Replacing E31 Door Lock Cylinders

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Although I’ve been fortunate enough to NOT have to perform this procedure, I thought it was such an important topic and such a well documented post from “dmi” from Sweden on Bimmerforums.com, that I wanted to repost it here:

This How To shows the procedure for replacing the door lock cylinder. I am using a brand new uncoded cylinder but the general description can be used if swapping the cylinder for a used one. Note: the key for both the old and new cylinder is reqired when replacing with a used one. It is not a very difficult job but it is fiddly and requires some pacience.  When I bought my 850i the poor car had been molested by thieves who had destroyed both right and left door lock cylinder in their attemts to break into it. So I had to replace both locking cylinders but couldn´t find a good write-up or How To.

Parts needed:
Door lock cylinder 51 218 124 293 (same for both sides)

Contents of the pack:

The procedure:
1. Remove the door card and handle assembly.
2. The handle assembly with the old molested cylinder.

3. Remove the clip holding the lock switch cover using a flat screwdriver.

4. Lift the lock switch and drift the locking pin out using a hammer and a small nail with the point end cut off.

5. Insert the key into the cylinder and carefully (there is a spring and ball under the cylinder pressing on it plus the lock bottom piece) remove the cylinder by pulling the key.

6. Grasp around the cylinder to prevent the small locking plates from falling out. Slowly remove the key. The picture below shows how the locking plates looks when removing the key, they will push out of the cylinder body.

7. Pull each of the locking plates out and put them in the exact order that they where.

8. You should now have 1 unkeyed (closest to the outside of the door) and 12 keyed locking plates.
9. On each locking plate there is a tab with a number on it, lay out the new lock cylinder body and locking plates as the old one compare the numbered tabs to make sure.

10. Using the supplied grease, grease the new locking plates and springs. It should be a thin layer of grease. Insert the locking plate springs into the new cylinder body. And put the gasket on the cylinder body, it is the transparent ring on the cylinder body.

11. Now we have reached one of the fiddly parts, insert the locking plates while pushing in the key to keep the plates in place. The locking plates tab should be oriented toward the locking plate spring.

12. When all the locking plates are in, the key should be all the way in and the lock cylinder should not have any locking plates sticking out (just the first unkeyed one as shown on the picture below).

13. Replace the spring and ball in the handle assembly, put the lock bottom piece back so that the L-shaped part is pointing away from the assembly. Don´t worry it only fits one way. Put a thin layer of grease on the outside of the lock cylinder.

14. Now comes the really fiddly job, insert the lock cylinder into the handle assembly, note that the spring-loaded ball should make contact with the underside of outer edge of the lock cylinder.

15. While pushing the lock cylinder in, keeping pressure on the spring and ball, put the locking pin back and drift it back into position.

16. Test the new cylinder by turning the key both ways. If it feels OK the put the lockswitch back into position, place the lockswitch cover over it and put the holding clip back.

17. The new lock cylinder in place, just need to put it back into the door.

18. Job done! Enjoy the new lock cylinder and a beer! 

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About the Author:

I am an 8 Series nut. In 2009 I restored a '92 850i to peak condition and subsequently sold it - which left me depressed. So I embarked on catching my White Whale: this '95 850CSi Chassis #CD00166. I’m opinionated and swear constantly, but I have friends in spite of myself. I am funnier than my wife realizes. Please tell her. Cheers!

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