Because you would complain about the cost of such a belt. No one makes belts that last forever. They're rubber and they flex a huge amount up to a dozen times per revolution, and they dry-rot just from sitting. The better question is how can they make a belt to last so long?
You didn't list your engine size so I can't look up if you have an "interference" engine. Most import engines are of that design. If the timing belt breaks that results in bent valves which is a real expensive repair. All manufacturers recommend the belt be replaced at specific intervals to avoid that repair. Back in the late '80s Honda used to recommend the belt be replaced every 75,000 miles, ... And they typically broke at 65,000 miles. My old beat up '88 Grand Caravan with 402,000 miles is on its first replacement belt but that is not an interference engine so if it breaks it's not a big repair bill. Yours COULD last just as long as my original one did, but at $1000.00 to $3000.00 for a valve job, do you want to risk it or do you want to do some preventive maintenance?
Keep in mind the city miles you mentioned puts a real lot more wear on the timing belt than highway driving. The engine makes a lot more revolutions in a given mileage because it spends a lot of time idling at red lights, and when in first and second gears. Highway driving is the least stressful on the belt.
Thursday, June 6th, 2013 AT 2:30 PM