Closed NOS Points with No electrical continuity

[svenedin]

I found an oil leak from the distributor drive tube. I removed the distributor to investigate where the leak was coming from (this is in a separate thread). I decided to fit another distributor that I have whilst I clean up the oily distributor.

With the alternative distributor fitted the car would not start (at all). This is a very good condition distributor, new old stock actually. I had fitted a new Distributor Doctor condenser, a new O-ring on the shaft, a few drops of oil with the rotor removed, tested the vacuum advance with a vacuum pump, cleaned the points with contact cleaner and set the correct points gap.

Using a test light connected between the low tension connection on the distributor and earth, I found the lamp would not go out no mater how I rotated the distributor in its clamp. I was very puzzled. I removed the distributor and checked that the condenser lead and low tension lead were properly installed with the plastic bush through their connectors and not short circuiting to the post. All was fine but still the car would not start at all.

I was getting tired and fed up so I took the distributor inside for further testing. I used my analogue multimeter to check resistance. To my great surprise, with the points closed and the meter probes directly on either side of the points contacts there was effectively no continuity at all (extremely high resistance which the meter read as infinite). I took the points apart. Brand new, never used NOS Lucas points but 50 years old. Clean but dull looking. I cleaned the dull layer off with 240 grit emery paper and tested again. Better but still quite a high resistance. I decided to fit new Remax points and immediately on testing the resistance is zero with the points closed.

Just an observation really. "Clean" points are not necessarily working points! It seems an oxide or other chemical layer builds up over time that is a very good insulator. So good in fact that electricity cannot flow through the closed points. Pretty obvious now why the car would not start but it was not obvious to me!

Stephen

[svenedin]

Up early and fitted the distributor having switched over the points to a new set. Car started immediately.

A very odd issue that I have never seen before. Seemingly perfect NOS points that are actually not working at all. Something so simple and basic that to bother to test it seems almost a silly thing to do.

I was also very puzzled by my test lamp being permanently on. I tested again with the new points (setting the static timing) and the test lamp behaved exactly as it should.

It does make me think about the posts where we hear, "my car won't start" and all manner of fiddling around and possibly wasting money on parts that were not needed when some basic tests would have shown an easily and cheaply fixed problem.

I can now carry out my test (to prove a point to myself) regarding the relative ease of starting the car with the starting handle with an electronic module (Pertronix, Hall effect) vs points (contact breaker). I could not start the car on the handle with the electronic ignition. My hypothesis is that the Hall effect sensor needs the distributor rotor to be moving quite fast in order to trigger a spark which is why it is so difficult to start the car with the starting handle. Points on the other hand will trigger a spark regardless of the speed of rotation. We shall see......I may be completely wrong on this and it is just my technique has deteriorated. Starting the car on the handle was a regular thing to do in my teens. People thought it was my party trick but really it was a knackered charging system and not enough power to use the electric starter!

Stephen

[myoldjalopy]

Well, it is true that the majority of 'my car won't start' problems are ignition problems.........

[svenedin]

I hesitate to say BMCEcosse’s favourite: it’s never the ….

[taupe]

From memory.... points used to come with a protective coating and the packs advised to carefully clean with a petrol soaked cloth before use?

i know I always clean them when servicing...

Taupe

[svenedin]

From memory.... points used to come with a protective coating and the packs advised to carefully clean with a petrol soaked cloth before use?

i know I always clean them when servicing...

Taupe

Yes you’re right. I thought switch cleaner (isopropyl alcohol) would do the trick but it did not. It's the same with the points on the SU fuel pump and the RB106 voltage regulator -advice is to clean the points before use and at intervals thereafter.

[svenedin]

Well the results of my silly experiment are in. It is easy to start my car on the starting handle with points fitted but I cannot start it on the handle with a Hall effect electronic ignition module (Petronix). Tests done on a warm engine. 4 successful starts in a row with points. With points it is still hard work to start a cold engine and rather tricky.

[myoldjalopy]

Another argument for retaining a good set of points then. The handle has come in handy a few times over the years when I have had the occasional flat battery.

[Chipper]

Sounds like you have inadvertently stumbled across a semiconductor, probably as you say, as a result of years of oxidisation having set in. Perhaps try building a crystal radio "cat's whisker" set with it...

[Sleeper]

and keep a small fold of fine emery cloth in your toolbox...

John ;-)

[oliver90owner]

and keep a small fold of fine emery cloth in your toolbox...

John ;-)

Avoid emery. I use a nail board, so a choice of coarse or fine grit.

[svenedin]

I have a little points file in my tool bag in the boot. Over many years the points in the distributor have never really given trouble unlike the points in the fuel pump. I eventually converted the fuel pump to electronic operation with a kit. Likewise I dispensed with points inside the RB106.

[myoldjalopy]

There is a school of thought that suggests the petrol pump points are self-cleaning, as they rub together in action. Maybe worth occasionally drawing a piece of card soaked in thinners through them as the engine bay is a dirty environment.

[svenedin]

There is a school of thought that suggests the petrol pump points are self-cleaning, as they rub together in action. Maybe worth occasionally drawing a piece of card soaked in thinners through them as the engine bay is a dirty environment.

Yes. They are said to have a “wiping” action that supposedly cleans them.