123 Distributor

[arcturus]

FB george ben 3344 posted video

[142 Guy]

Originally Posted by arcturus

It's to do with the vacuum advance I believe.There should be a small connection nipple for the advance tube at three oclock on the body,to the right of the wires entry.The B20 123 is set up for vac advance

I am pretty sure that the 123 distributors use an electronic MAP sensor rather than a mechanical system with a vacuum servo (diaphragm) to control spark advance as a function of manifold pressure. Certainly all of the later ones that are user configurable for the spark map use a MAP sensor. If you have movement in the trigger wheel, its not because of the advance system.

[Nullifie]

The aluminium disk with the magnets has to fit tight on the shaft without any play otherwise the ignitions can't be at the right times. The rotor also has to fit tight, and is fitted on the top part of the aluminium disk, not on the shaft. Probably the inner hole of the aluminium disk and the fixing pen and the holes for this pen in the aluminium disk are worn. I had this once, see the picture: the pen is clearly worn at the ends, the holes in the aluminium disk for this pen can't be clearly seen, but aren't round anymore. This disc and pen are sold separately by the dutch 123ignition supplier, I paid € 50 plus shipping for them, the exchange is easily done.

[AidanC]

Originally Posted by Nullifie

The aluminium disk with the magnets has to fit tight on the shaft without any play otherwise the ignitions can't be at the right times. The rotor also has to fit tight, and is fitted on the top part of the aluminium disk, not on the shaft. Probably the inner hole of the aluminium disk and the fixing pen and the holes for this pen in the aluminium disk are worn. I had this once, see the picture: the pen is clearly worn at the ends, the holes in the aluminium disk for this pen can't be clearly seen, but aren't round anymore. This disc and pen are sold separately by the dutch 123ignition supplier, I paid € 50 plus shipping for them, the exchange is easily done.

Thanks for the info - is this issue a result of wear or just a faulty unit? If is wear, how much mileage was on the unit?

[Nullifie]

It is clearly a result of wear, probably the fit wasn't tight enough as it was new (so initial production fault) for with no original/new too loose fit no wear could result at this place; I don't know the mileage.

[Underdrive]

Nullifie, this is interesting thank you. It seems I am not alone and have reason to suspect the wear is causing some running issues. It's interesting that lots of owners of different classics fitted with 123's are claiming great reliability over high mileages. Perhaps early ones had some quality issues, don't know how old mine is.

[Underdrive]

Arcturus, I've sent you a PM on facebook.

[142 Guy]

Originally Posted by Underdrive

Nullifie, this is interesting thank you. It seems I am not alone and have reason to suspect the wear is causing some running issues. It's interesting that lots of owners of different classics fitted with 123's are claiming great reliability over high mileages. Perhaps early ones had some quality issues, don't know how old mine is.

Reliability is open to interpretation. In this case, the angular play in the attachment of the trigger disc is probably not enough to prevent operation of the distributor (until the pin shears completely and the disc stops rotating). The play in the trigger disc may result in ignition timing variability which may not be obvious unless you use an inductive pick up timing light to check the timing on an operating engine . Even with a timing light the variability in timing may not show up at idle and may only appear at higher RPMs or during rapid RPM transitions when the moment of inertia of the trigger disc causes it to slip on the shaft and change the timing. If wear in the locating pin is the source of the angular play I hazard the opinion that once the play has started, wear in the pin will only increase to the point that it will eventually fail.

If the angular play is only due to wear in the pin, I offer up the perhaps obvious alternative that replacing the pin (if you can source it locally) might be the low cost alternative to a 50 Euro fix. The other consideration is to attach the trigger disc to the distributor shaft using a retaining compound. I used Loctite 620 when I assembled my brass idler arm bushing on my 140's steering system. It is a high temperature product so good for the confines of the distributor; but, you need to heat it to > 300C for removal so no errors in the initial assembly please. A less aggressive adhesive such as a tiny dab of Loctite stud and bearing mount might do the trick just fine (and be much cheaper) in terms of preventing the disc moving relative to the distributor shaft and would facilitate future removal if you don't go overboard with the amount of adhesive.

[Nullifie]

If only the pin would have had wear, buying the disk would have been obsolete, but as I wrote, the holes for the pin in the disk and the inner hole of the disk fitting on the shaft also had wear, so only a new pin wasn't enough to fix the problem. Besides accelleration etc. the vibrations of the car/engine will let a worn disk be wobbling and this will result in a unstable ignition. Fixing the disk with adhesive will also be an solution, but then it will be hard to remove the disk if this would be needed to reach the electronic parts inside.

[142 Guy]

I missed your point about the holes no longer being round. That eliminates the 'just replace the pin' solution.