How to: Rebuilding the Eclipse / Excelsior Clutch. Rivets set with rivet sets
The Eclipse clutch was used by Excelsior as well as other American motorcycle manufacturers in the 19teens. The unit in my 1916 X was pretty well knackered, and ready for a rebuild. The metal plates had grooves worn into their mating surfaces, the tabs were worn and for some reason two of the plates had been riveted together into one assembly. The friction materials were in slightly better shape, but had worn thin and burn marks were apparent on both types of disks. Worst of all, the thrust plate had friction material that had worn deeply and split at the rivet heads. When riding, the clutch would not release cleanly, and grabbed and slipped when engaging. Brew a fresh pot of tea, it’s time for a session in the workshop:
First step was to source materials. McMaster Carr had the rivets, and Antique Motorcycle Works had the friction materials and plain discs in the correct thickness. Step Two was to deburr the metal discs with files and sandpaper, to prevent them from cutting into the friction material during use. Hand filing took a few minutes, but was much easier to control than using a bench grinder or orbital disc sander. Then the old trick of placing sandpaper face up on a flat surface, and rubbing the discs on the paper worked well to scuff up the plates, removing any roughness, steel bluing chemicals, etc. A quick session in the parts washer cleaned off oil that remained from the rolling and stamping manufacturing processes as well as the sanding dust.
Step Three was to attach a friction disc onto the thrust plate. After drilling out the old rivets, deburring the holes and cleaning the plate, it was ready to receive the new clutch material. After clamping them together, the rivet holes were drilled, using the holes in the thrust plate as a drill jig. Be sure not to drill the holes oversize, rivets need to be a snug fit. Tape held the material down while I used a countersink to cut clearance for the rivet heads. Be sure to choose your rivets and your c’sink to have the same angle. Many varieties are available, but they need to match to give a good fit on the rivets. If they were to come loose, there would be some real trouble inside your primary cases.
An important point here: Be sure that the heads of the rivets sit well down into the countersink, below the top surface of the friction material. That material will wear, and eventually those rivet heads will rub on the metal disk. Then you’ll have to this job all all over again. So set them down far enough to get a decent amount of life from the material, but not so deep that the c’sink breaks through the back of the friction material, allowing it to tear in use.
How to install rivets? We shouldn’t use cheap aluminum Pop rivets in these applications, but it isn’t hard to do it the old fashioned way. If you have never worked with old style rivets, don’t fret. First fit the rivets into the holes in both pieces to check the fit. Then trim the rivet tails to be about 1/16” to 1/8” longer than the joint. The rivets will be deformed by hitting them with a punch on the head and a rivet set on the tail.
Now, off to the lathe to quickly whip out a rivet set:
A rivet set is a simple tool, just a bit of steel with a countersunk hole to shape the tail of the rivet. The photo shows the general shape, just as the parting tool is about to cut it to length. If you plan to make a set a lot of rivets, you can harden the tool, but I just used mild steel for this setup. To set the rivet, be sure that the two parts are clamped together tightly, or the rivet will lock them with whatever gap is present. Peen over the tail of the rivet with a light hammer, and then use a small sledge hammer and your new rivet set to really deform the tails into a clean ball / cone shape. If you find that one of the rivets isn’t quite right, you can remove them by milling or grinding off the tail, and punching the rivet head out of the part. You can try to drill them out, but you may find that the rivet just spins in place.
That’s it. Repeat as necessary. The re-assembly process of the clutch is just like the disassembly, but backwards.