How often should ignition parts be replaced as a matter of course?

[Colin Lindsay]

I had one that went red hot on my Mk3 GT6 and boiled the oil out round the seams, but I never found why - I wonder if it was anything to do with the ballast system and the wrong coil? Almost 30 years ago now so can't check....

[Peter Truman]

Had one get very hot and fail on the Dolly Sprint appeared it had been leaking oil for a while!

[NonMember]

2 hours ago, Colin Lindsay said:

I had one that went red hot on my Mk3 GT6 and boiled the oil out round the seams

That used to happen on a moderately frequent basis when I first started working at Rover. We had a bench test setup with an early EFI coil (old-style wet coil like ours but low primary resistance) connected to an ECU with an In-Circuit Emulator in place of the processor. When debugging, it was common practice to set a breakpoint at an interesting point in the code, supply a crank signal and run to break. While looking at the back-trace and figuring out what had gone on, the engineer would forget that, having stopped the code mid-run, the automatic timeout of the coil driver no longer worked and the coil was still turned on. Twenty seconds of 100% dwell on a coil designed to be limited to about 10ms and 50% duty would overheat it to the point of producing a fountain of boiling oil from the vent hole.

[daverclasper]

Well, just fitted a NOS condenser and this one is sparking when points are opened. Possibly not quite as much, though still pretty visible.

Is it duff?

Cheers 

[Pete Lewis]

the size of spark is affected by how quick you open the points it needs a sharp snap not a woolly prod 

Pete

[NonMember]

21 minutes ago, daverclasper said:

Well, just fitted a NOS condenser and this one is sparking when points are opened.

To get HT out of the coil secondary, the coil primary current must drop off very quickly. However, doing so also generates a big flyback voltage on the primary, and if the points are opening slowly, the gap across them is tiny and very easily bridged by a spark. The condenser slows the drop of primary current but it's only intended to stretch the transition from instant to a few tens of microseconds. It also makes a tuned circuit that can oscillate, which helps prolong the spark. However, its main purpose is to protect the points by giving them at least some chance to open before being eroded by sparking (which also, of course, reduces wasted energy and allows more of the coil energy to go where you want it).

So I'm not surprised you see a little bit of sparking if you're opening them with, as Pete puts it, a wooly prod. As long as it's less sparking than you had before then I'd suggest the new condenser has improved things.

[Wagger]

You are correct in your descriptions and observations..

In old radios, the capacitors are the first components to fail especially the Electrolytics.

Most capacitors are made of two sheets of foil sandwiching a very thin insulating sheet made of some sort of plastic. Polyester, Polythene etc. This sandwich is then rolled up to form a cylinder. It only takes one pinhole in the insulation sheet to render the capacitor weak or useless. The one on our points has a very hard time, being charged and discharged thousands of times in a minute. They can also degrade in storage depending upon the conditions when they were made.

I used to service magnetisers that used 330uF 2000v electrolytics charged up to 800v DC.. They were connected to a coil via a large relay in order to magnetise a magnet in the centre of the coil. One pulse per second. Each capacitor lasted about a month. Usually, the connections to the terminals evaporated. Occasionally, they would short internally, boil the electrolyte and explode. They were contained in a strong enclosure. Very few manufacturers made any that would withstand this for more than a week.

1970's electronics was very entertaining. Almost as good as bonfire night.