APPENDIX VII: Rebuilding a Lucas KNC1 Competition Magneto

I just rebuilt a Lucas Competition magneto that I'm told had been professionally restored less than 100 miles ago. As can be seen from the next photograph it looks great on the outside.


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Since the construction is pretty much the same as the Bosch ZEV, and since it wasn't such an internal disaster, I didn't take nearly as many photographs of the rebuild as I did of the Bosch. The next photograph shows it after disassembly:

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The important point is the earth brush on this magneto is hidden under the "Competition" tag, and it has to be removed before the armature can be pulled out of the housing. Next I pulled the bearing off the race at the end of the armature with the slip ring and then used a tool shown much earlier in this thread to extract the race using it and a two-jaw puller as shown in the next photograph.


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Next to the slip ring are the oil slinger, a few spacers, the race, and the bearing. A quick test with my Merc-O-Tronic tester already showed the coil was good so next the end cap has to be removed to gain access to the capacitor.


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No identifying markings are on the capacitor but it appears to be a 60 Hz line filter capacitor that magneto restorers often use, and which quickly self-destruct because they can't handle the high pulsed currents. I tried to test its capacitance but it was too heavily shorted to measure. At least the "professional restorer" hadn't slathered it with an excess of epoxy to make removing it time consuming.

I replaced the blown capacitor with a pair of Panasonics as on the Bosch ZEV, although attached to an adapter like shown in Appendix VI because it is required for a single-cylinder magneto. However, when I reassembled the armature I decided to use two screws from my stock that were in better condition than the ones I had removed from it. That turned out to be a mistake. As the next composite photograph shows the replacement screws were a few threads longer than the original ones so they protruded by ~1 mm..


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I didn't notice the problem until I tried to put the end cap on and there was a gap of ~1 mm. So, I switched back to the original screws.

After getting the right screws in it I reassembled the magneto and installed new points since the ones in it definitely had more than 100 miles on them. I then put it on my lathe using a bracket shown earlier in this thread. It sparked reliably down to 300 rpm (600 rpm engine) on the uncalibrated dial on the lathe. I then I magnetized it at 84,500 Amp-turns and redid the test. This time it was still sparking reliably down to the lowest speed on the dial of 250 rpm (500 rpm).

Since the speed dial on the lathe is only approximate, rather than putting the lathe in back gear to go slower I moved the magneto to my modified distributor tester. However, I haven't used it since moving to my new house ten months ago and I discovered that in the meantime the battery in the tachometer had died. So, once I get a new battery for it I'll see how low this properly remagnetized magneto will go and still continue to provide a reliable spark

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