This video gives some tips for avoiding a short circuit when using a stock distributor lower plate - particularly when using a stock lower plate and a "modern points" upper plate.
Some background on condensers that I couldn't fit into the video:
Remember that a condenser is a capacitor. It acts like a spring, absorbing and then releasing electricity. When the points open, the current coming in through the primary ignition circuit loses its path to ground, and it starts searching for a new path to ground. The condenser absorbs that electricity until the voltage pressure pushing out of the condenser exceeds the voltage pressure coming into the condenser from the primary winding. This all happens in a few microseconds. When the balance flips, the condenser releases its stored electricity back along the ignition circuit, through the ignition switch, and into the coil. This helps to collapse the coil’s magnetic field and fire the spark plugs.
That’s why the condenser used to be connected directly to the bus bar. But a problem developed - that location exposes the condenser to a lot of heat. The exhaust manifold is literally a few inches away. The heat coming off the manifold conducts into the distributor body and right into the condenser. The condensers made back in the ‘30s and ‘40s couldn’t handle that kind of heat very long. They basically cook; the wax paper insulating layers degrade and they short out. So over time, the condenser got moved - first to the outside of the distributor, and then by 1949 the condensers got smaller and they were moved up near the points.
Since the ‘50s, Model As have often been retrofitted with these “modern” upper plates to keep the condenser working longer. However, in the mid-80s, A&L Parts started producing condensers using polyester insulation that could take the heat in the original location. So now the situation has basically flipped, and if you’re building a Model A nowadays, you’re better off using the stock points and stock condenser.
Having said that, a lot of folks, myself included, are still using the ‘50s-era points, and most of the time they work fine. Setting the points gap is a little tricky, because two screws have to be adjusted simultaneously, but you manage.
Quick update: I've learned that Snyder's is now selling a wireless lower plate that resolves a few of the problems I noted with the plate in the video. I still think the wireless arrangement is inherently faulty.
7 мар 2021
