For the owners of the following vehicles: 325e or 325i e30 1984-91, 528e e28 82-88, and 525i e34 89-90

Check Your Timing Belts
These vehicles are fitted with the M20 six-cylinder in-line engine. This was the only engine BMW imported into the U.S. that utilized a timing belt rather than a timing chain. Many automobile manufacturers use the belt system with great success. Since the belts are fiber reinforced rubber they will fatigue and break if they are not replaced as part of a routine maintenance schedule.

What Happens if the Belt Breaks?
First let me describe what the timing belt does. The timing belt is a toothed belt that links the crankshaft to the camshaft. The camshaft is responsible for opening and closing the valves at a precise moment in relation to the position of the pistons, which are traveling up and down in the cylinders. With each rotation the pistons are traveling to the top of the cylinder, while the valves are closing. When the belt breaks the camshaft stops, several of the valves remain in the open position, and the pistons collide with the open valve. In many cases the valves will break off and destroy the pistons and the engine block. The car does not need to be traveling at highway speed. Should the belt break, damage will occur even at idle.

What to do to Prevent This?
There is no way to predict a belt failure. The only thing you can do is make sure you replace the belt every 60,000 miles. I recommend a visual inspection on every major service. Check for any signs of oil leaks in the cam gear area, or powdered bits of rubber or chips escaping from under the cam gear cover. Remove the cover and visually inspect the belt for surface cracks due to dry rot. If you have just purchased your vehicle or if you're not certain when the belt has last been replaced. Replace it now!

What could Cause Premature Failure?
The most common reason for an early failure is if the vehicles has an oil leak from either the cam seal, lower crank seal, or valve cover gasket and rocker shaft plugs. Oil saturation of the belt will quickly break down the rubber and fiber integrity of the timing belt, softening the teeth, which would allow the cam to jump timing. The same can occur if the water pump or one of the hoses were to leak on the belt for any length of time.

What should you Replace When Doing the Job?
The belt and the tensioner pulley are a must. Since the tensioner pulley is a sealed bearing, which spins at twice the speed of the crankshaft. The cam seal, valve cover gasket, and the 4 rubber rocker shaft plugs to avoid any chance of an oil leak onto the belt.

What should you Check for Additional Repairs?
The water pump should be a concern if it is very old or showing any signs of having leakage, the oil pump driveshaft gear seal if there are any signs of oil leakage, and the lower crank gear if there are signs of excessive wear and crank seal if there is an indication of a leak.

Early Style Stamped Sheet Metal Gears MUST be Replaced
All of the early model vehicles were original equipped with stamped sheet metal gears at the camshaft and at the oil pump drive shaft. The replacement units are manufacturer of a more durable sintered metal. (Below is a photo of a the sheet metal gears that failed at highway speed) The result was several bent valves and a cracked cylinder head. To determine if your vehicle has both late model sprockets I recommend a visual inspection. Many vehicles have been upgraded at the camshaft only. Some technicians who are not familiar with this problem may have installed a used sheet metal gear, not knowing this vehicle's cam gear failure issues. Anytime you remove the torx bolt on the cam or oil pump drive gear you must replace these bolts. Use lock tight on installation and torque to the specs in your Bentley manual.