Model A Ford - distributor lower plate - avoid accidental grounding
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- Опубликовано: 27 ноя 2024
- 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.
Great stuff! So few, even the older, really knowledgeable guys, take the time to review the basic function of Henry’s distributor. As often happens, the stock parts are easier to troubleshoot and usually work best if in proper shape. Excellent content!
Thanks, I enjoy doing the deep dives. In particular, I like learning and teaching the proper names for components and subcomponents.
great video! thanks so much for posting this!
Shout out received. Thank you Alex! Well done.
Thanks, keep up the good work.
fantastic video! This is exactly what I'm dealing with right now and I had NO idea! Thanks for this great video!
I have used the modern lower plate along with a modern upper plate set up on a lot of distributor rebuilds for a while, but the lower plate I use is steel. I find that the modern condenser's I get with these plate set's aren't too reliable, so I install the modern brass tab contact for the lower plate part closest to the points and the modern condenser wire on the "outside" so the condenser can be changed without moving the brass contact tab. I know that di-electric grease is not a lubricant, but I smear some on the lower plate where the brass tab contact's it and never had a problem with lower plate wearing out.
I assume you mean the di-electric grease isn't *conductive* - it's a great lubricant. The problem I've always had with the "wireless" lower plates is that the brass tab pushes down on it, and after awhile the flange fatigues and only makes contact with the tab at its highest point. Glad it's working for you though. Maybe greasing the tab helps in some odd way.
Absolutely love ❤️ your videos and very informative many many thanks for the great information!!
Another great video. Thanks for posting this info.
I've put a piece of rubber hose behind the lower plate and dist housing. Silicone seal works also. I seen too many cables screw in too much.
I've heard of guys finding all sorts of stuff under the lower plate when they take apart old distributors, so it's clearly been a thing for a while.
If I ran it for a few times with both condensers would that have hurt anything?
Based on my understanding of how these work.... probably not? The condenser is a capacitor. Its job is to provide a ground path while the points are open and then feed that current back into the circuit to help the coil's magnetic field collapse. "When capacitors are connected in parallel, the total capacitance is the sum of the individual capacitors' capacitances. If two or more capacitors are connected in parallel, the overall effect is that of a single equivalent capacitor having the sum total of the plate areas of the individual capacitors." If the car ran fine with them both installed, I don't see how it could have hurt anything.