Checking Distributor Health - Bosch Distributor
This is old school information. BMW has not used a distributor since 1981. But many of these distributor-equipped cars are still around and I want to make sure this information does not get lost.
Make sure the point cam is lubricated with proper grease. You need to use a specific Distributor Cam Grease.
Set point gap with a dwell meter
Set dwell to the low end of specification because point cam follower wear will increase the dwell reading over time.
For example, the BMW 2002 specification is 59-65° so set to 60 ± 1°
Note this is especially critical on 2002tii where the spec is 60 ± 1°
Check for proper (free) movement of the centrifugal advance by turning the rotor in the advance direction. It should move freely against spring tension.
If it does not move correctly, you will have to remove the points plate to inspect for what is wrong - broken spring or rust on the pivot point of the weights.
Remove the distributor rotor and lubricate the felt pad in the center of the distributor shaft with two drops of light oil (i.e. Marvel Mystery Oil).
If the distributor has a vacuum advance and/or retard diaphragm, use a vacuum pump to test both for movement of the points plate when vacuum is applied and that the diaphragm holds vacuum - on each of the vacuum ports.
BMW gives its timing specifications for a raised RPM, typically 1700 or 2200 RPM. When checking the timing, make sure the timing mark is stable (i.e. that it does not jump around). This is essentially a check of wear on the distributor shaft.
Also check to see that full centrifugal advance can be reached. this is easiest to check with a timing light with an advance display.
On cars that have a timing plate at the front cover, make sure you do not confuse ATDC with BTDC.
Note: Thank you Danny Walford for creating the illustrations used here.