I recently discovered that the centrifugal advance in my 350SL distributor was not working. Found this out by hooking up timing light and rotating distributor - timing mark that I had painted on balancer did not move!
I tried to find a used replacement but nothing worked out. So, I decided to dismantle and find out what was wrong.
Others may want to do this, so this is a method that should apply to any early V-8s. (Please feel free to comment!)
Firstly mark exactly where your rotor is pointing - rotate it back & forth and check and mark the range. Also mark exactly where the hold down bolt is in it's slot. (MB says to set engine at TDC on #1 so that rotor centreline is pointing to the TDC mark on the distributor base. They don't say anything about the cam positions, but if you look through oil filler cap, the two lobes should be pointing up. - I skipped doing this, but it IS a good idea)
To remove the distributor, first remove the cap and lay it back on engine with wires still attached. Then, use an extension (preferably magnetized) to remove the holddown/adjusting bolt on the left side. It has a hex socket (allen key) - I had to cut off an allen key and tape it into a small socket, then use a socket extension to reach the bolt). I stuck a small magnet near the end so the bolt would not fall into one of those unreachable spots! Once the screw is out, just lift the distributor out - You will need to disconnect the thin green wire and unplug the main cable.
Once out, put in your vice and check it out.
I first removed the trigger points. Once out, I cleaned them using a small piece of cardboard. But they looked in great shape for 30-somethings. I then set them aside.
I then removed the vacuum unit - Just two screws and a little circlip at the end:
Next, I removed the points, condenser, the side clips, noting which one goes where(taller one is at slot) and all the screws (note which goes where - they are different lengths). This exposes the upper distributor plate.
The black thingy at 4 oclock, is a spring clip that keeps the upper and lower plate together. There is a ballbearing under the inner end. If you can pry this out without losing it, the clip will be loose and you can remove it now or in next step.
Now, if you rotate the upper plate a bit to miss obstructions, you can lift it off. It will still be attached to the lower plate by a short piece of grounding wire, so let it hang while you move to next step
Next step is to remove lower plate. hard to see in picture, but there are two small protruding ledges at the distributor wall that keep the plate in position. The plate may be stuck and need some encouragement, but what you need to do is rotate it so that the ledges line up with the gaps near the edge of the plate and then it will lift out - May have to pry it a bit from underneath. Now you have both plates out:
This exposes the centrifugal weight mechanism. I did not attempt to disassemble this. I am told it will come apart but I did not want to damage it trying:
You should be able to pull the weights outwards and have them spring back. In my case, the whole thing was seized up and could hardly be moved.
I soaked the whole distributor overnight in kerosene. Then I gave the area several shots of Releaseit and other similar products. Eventually, everything loosened up.
There should be a very thin fibre shim under the weights - presumably to reduce friction and wear as the weights swing back & forth. In my case, this shim was fractured in several places. I opted to eliminate it - what else could I do seeing I was not dismantling the weight assembly? I attempted to correct for this by spraying with some Teflon lube. I will probably check each Spring that advance is working and if it isn't I will know where to look!
Next was to reassemble everything and re-install. One tip - use the black ball bearing clip to hold the two plates together and install them at the same time.
Be VERY careful how you re-install the distributor on the engine. You need to start it with it turned slightly anticlockwise from where you want it. Also make sure the screwhole is at original place in holddown/adjustment slot. The distributor will rotate a bit as it goes down and will hopefully point to the marks you made. Screw it down exactly where it was and rotate the rotor back and forth just to be sure you got it in the right place (I did not and it gave me some grief!).
Set the points to about 0.014", replace the distributor cover, crank her up and see if she goes!
Hook up your timing meter with vac advance plugged (used golf tee). Then vary rpm from idle to 3000 rpm and check that the mechanical advance is now working. Finally check dwell, readjust if need be and then do a final timing setting. I chose to set to 30 deg BTDC at 3000 rpm.
Please note that I am a first timer at this, so don't blame me if you screw up! I did get some advice from experts, but only by email. If others see errors or have comments please add so others can benefit.
Hope this helps someone!
Added these pictures after doing second (spare) distributor:
1. ONE WEIGHT IN PLACE
2. INNER SPINDLE
3. Screws for REMOVAL of WEIGHT PLATE (I did not remove them)
4. SPRING CLIP - There is a washer under this clip and a felt pad above. My clip was loose - I am told it will release if you pry under weight plate - Replacing it requires some dexterity and ingenuity!
5. WEIGHTS
6. CAM - this fits over inner spindle
7. FIBRE SPACER - breaks if you look at it - i lubed surface with Teflon spray and did not replace this - need something that is heat and oil resistant - Teflon would be good because weight slide on this. I put small brass washers under weight spindles to reduce friction.
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