OHV alternator rotor repair by Bill Taylor
OHV alternators have an inherent weakness: the field winding is not solidly bonded to the rotor. Acceleration and deceleration cause the rotor winding to shift slightly. This can eventually break the wire, usually where it leaves the winding to connect to the slip ring. Although replacement rotors aren't very expensive, they can usually be repaired without too much trouble. Here's how:
Remove the rotor from the alternator. Next, remove the back half-pole; it's friction fitted on a splined shaft. Ideally this should be done using a vice or press, but it can be done with a mallet, taking care not to damage the shaft. This is important, as the inside of the rotor's shaft is a tapered fit to the engine, and the outside of the shaft mates with an oil seal.
Here is the rotor with the half pole removed. The arrow shows where the wire is broken.
Unsolder the wire from the slip ring, and unwind one turn.
Feed the wire through the hole leading to the slip ring, trim it to length and remove the varnish in preparation for soldering. Protect the wire where it passes through the pole, using either the original fibreglass insulation, or heat-shrink tubing as shown.
Ready to solder to the slip ring.
After soldering and cleaning up.
Finally, reassemble the half pole. Ideally, the coil should be coated in Glyptal insulating paint. This will prevent movement of the coil or its connections to the slip rings, insuring the same failure will not re-occur. Use a generous coating, and after drying, cure it in an oven for 2 hours at 125C.
Final assembly with the repaired rotor. While the rotor is off, you can replace the front oil seal if required. I used three Allen head cap screws (M5-0.8 x 45 mm) on the stator, as they're easier to work with in limited space than the original Philips head screws.