Daf 33 Points; Advice Sought.....

[andrew]

I've fitted dozens of sets of points over the years, both on Dafs and many other cars and I understand their function to act as a switch, opening and closing at a rapid rate, thus allowing the coil to charge and discharge, allowing the high voltage to jump the gap at the spark plug. So far so good.....

While I was at the Daf winter lunch a week or so ago, we helped get "Biddy", a Daf 44, running much more smoothly than she had been. In doing so, we discovered that the distributor was jammed in some way and was not permitting the vacuum or the bob-weights to advance the timing as it should. To effect a temporary repair, we fitted a Daf 33 distributor I had in the boot of my car, and fitted new points to it. We gapped and then timed the engine, using a strobe light and the results were plain to see; the car ran much better.

I brought the old points home with me and this morning I cleaned them up, using a fine stone. I then used a multi-meter to measure the resistance across the points.... And this is the curious part.... With the points open the resistance is infinite, as it should be, but with the points closed it starts with a low reading and progressively rises, much as it does when a capacitor or condenser is being tested. Should this be the case, and has anyone noticed this before? It seems that there's a"capacitance effect" within the points and I should have thought the reading would be zero, and stay at zero. My meter is a high quality one, and works perfectly.

Any ideas, anyone?

[gromsound]

nope no wizardry, it should just read immediately at zero ohms.
probably the anti spark capacitor is still fitted to the distributor?
or is there some later added radio anti parasite capacitor fitted?

[andrew]

Feb 16, 2020 14:51:12 GMT gromsound said:

nope no wizardry, it should just read immediately at zero ohms.
probably the anti spark capacitor is still fitted to the distributor?
or is there some later added radio anti parasite capacitor fitted?

No, the points are removed from the distributor and are currently on my kitchen table! I have another set of Daf 33 points in a box, so will check these first before going further.

(Half an hour later;) I've just opened a packet of new points and tested them in the same way. They show zero resistance when touching, so I have decided that the earlier ones are defective in some way. Aside from the distributor playing up, a dodgy set of points wouldn't have exactly helped Biddy move about either! It's a learning curve with these Dafs!

[starider]

Hi, I am in NO WAY an authority on electrics/electronics, but should the contact area of each part of the contact breaker set be virtually flat so that when together there is a large area of contact to give a high reading?to repeat I am no expert what so ever,so am interested to find out the result/reason..............starider

[bobdisk]

The points should both have a flat surface, and positioned so that the whole surface of both points contact each other when closed. This will make the lowest resistance. When the moving contact is pushed open by the distributor's cam, there will be an infinate resistance, ie open circuit. There is a hardened piece of metal that is the contact on the ends of each of the points, that does the contacting. If that is not tight on either the spring of the moving contact, or the fixed contact, there can be a resistance at the point where it is fixed. If it was like that when new, there would have been arcing and that will create a resistance. Andrew, if you waggle that where the parts join, I bet one or other will move. This would have been happening in operation, and be the cause of the rough running.

[andrew]

Given that I had condemned this points set to a metallic grave, I thought I'd have one last attempt to have them working before I gave up on them. To this end I dismantled them and used a whetstone to put a "shine" on both the contact surfaces. Upon reassembly, the results were perfect! No resistance whatsoever on contact and there was no reoccurrence of the increasing resistance, no matter how long the multimeter remained connected! I now have a perfectly useable set of points, when I need them. I love "tinkering" with things and do dislike trowing them away.