One of the routine maintenance items that you should perform on your BMW is the checking and replacement of your accessory drive belts. The belts are driven off of the crankshaft and power accessories such as the water pump, power steering pump, alternator and air conditioning compressor. There are typically two belts on the car - one that powers the air conditioning compressor and another that powers everything else. Both should be checked periodically (every 3,000 miles, or when you change your oil), and particular attention should be paid to the main belt. The car can run fine without the air conditioning belt installed.
Some of the early E30 cars use a standard v-belt design, and some of the later cars use what is known as a poly-ribbed belt (having many channels or ribs on the underside of the belt). The poly-ribbed belt setup utilizes a spring-loaded belt tensioner pulley that provides the proper tension for the belt at all times, making adjustment unnecessary. The traditional style v-belts need to be tensioned using standard types of clamps and tensioners.
When inspecting your belts, the one thing that you want to look for is cracks (yellow arrow - Figure 1). If you see any cracks at all, you should replace your belts. The cracks will usually occur on the inside of the belt (the surface that typically rides on the surface of the pulley). With the poly-ribbed belts, this is the grooved surface. With the v-belts, this is the surfaces on the legs of the 'V'.
With the poly-ribbed belts, replacement is a snap. The tensioners that hold the belt tight can be easily released using a socket and or 8 mm hex tool. Different tensioners turn different directions, so you may have to rotate the tensioner clockwise or counter-clockwise depending upon your particular car. The description of this process is one of those things that is difficult to describe, but very easy to do. First, pry off the small plastic cap that covers the tensioner (green arrow Figure 1). Then, place your tool into the tensioner and try rotating clockwise or counter-clockwise - will become immediately apparent how the tensioner releases the belt (Figure 2 and Figure 3).
Removal of the two belts is easy - you do not have to remove the fan. Simply release the tension on the belt from the tensioner, and then the belt should simply slide off. Release the tension, and then you should be able to unwind the belt from the engine. The belt should be able to be maneuvered around and through the fan - you do not need to remove the fan to swap out any of the belts (Figure 4).
It is important to note that if your BMW has air conditioning, you will need to remove this belt first, as it typically blocks the other belt. Another tip - if the belt is worn, simply snip it with some large tin cutters and pull it out of the car, after you have released the tension on it.
Installation of the new belt is easy. Simply slide on most of the new belt onto the pulleys, release the tension on the tensioner, and slide the belt onto the tensioner. Check to make sure that the belt is securely seated in all of the pulleys. Verify that the ribbed portion of the belt is set against the crankshaft pulley. The proper orientation of the belt is shown in Figure 5.
Replace any plastic caps that you may have removed from the front of the tensioner pulleys. Now, start the car and peek in at the belts. Verify that they are turning smoothly on all of the pulleys.
For engines with the older-style v-belts, the procedure is nearly identical, except for the tensioning. The alternator is mounted on a bracket that rotates and is used to keep tension on the belt. In addition, there is a small rack-and-pinion device on this bracket that allows you to crank up the tension on the belt (Figure 6). The first step in setting or releasing tension is to release the nut on the back of the bracket that keeps the whole assembly secure. Do not attempt to turn the geared bolt without first releasing this nut on the rear - you will most likely damage the bracket. With the nut released, you can now turn the geared bolt counter-clockwise, releasing tension on the belt. Belt replacement is nearly identical to the poly-ribbed belts.
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