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Distributor Cap and Rotor Replacement
 
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Pelican Technical Article:

Distributor Cap and Rotor Replacement

Steve Vernon

Time:

1 hour1 hr

Tab:

$7 to $40

Talent:

**

Tools:

Hands

Applicable Models:

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

Parts Required:

Rotor and distributor cap

Hot Tip:

Use care when pulling wires off

Performance Gain:

Cleaner running engine

Complementary Modification:

New spark plugs

The distributor cap and rotor will eventually wear out on your BMW2002. The metal contact areas take a beating. Misfires can also be a vacuum problem caused by cracks in both the rotor and cap; these are often very difficult to spot. If there are signs of pitting on the rotor or cap or they have over 30,000 on them they should be replaced. Checking them should be part of your regular maintenance.

The distributor, distributor cap and rotor are located on the rear right side of the cylinder head.
Figure 1

The distributor, distributor cap and rotor are located on the rear right side of the cylinder head. The rotor in the 2002 rotates clockwise, and the number one cylinder wire attaches at the 12 o'clock position (red arrow)

When changing the cap always follow each wire back from the spark plugs and label them for ease of re-installing them.
Figure 2

When changing the cap always follow each wire back from the spark plugs and label them for ease of re-installing them.

If you get the wires mixed up while transferring them the firing order is on the front of the valve cover.
Figure 3

If you get the wires mixed up while transferring them the firing order is on the front of the valve cover. Just remember that plug number 1 goes at twelve o'clock and rotates clockwise from there.

There are two metal clips that hold the distributor cap firmly in place (red arrows, one shown).
Figure 4

There are two metal clips that hold the distributor cap firmly in place (red arrows, one shown). To remove the cap, simply unclip the retainers with your hands, though the one on the backside is a little more difficult to access. If you cannot unclip them with your hands you can use a flathead screwdriver and gently pry the clip away from the cap.

Though it is almost impossible to stop micro cracks that can lead to misfires you should inspect the contact points inside the cap.
Figure 5

Though it is almost impossible to stop micro cracks that can lead to misfires you should inspect the contact points inside the cap. Normal wear and tear is fine (red arrow) but there should not be any large carbon deposits or signs of arcing against the inside of the cap.

Our distributor has been converted from the old points and condenser set up to a more modern unit.
Figure 6

Our distributor has been converted from the old points and condenser set up to a more modern unit. If your distributor is still old school you will see a set of "points" that open and close as well as a small condenser under the distributor cap. In either case there will be a rotor that is sitting on the top of the distributor shaft. It just pulls straight up and off.

There is a notch in the rotor (red arrow) that sits in the corresponding notch in the distributor shaft (yellow arrow) making it almost impossible to install the rotor incorrectly.
Figure 7

There is a notch in the rotor (red arrow) that sits in the corresponding notch in the distributor shaft (yellow arrow) making it almost impossible to install the rotor incorrectly. If the cap will not fit on after replacing the rotor the rotor is not sitting all the way down on the shaft. You will need to reposition it until it is correct and fully seated.

Check the contact end of the rotor for wear and tear (red arrow).
Figure 8

Check the contact end of the rotor for wear and tear (red arrow). This rotor is almost brand new. While you will see some wear there should be no signs of carbon build up or arcing.

Given the fact that we are working on the Clarion Build's BMW 2002 we expected a few upgrades.
Figure 9

Given the fact that we are working on the Clarion Build's BMW 2002 we expected a few upgrades. This photo shows where an inductive pick up (red arrow) has been installed eliminating the need for points and a condenser.

There are cut outs or grooves in the base of the cap (red arrows) that allow it to only be installed in one manner.
Figure 10

There are cut outs or grooves in the base of the cap (red arrows) that allow it to only be installed in one manner. If your cap is not sitting completely flush and tight to the distributor you do not have it seated correctly. I like to seat the new cap on the distributor and then transfer the labeled wires over from the old cap one at a time. Remember to never pull the wires by the actual wire part. Always remove them by handling the base of the connection. Pulling the wires can cause damage that will result in misfires and poor performance.


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Comments and Suggestions:
Dr. James Comments: 1993 325is coupe engine was working great. Now only cranks until the battery dies but never starts. This began after cowl area was sprayed thoroughly with water to remove leaves. Water was found in both front floor wells. Engine bay dried in the sun for weeks. Should I check distributor cap for moisture or the actual spark plugs I doubt? Fuse box was probably slightly damp but since completely dried. Any water damage to electrical that could cause this? Suggestions - help
September 10, 2016
  Followup from the Pelican Staff: Water damage can cause a no start. - Nick at Pelican Parts  

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Page last updated: Fri 12/9/2016 02:57:49 AM