BMW Cars 1999-06

Timing Belt

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WARNING
Timing belt maintenance is extremely important! The 325i models utilize an interference-type, non-free-wheeling engine. If the timing belt breaks, the valves in the cylinder head may strike the pistons, causing potentially serious (also time-consuming and expensive) engine damage. The recommended replacement interval for the timing belt is 50,000 miles (80,000 km), or every 4 years if not sooner. Refer to Section 3 for information on servicing the timing belt.

Although most of the BMW models covered herein use timing chains to drive the camshaft(s), a timing belt is used to drive the camshaft on the M20B25 engine. These engines were installed in the BMW 325i models and available through model year 1993 in production of the E30 series 325i Convertible.

The timing belt should be checked during each service and replaced as follows:



If damaged or contaminated by fluids or debris
 
If removed for any reason to perform another repair
 
If the last replacement interval cannot be determined
 
Every 50,000 miles (80,000 km) or every 4 years
 

General Information



Timing belts are typically only used on overhead camshaft engines. Timing belts are used to synchronize the crankshaft with the camshaft, similar to a timing chain on an overhead valve (pushrod) engine. Unlike a timing belt, a timing chain will normally last the life of the engine without needing service or replacement. Timing belts use raised teeth to mesh with sprockets to operate the valvetrain of an overhead camshaft engine.

Whenever a vehicle with an unknown service history comes into your repair facility or is recently purchased, here are some points that should be asked to help prevent costly engine damage:



Does the owner know if, or when the belt was replaced-
 
If the vehicle purchased is used, or the condition and mileage of the last timing belt replacement are unknown, it is recommended to inspect, replace or at least inform the owner that the vehicle is equipped with a timing belt.
 
Note the mileage of the vehicle. The average replacement interval for a timing belt is approximately 60,000 miles (96,000 km).
 

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 were 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



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. 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



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Fig. The timing belt on the left hasn't started to separate like the belt on the right which is beginning to separate and is ready for replacement



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Fig. Check for premature parting of the belt



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Fig. Check if the teeth are cracked or damaged



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Fig. Look for noticeable cracks or wear on the belt face



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Fig. You may only have damage on one side of the belt; if so, the guide could be the culprit



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Fig. Foreign materials can get in between the teeth and cause damage



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Fig. Inspect the timing belt for cracks, fraying, glazing or damage of any kind



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Fig. Damage on only one side of the timing belt may indicate a faulty guide



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Fig. ALWAYS replace the timing belt at the interval specified by the manufacturer

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.


NOTE
For manufacturers 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 (96,000km). 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.



Click image to see an enlarged view

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
 

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.



Click image to see an enlarged view

Fig. Broken tooth 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



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

Removal & Installation




NOTE
The radio may have a coded theft protection circuit. Obtain the code before disconnecting the battery, removing the radio fuse, or removing the radio.


CAUTION
Timing belt maintenance is extremely important. All Hyundai models use interference-type non-freewheeling engines. Should the timing belt break in these engines, the valves in the cylinder head will come in contact with the pistons, causing major engine damage. The recommended replacement interval for timing belts is 60,000 miles.


CAUTION
On models with an air bag, wait at least 90 seconds from the time that the ignition switch is turned to the LOCK position and the battery is disconnected before performing any further work.

 
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