This distributor has had a special washer fabricated to spread out the tightening force and prevent indentation into the softer aluminum of the distributor body. Nice.
Note that the hole in the plastic insulator is not centered (top to bottom). The hole is closer to the bottom. If you flip it around, it will not fit properly. Also note that the bolt is shaped such that it will fit the insulator in a keyed fashion.
Using a needle nosed pliers, remove the plate as shown. DO NOT GRAB THE POST ON WHICH THE POINTS PIVOT! Doing so will scar the pivot and the points will not pivot smoothly. Wiggle it back and forth until the plate is free.
Remove it. Please note that this distributor was set up to use two of the shorter, eight coil advance springs. Mark Etheridge of Moto Guzzi Classics likes this modification. From the factory, one shorter eight coil spring and one longer nine coil spring were used.
Remove the advance mechanism. When you pull it up, a small ball bearing and the spring behind the ball bearing will fall out. Be careful not to loose these tiny pieces.
Remove the pin that secures the gear to the shaft. From the factory, this pin is solid and peened at both ends. This roll pin was replaced during a previous rebuild. Comparatively speaking, roll pins are very easily removed. The solid pins can be difficult. Please reference the techniques elsewhere on this page for guidance on removing the solid pin.
Then the shimming washer (nearest the drive gear) and the spacer washer (furthest from the drive gear). Typically the shimming washer is much thinner than the one shown. However, this distributor was previously rebuild and this shimming washer was fit in place.
Here is the rotating shaft with the bakelite washer and a thin flat washer. Note that the bakelite washer is furthest from the top of the rotating shaft; the thin flat washer is positioned at the top of the shaft.
Note these spiral cuts. The purpose of these cuts is to direct oil back down into the engine to help prevent oil from migrating into the top of the distributor body.
Hold down the tiny ball bearing and spring with your finger and then slide the advance mechanism over the ball bearing, moving your finger back as the advance mechanism moves over the ball bearing.
Slide the advance mechanism fully in place such that the longer pin fits into the hole in the plate. Both pins will also interface with the slots in the advance weights.
You can see the longer pin through the bottom hole. This longer pin limits the total advance and prevents the advance weights from jamming against the sides of the distributor body, should the advance springs break.
Thanks to Dan Eberhardt for sending me this additional information about the felt he uses:
I have some more useful information to pass along regarding the type of felt to use for the distributor shaft. Several years ago I was able to buy felt at the local hobby stores (Hobby Lobby, Michaels etc.) that wasn't the best but did work for the distributor shaft. However, I purchased some recently and had to replace it in just a few miles and thought maybe I misaligned it when installed so installed another one only to have it begin passing oil in just another few hundred miles. Took the distributor apart again very carefully and the felt was located properly but it was evident that it was not expanding like a felt seal should! Did some research and discovered quality felt should contain mainly wool. McMaster-Carr to the rescue once again (Part #8334K35). It is 1⁄16 inch thick, has a durometer of 35A and a tensile strength of 500 PSI and only costs USD $10.46 for a 12 inch × 12 inch sheet. The seals fit well when cut to 16 mm × 45 mm.
Here's an original old seal on the left with thousands of miles and here's a new seal on the right made with Craft Store felt after just a few hundred miles along with some seals made from the Good Stuff.
Cut the felt to size. You'll note the new piece is longer than the old piece. The old piece did not fully wrap around the shaft. This is common after 40 years - the old felt shrinks. The felt can also become stiff, full of rust, etc.
Fit additional shims under the drive gear to achieve a clearance of 0.1 mm to 0.15 mm (~0.004 inch to ~0.006 inch). Every distributor that I've rebuilt has had way too much clearance. Shimming the shaft properly is an important step.
Tools I use to check the clearance. The ice pick is a great size to get close to the needed shims prior to fitting the roll pin. Final adjustment is done with the actual roll pin.
I like to replace the original fasteners with stainless replacements. Here is my lifetime supply of distributor related pieces and parts (including replacement bakelite washers!). I made the replacement bakelite washers using modern Garolite material that I purchased (McMaster-Carr part number 8667K111).
On the side with two threaded holes, I fit the spring clip and condenser as shown. I prefer the spring clip to face this direction as I find it much easier to move into place when the distributor is mounted on the engine case.
On the side with one threaded hole, I fit the spring clip as shown. Again, I prefer the spring clip to face this direction as I find it much easier to move into place when the distributor is mounted on the engine case.
Fit and tighten the nut. I use both a flat washer and a lock washer under the nut. Tighten securely, but do not over tighten and break or deform the plastic insulation.
Secure the distributor body to the distributor base with the bolt and washer as shown. Again, a special washer was fabricated to spread out the forces on the soft aluminum of the distributor body. A very worthwhile upgrade.
