Timing Belt Tensioner Failure — What Happens
Photo documentation of engine damage caused by timing belt failure when the timing belt tensioner roller stud sheared flush with the block, including bent exhaust valves and piston damage.
This is what happens when the timing belt fails. In this case the timing belt tensioner roller stud sheared flush with the block, causing immediate belt failure and severe engine damage.
Warning: The 944 timing belt and tensioner are critical maintenance items. Belt failure on a 944 causes piston-to-valve contact, resulting in the damage shown below. Follow all recommended inspection and replacement intervals.
Cylinder Head Damage
Side view of the cylinder head after the timing belt failure. All four exhaust valves are bent. The #4 exhaust valve (front of the head) sustained the most severe damage — the valve stem is visibly distorted.
Piston Damage
The tops of the pistons showing the damage. Note the gouges from the exhaust valves in the lower right-hand corner of the dish area of each piston.
Valve Comparison
Five exhaust valves side by side. The center valve is a used stock 944 Turbo exhaust valve — it has some stem deposits but is straight. The two valves on each side are the bent valves removed from the cylinder head after the failure.
Tensioner
The tensioner assembly as it came out of the engine. The retaining nut visible on the back side of the tensioner is one of the retaining nuts for the oil pump. At the time this photo was taken, approximately 1 inch of threads from the sheared stud remained in the block.