can be accurately torqued and are less likely to break off during a future service.
When replacing the belt inspection and repair of the misc. tensioner parts should be done. The roller bearings should be replaced.
Rich
Membership Chairman
Charter Member
1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed rescue
1979 928 5-liter track beast