15-07-2022, 09:59 PM
Hello Ray
I know this thread has sort of finished, but I have been on holiday and couldn't log in to reply.
Reading from start to finish, I think your problem was/is high resistance in the contact breaker points. When things are working properly, the points carry about 4 amps whilst closed, and their resistance should be no more than 0.05 ohms so they will drop only 0.2 volts. This corresponds to a power of (4 x 0.2) = 0.8 watts. Since they are only closed for about 50% of the time, that makes an average power of 0.4 watts.
I can't imagine 0.4 watts (or even 0.8 watts if the engine is stopped with points closed) dissipated in a lump of metal like the points assembly being anywhere near enough to cause a large temperature rise, certainly not enough to burn fingers ! If they are really hot, either you have a short and they are carrying more than 4 amps, or their resistance is much higher than it should be.
High points resistance will of course cut down the coil primary current and weaken the spark. With the coil's king lead held near earthy metal and the points flicked, you should have enough voltage to jump a gap of 100 thou (i.e. much more than an ordinary spark plug gap) as the spark is only under atmospheric pressure.
I have often found that after a lay-up, the points acquire a high resistance film of tarnish and or white corrosion. For some reason, this only seems to kick in after you have driven for a couple of minutes. The tarnish/corrosion can be quite hard to remove fully. One effective method I have found is to draw very fine glasspaper between the points a few times, then flush out with switch cleaner aerosol. A final draw through with fine card soaked in switch cleaner completes the process. Without the switch cleaner flush, the insulating residue seems to stay sitting in the points gap and holds the two faces apart.
In theory, one should avoid emery paper as it leaves behind abrasive and electrically conductive particles.
In the car toolkit I keep a small fine grade "diamond spatula" which is easy to use and lasts indefinitely.
I know this thread has sort of finished, but I have been on holiday and couldn't log in to reply.
Reading from start to finish, I think your problem was/is high resistance in the contact breaker points. When things are working properly, the points carry about 4 amps whilst closed, and their resistance should be no more than 0.05 ohms so they will drop only 0.2 volts. This corresponds to a power of (4 x 0.2) = 0.8 watts. Since they are only closed for about 50% of the time, that makes an average power of 0.4 watts.
I can't imagine 0.4 watts (or even 0.8 watts if the engine is stopped with points closed) dissipated in a lump of metal like the points assembly being anywhere near enough to cause a large temperature rise, certainly not enough to burn fingers ! If they are really hot, either you have a short and they are carrying more than 4 amps, or their resistance is much higher than it should be.
High points resistance will of course cut down the coil primary current and weaken the spark. With the coil's king lead held near earthy metal and the points flicked, you should have enough voltage to jump a gap of 100 thou (i.e. much more than an ordinary spark plug gap) as the spark is only under atmospheric pressure.
I have often found that after a lay-up, the points acquire a high resistance film of tarnish and or white corrosion. For some reason, this only seems to kick in after you have driven for a couple of minutes. The tarnish/corrosion can be quite hard to remove fully. One effective method I have found is to draw very fine glasspaper between the points a few times, then flush out with switch cleaner aerosol. A final draw through with fine card soaked in switch cleaner completes the process. Without the switch cleaner flush, the insulating residue seems to stay sitting in the points gap and holds the two faces apart.
In theory, one should avoid emery paper as it leaves behind abrasive and electrically conductive particles.
In the car toolkit I keep a small fine grade "diamond spatula" which is easy to use and lasts indefinitely.