Once you see the dirt inside, you'll be glad you did!
This one is a Bosch 0 237 304 016 from a Porsche '82 SC ('80-'83 are the same).
The '78-'79 distributors 0 237 306 001 are identical, except for the vacuum advance which is 1 237 122 035.
SC-distributors are very similar but, Carrera distributors are slightly different.
Items needed:
A small container to keep the parts.
Small circlip-pliers for external circlips. (Highly recommended!)
2 good-size flat screwdrivers 8-10" for prying.
Small drift and hammer.
3mm Allen key.
Oil and several rags.
Cleaning fluid and small brush.
No beer.
Set crank pulley to Z1, remove cap and just put it out of the way with wires in place. Check that rotor points to the notch in the distributor housing. To ensure that it is at the compression stroke, remove the valve cover left side and wiggle the intake valve; it should be lose! If not, turn the engine clock-wise 180 deg to Z1.
Remove hold-down nut and pull out distributor. It may be tight, pry on it; a small pry-bar using the short end under the distributor for leverage.
With the distributor out:
Remove the 2 clips for the cap.
Remove the small felt inside the shaft and ignore the screw inside.
Remove the Vacuum Advance Mechanism (2 screws) with a slight upward movement and wiggling the inside connector arm downward at the same time.
Remove the circlip on the shaft the easy way: With circlip pliers if it has the eyelets. Some circlips don't have eyelets; use 2 small screwdrivers carefully to remove it and don't let it fly into space.
With soft jaws, or small pieces of plywood, in the vice, clamp the distributor on its bottom.
With two 8-10" flat screwdrivers set across from each other on the edge of the distributor, pry under the Timer Core (811) with equal force upwards and remove it. It might be tight! Use some penetrating oil on the shaft. (WD-40 is NOT penetrating oil!)
IMPORTANT: Don't lose that very, VERY small dowel pin in the groove as the Timer core comes up!
Remove the second circlip from the shaft.
There may be additional washers on the shaft, save them and keep track for re-assembly.
Scratch a match-mark for reference on the Magnetic Pulse Generator (805) in relation to the notch in the distributor housing.
The 3 cut-outs (Notches) at the edge of the Magnetic Pulse Generator (805) are there so you can insert a 3mm Allen key. Use a light and turn the assembly if necessary to find the 3 Allen screws. Clean the inside of the hex with a piece of wire so the Allen key can go in all the way. Unscrew the 3 screws completely and lift out the whole assembly.
Now you'll see the weights and springs and all the dirt and grime!
Use your favorite cleaning fluid in a small container, submerge the distributor upside down and let it soak for a while. Use the small brush to clean the inside and weights thoroughly.
Clean all other parts.
I left the Magnetic Pulse Generator (805) and the Coil Section (807) connected for cleaning and oiling. Penetrating oil really gets into the bearing for cleaning, follow up with oil.
If things look good, oil the springs and pivot-points for the weights and re-assemble.
Oil the whole shaft on the outside.
Use the match-mark to install the Magnetic Pulse Generator but don't tighten the 3 Allen screws completely, just snug.
Install the circlip.
When installing the Timer Core, place the small dowel pin in its place on the bottom of the groove first, (Distributor on an angle in the vice, with the groove pointing up), then tap the Timer Core down with a small drift making sure that the roll pin stays in place. Use a little oil.
Install the last circlip.
Turn the shaft and make sure that the Timer Core rotates freely meaning: The star-tips do not touch the tips on the Pulse Generator.
Center the Pulse Generator before you tighten the 3 Allen screws.
It should spin freely now.
A few drops of oil in the shaft-center, replace the small felt plug, that's it.
Check the vacuum diaphragm.
With a line on the advance nipple, suck on it and watch the mechanism move.
Use your tongue to hold the vacuum for a few seconds. Good? O.K.
Install the distributor using the notch in the housing again for the rotor as a reference for installing; pulley still at Z1.
Start the engine; check and adjust the timing per specs.
Advance vacuum line connects in the rear of the TB.
Now put a grin on your face and tell your girl friend how good you are.
To complete the mission, test the ignition harness for leaks and the right resistance values:
The Beru plug connectors should show ~3k OHMS.
The short cap connectors are 1k OHMS.
Check each wire from end to end: ~4 OHMS total resistance; anything else means a problem.
I refurbished a couple distributor and found that the bushings, weights and springs were remarkably good even with 200k miles but the dirt in them is unbelievable.
I recommend the use of the dust shield (19) available on PP.
The axial play can be controlled by replacing/installing washers.
If you need to replace some washers under the pinion gear, remove it by carefully grinding the pin flush on one side and tap it out with a very small drift.
Mark the position of the gear on the shaft to be safe; use penetrating oil.
You can make a new pin out of long rivets, or nails, or buy a tight-fitting roll pin.
PP sells the pin, gear and vacuum advance for '78-'79 and '80-'83 as well as cap, rotor and signal cable connector (Pig-tail)