Guys, thank you for your posts re interference and non-interference engines. I was never aware of these terms.

Let me share my experiences on 4D56 timing belt failure.

This engine has two timing belts, short and long belts. Short belt is driven by the crankshaft to synchronize the left and right balancer shafts. This minimizes engine vibration. Short belt failure rarely does any engine damage, except for increased vibration. Long belt synchronizes crankshaft, camshaft, and injection pump. From experience, long belt failure may or may not result in catastrophic engine damage, depending on the operating state of the engine during belt failure.

  1. Vehicle running fast or downhill, transmission engaged: When belt failure happens under this condition, injection pump and camshaft stop turning while crankshaft continues rotating due to vehicle momentum. Any valve which is in the open or down position will be repeatedly hammered by the piston, resulting in major engine failure.
  2. Vehicle running at low idle, transmission not engaged: When belt failure occurs under this condition, both camshaft and injection pump stop turning, and crankshaft almost immediately stops rotating. Although the piston may hit any open valve, the force is not sufficient to cause any significant damage due to low flywheel inertia.

Sad to say, most timing belt failures occur when vehicle is on the road with transmission engaged................

As Dusky posted, replace timing belts on schedule..