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As of this writing (2003) a distributor cap for a M189 motor is about $300. It may make sense to renovate an old one. Note also that a 280C cap will work on a M189 motor with some modifications. Most of us just buy new parts periodically, but Danny Rearden says, "High tension ignition components such as distributor caps and rotors are generally only faulty if they are cracked, or have carbon tracks on the surface. Even both of these conditions are usually repairable if you are prepared to invest a few hours. My dad specialized in repairing obsolete vintage and racing ignition systems and magnetos where parts were completely unobtainable." Clean the part, first with solvent cleaner, then with strong hot detergent solution and dry thoroughly. Inspect very carefully, with a magnifying glass if your vision is not 20/20, looking for any surface marks which were not intended to be there. If there is no visible sign of high voltage tracking, go to polishing. Otherwise use a hobby knife and scrape the surface until you get to totally clean material, even if this means making a hole in the component. Grooves and holes can filled with epoxy filler. We always used [Bristish] Epiglass Low Density Filler, designed for boat repairs. It seems to have very good thermal and electrical properties, and it does not run while curing. File and sand the repair back to original profile. Polish out any marks (both in the original part and any repair), using abrasive paste, such as perspex[plexiglas/acrylic] polish or cutting compound. These surface marks, if not removed, will be future failure points. If the part has a dull, porous look to the surface, a light spray of a suitable clear paint may be in order, but don't overdo it. If the repairs were to a visible part, then coloured paint can be used. In the 25 years my dad was doing these repairs, I can only recall 1 or 2 items failing again, out of several hundred, and these were subject to 'owner abuse'.
The important things are: Frank Mallory adds: He failed to mention that you should check the carbon brush in the center of the rotor. They do get worn down, and in one car I worked on, it was missing entirely. There is no repair for this, save possibly scavenging one from another cap. Also, many of our cars use rotors with resistors. These should be checked with an ohmmeter, and again a repair is very difficult (tho in one case I soldered a bypass wire to the top of the rotor to get the car running, when a replacement rotor was not readily available). |