Custom Coil-On-Plug Ignition Conversion, Page 1
This project began with me being tired of spending exorbitant amounts of money on new ignition wires every couple years. I began to investigate the idea of converting to coil-on-plug (COP) ignition to clean up the engine bay and avoid buying overpriced wires. Aside from that, the COP design seemed inherently more reliable. So, here we go on the wild ride! My first idea was to use the original M42 coil packs. I disassembled some spares just to get the hang of what I could and couldn't do. Beyond that, I needed to get some basic dimensions worked out to choose ignition boots.
Once I had the ignition boots in-hand, I could make some more progress. From the measurements, I determined that the boots were not long enough to make enough contact with the spark plugs (at least not enough to leave me feeling confident about it). Using a multimeter, I could see that contact was being made, but it was very light and I feared that normal engine vibrations could cause interruptions in the contact. I addressed this issue a little bit later. The spark plug bosses were measured to be ~9mm tall, so I would mill them down roughly 7mm.
So, with that worked out, I began making the necessary modifications to the coil packs. They would not fit in the valve cover with the four mounting tabs still on them, so I lopped them off and re-welded the exposed cuts. I did this both to keep them from falling apart, and to ensure that as much conductivity was preserved as possible, since these ferrous slats were an integral part of the primary field generation apparatus. Among the pictures taken that evening were some of myself (hiding in the welding mask) and my father playing with his mill.
Next up was test-fitting the coils in the valve cover and modifying the plug-hole bosses. The operation took a few light passes, just to ensure that nothing got mangled. Having access to a mill is a big help with things like this...a hand-file would not have been much fun. A Dremel tool would have resulted in all sorts of things getting scratched up as well...holding one still is a real chore!