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Alternator Replacement
 
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Pelican Technical Article:

Alternator Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$130 to $150

Talent:

**

Tools:

(2) 13mm, 10mm, 8mm wrenches

Applicable Models:

BMW E10 2002 Coupe/Conv (1967-76)
BMW E21 320i Coupe (1977-83)

Parts Required:

Alternator

Hot Tip:

Do not over tighten the drive belt

Performance Gain:

Proper running accessories

Complementary Modification:

Change the belt

One of the nice things about the configuration of the BMW 2002 engine is the relative ease with which you can replace the alternator. The alternator is nestled neatly on the left side of the engine compartment and is easily accessible. The replacement and repair process is straightforward and should take you two hours at the most to complete.

First, make sure your alternator is indeed the cause of the problems with your charging system. Sometimes bizarre electrical problems can be caused by a number of faults other than the alternator. It's important to troubleshoot the system prior to replacing your alternator.

The first component to check, then, is the belt that drives the alternator. Is it tight and optimally turning the accessories? If not, tighten it with around one-inch of deflection midway between the alternator and water pump. Do not over tension the belt, as the 2002s are known for destroying the water pump pulley and pump by over tensioning the belt. Modern belts seldom break, but they do get brittle and glazed with age, and can slip on their pulleys. Replace it with a new one if it looks cracked or brittle.

The next item to check is the voltage at the battery. This should read a little more than 12 volts with the engine off. When the car is running, the voltage should read in the range of 13 to 14.5 volts with the engine at 2,000 rpm. If your battery appears to be leaking, your voltage regulator has probably failed. The battery will usually only leak acid if it has been overcharged at a much higher voltage. If the voltage measured at the battery is more than 16 or 17 volts when the engine is running, the regulator is probably bad. If your battery has boiled over and has acid flowing out the top, clean it up immediately. Dousing the area with a water-and-baking-soda solution should help considerably to neutralize the acid and prevent it from eating away at the metal.

An important item to check on your car is the engine ground strap. The engine is electrically isolated from the chassis by rubber motor mounts. If the engine ground strap is missing or disconnected, you might have a whole bunch of problems, including electrical system malfunctions and difficultly turning over the starter. Please see our article on battery replacement. Also the BMW 2002 alternators have an external ground that may become faulty.

The 2002 has a replaceable voltage regulator/brush assembly. If you've determined the voltage regulator to be working properly, then you should probably remove the alternator for testing and inspection. If your voltage regulator is the problem, please see our article on voltage regulator replacement. Before starting any work, make sure you disconnect the battery. The positive battery terminal is directly connected to the alternator, and it can be dangerous to work on if it's live.

You begin by removing the drive or accessory belt.
Figure 1

You begin by removing the drive or accessory belt. The tension on the belt is determined by the adjustment bracket on the alternator (red arrow). Loosening the alternator will allow you to remove the belt. You are going to be working close to the radiator. If you are worried about damaging it, like we were since we are working on the Clarion Build's BMW 2002, and we have a really nice aluminum radiator, put a piece of cardboard over it to protect the cooling fins.

The belt travels around the crankshaft pulley on the bottom of the motor (red arrow), around the water pump (yellow arrow) and over the alternator.
Figure 2

The belt travels around the crankshaft pulley on the bottom of the motor (red arrow), around the water pump (yellow arrow) and over the alternator. You do not need to get under the car to replace it this photo is for illustration purposes. Just make sure the belt is sitting in the pulleys correctly when reinstalling.

When working with the alternator it is a really good idea to disconnect both the positive (yellow arrow) and negative (red arrow) cables from the battery.
Figure 3

When working with the alternator it is a really good idea to disconnect both the positive (yellow arrow) and negative (red arrow) cables from the battery. At the very least remove the ground or negative cable and place it so that it cannot accidentally come in contact with the battery post while you are working. I personally remove both cables to be safe.

You will need to loosen the alternator first.
Figure 4

You will need to loosen the alternator first. Start by using two 13mm wrenches or sockets and loosen but do not remove the 13mm nut and bolt where the alternator connects to the mount on the block (red arrows).

Next, loosen but do not remove the two 13mm nuts and bolt on the adjustment bracket (red arrows).
Figure 5

Next, loosen but do not remove the two 13mm nuts and bolt on the adjustment bracket (red arrows).

Gently push the alternator down and slide the belt off the alternator pulley.
Figure 6

Gently push the alternator down and slide the belt off the alternator pulley.

You can now remove the alternator mounting hardware and tilt the alternator forward, making sure it does not come in contact with the radiator.
Figure 7

You can now remove the alternator mounting hardware and tilt the alternator forward, making sure it does not come in contact with the radiator. Unplug the exciter wire (red arrow). Use a 10mm wrench and remove the power cable (yellow arrow) and then use a 8mm wrench and remove the ground wire (green arrow). Now safely and carefully remove the alternator from the engine bay.

Before installing the new alternator inspect the ground wire form the alternator to the engine block (red arrows).
Figure 8

Before installing the new alternator inspect the ground wire form the alternator to the engine block (red arrows). This ground wire can be the cause of a faulty alternator so make sure the contact points are clean and secure.

Installation is the reverse of removal.
Figure 9

Installation is the reverse of removal. When reinstalling the drive belt make sure you do NOT over tension the belt. The 2002 is known for destroying water pumps by having too much tension on the pulley and belt. Tension the belt so the water pump turns but is not over tight. You should be able to deflect the belt about an inch in the midway point between the alternator and water pump.

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Page last updated: Mon 12/5/2016 02:57:16 AM