Changing the Drive Head on 123 Electronic Ignition

I finally got fed up with the look of my 123 distributor and decided to do something about it. If you read my posts HERE, you'll know that - when fitted - the angle of the 123 distributor and cap was different to the old Ducellier and cap. It now pointed straight to the oil filler tower. 

Largely this was aesthetic but did cause some minor practical niggles. The solution seemed to be to to change the angle of the drive head on the bottom of the 123.

When the rotors of my Ducellier and the 123 were aligned side-by-side, I reckon there was about 15 to 20 degrees difference in head angle.

Difference in drive head angles - about 15 degrees?

I had considered drilling a new hole through the drive head.....

Difference in hole positions - Ducellier and 123 - about 45 degrees?

.......but the diameter that hole would need to be, meant that it would leave very little 'meat' on the head between old and new heads - possibly weakening the head.

I also considered a straight swap of heads between the Ducellier and the 123. Unfortunately the diameter of the shaft through the 123 is smaller than that of the shaft on the Ducellier.

Difference in internal diameter - Ducellier and 123

I could have fitted the Ducellier head just as it was and pinned it in place - but it would have been very wobbly and maybe prone to giving inconsistent timing or premature wear? or both? 

In the end I decided to shim the gap between the 123 shaft and the Ducellier drive head. The 123 shaft is about 10mm diameter and the Ducellier shaft is about 12.7mm, so i bought a short length of 12.7mm external diameter tube that is 1.2mm thick - meaning the internal diameter is just over 10mm. Luckily for me it fitted both parts a treat.

Ducellier drive head on a 123 shaft - plus shimming collar

I made the holes through my new shimming collar only as big as the pin that went through the head and the shaft. That way i didn't introduce any additional rotational free play.  in removing and refitting the drive head, i had to pay careful attention to ensure I refitted the head with the small and big halves of the head in the correct positions relative to the rotor arm. The beauty of this solution is that it's reversible - I can still swap back and use the 123 drive head if I want or need to.

I refitted it and went through the timing process again. Now the distributor cap points more towards the carburettor, but you can see that the catch for the distributor cap is clear of the water pump bolt. the HT lead between coil and cap is not stretched and the other HT leads seem more comfortable around the oil filler tower.

Old 123 distributor orientation

New 123 distributor orientation

What surprises me though - having re-used a foot from a Ducellier distributor - is that the 123 distributor isn't pointing to where the old Ducellier did. I think what this must mean, is that even though the difference in holes through the drive heads is, say, 45 degrees, there must also be a small difference in the angles of the holes through the distributor shafts of about 30 degrees...... The combination of the two (Ducellier Drive head on a 123 shaft) results in a net distributor position about 15 degrees more towards the carburettor than the original Ducellier position.

So - compared to that original Ducellier position - I can have my 123 pointing an extra 15 degrees in one direction OR about 15 degrees in the other direction...... but I can't easily have it pointing where the old Ducellier did. Changing drive heads alone is not good enough. Getting it *just* right means drilling a hole through a drive head, or through a shaft.....

On the 'plus' side though, the clip for the distributor cap is further away from the water pump stud.

I'm going to leave things be I think.