Mazda MPV 1999-06

Timing Belt

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General Information



Interference Engines

Engines, chain- or belt-driven, can be classified as either free-running or interference, depending on what would happen if the piston-to-valve timing is disrupted. A free-running engine is designed with enough clearance between the pistons and valves to allow the crankshaft to rotate (pistons still moving) while the camshaft stays in one position (several valves fully open). If this condition occurs normally, no internal engine damage will result. In an interference engine, there is not enough clearance between the pistons and valves to allow the crankshaft to turn without the camshaft being in time.

An interference engine can suffer extensive internal damage if a timing belt fails. The piston design does not allow clearance for the valve to be fully open and the piston to be at the top of its stroke. If the belt fails, the piston will collide with the valve and will bend or break the valve, damage the piston, and/or bend a connecting rod. When this type of failure occurs, the engine will need to be replaced or disassembled for further internal inspection; either choice costing many times that of replacing the timing belt.

Inspection




NOTE
For manufacturer-s recommended service interval, refer to the maintenance interval chart located in this manual.

The average replacement interval for a timing belt is approximately 60,000 miles (96,000 km). If, however, the timing belt is inspected earlier or more frequently than suggested, and shows signs of wear or defects, the belt should be replaced at that time.


WARNING
Never allow antifreeze, oil or solvents to come into with a timing belt. If this occurs immediately wash the solution from the timing belt. Also, never excessive bend or twist the timing belt; this can damage the belt so that its lifetime is severely shortened.



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Fig. Never bend or twist a timing belt excessively, and do not allow solvents, antifreeze, gasoline, acid or oil to come into contact with the belt

Inspect both sides of the timing belt. Replace the belt with a new one if any of the following conditions exist:



Hardening of the rubber-back side is glossy without resilience and leaves no indentation when pressed with a fingernail
 
Cracks on the rubber backing
 
Cracks or peeling of the canvas backing
 
Cracks on rib root
 
Cracks on belt sides
 
Missing teeth or chunks of teeth
 
Abnormal wear of belt sides-the sides are normal if they are sharp, as if cut by a knife.

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Fig. Clean the timing belt before inspection so that imperfections or defects are easier to recognize



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Fig. Inspect the timing belt for damage, such as a broken or missing tooth, which may be due to a damaged pulley



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Fig. Back surface worn or cracked from a possible overheated engine or interference with the belt cover



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Fig. Side wear from improper installation or a defective pulley plate



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Fig. Worn teeth from excessive belt tension, camshaft or distributor not turning properly, or fluid leaking on the belt

 

If none of these conditions exist, the belt does not need replacement unless it is at the recommended interval. The belt MUST be replaced at the recommended interval.


WARNING
On interference engines, it is very important to replace the timing belt at the recommended intervals, otherwise expensive engine damage will likely result if the belt fails.

 
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