auto advance Lucas distributor springs

[AustinWood]

The 2 springs are usually one light and one strong.
The light spring is fully extended as soon as the engine fires the strong spring then takes over.
This retards the spark for easier starting and it immediately goes on to the spring for the correct advance curve.
That's my theory anyway.
The Ducellier distributor in my Citroen SM is the same. One light, one strong and static timing is a little AFTER TDC.

[JonE]

My Lucas "one spring set" bag is 416042/S which somewhere (was it the Speedex site?) was listed for the Seven. They are both the same.

Do we categorically know whether the spec was two different (Lucas catalogue people??) or is that just what we find works now?

What is interesting is that, accepting the centrifugal movement in the Accuspark is likely what we are after, and with my pivot points being reasonably good in the Lucas unit, I cannot get the nice easy movement just by two fingers on the rotor arm top in any way shape or form. I'll try the Accuspark springs first...
These Lucas set original are however very similar, but tighter, than the springs which were on on the Lucas unit.

Has anyone got a new old stock unit that can photograph what appears?

[Chris KC]

Jon, flushed with success from uploading my 'engine won't start' troubleshooter yesterday, I will now attempt to upload a Lucas training course which I think you might find informative. See the section on advance mechanism.


  lucascourse3.pdf (Size: 2.17 MB / Downloads: 62)

The ideal of course would be to know what springs were fitted originally to the Seven distributor, but failing that, the advance curve which was aspired to.

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This might be of interest too :

"In the DK4A distributor, fitted with heavy “leaden” weights, the springs were relatively heavy items, provided as a matched pair, and which gave a more or less “straight line” progression from full retard to full advance as the speed of the engine increased, and until the total advance was checked by the stops in the action plate."

Source : http://www.da7c.co.uk/technical_torque_a...nce_di.htm

This article suggests there should be a linear increase in advance up to 1000rpm or so, at which point it maxes out (at +8 degrees).

[JonE]

Jon, flushed with success from uploading my 'engine won't start' troubleshooter yesterday, I will now attempt to upload a Lucas training course which I think you might find informative. See the section on advance mechanism.



The ideal of course would be to know what springs were fitted originally to the Seven distributor, but failing that, the advance curve which was aspired to.

---

This might be of interest too :

"In the DK4A distributor, fitted with heavy “leaden” weights, the springs were relatively heavy items, provided as a matched pair, and which gave a more or less “straight line” progression from full retard to full advance as the speed of the engine increased, and until the total advance was checked by the stops in the action plate."

Source : http://www.da7c.co.uk/technical_torque_a...nce_di.htm

I infer from this that your basic aim should be a steady (linear) increase in advance to +8 degrees at say 6000rpm.

oh my - how fabulous! It even has Distributor language so you can work out what DK4A means!
I spy with my little eye the DK also SEEMS to show differential spring weights in the image  - what do others think? That of course conflicts with the other information above, so perhaps some DK4A uses were a bit more advanced than Austin 7s?

[Chris KC]

I reckon he was right - a broad approximation is all you need for an A7.... in the absence of the correct machine I wonder if it would be feasible to run the distributor gradually up to 1000rpm and observe what the weights are doing?

[JonE]

ok, so who actually was Andy DeLuvian in reality, and is he still around?

I also note that Bruce White wrote about Austin 7 automatic advance curves and trials with a NOS Austin 7 distributor spring set. Is he still around?

[AustinWood]

I got some DK4 springs from The Distributor Doctor and they were one heavy and one light.
However, with the play in the old DK4 linkages the light spring did nothing so I changed to 2 heavy.
On my Citroen the light spring definitely works but the linkage is much better quality.

[JonE]

Jim - if you still have the other in a box, what resting length is it? And were the both the same length?

Here is the 1939 Lucas list for advance spring for DK4A, which goes to shoe why there are lots of erroneous ones around!
BN86 was 1937/39 Austin 7... can others identify the other Austin 7 models from here please?

I'd like to establish what are the right length original springs, which will at least be a first...!

  springs.jpg (Size: 77.18 KB / Downloads: 190)

[Ian Williams]

I would suggest that some of that information maybe misleading, dependant on engine spec we want to be at full advance somewhat higher than 1000 RPM, this figure will be distributor speed. I also disagree with Jim, sorry Jim, that the light spring should be fully extended at idle, but agree its influence is greatest at very low engine speed. My experience is that if you can eliminate play in the DK4 mechanism, which requires new parts or an ability to remake and or bush the old ones they work well, the most difficult problem to rectify was wear of the pins, fortunately new parts are now available, re-bushing the quadrant and body is also often necessary.

[JonE]

My ineffective springs are 21mm long overall, and they don't seem to operate until the 8 degree stops are reached. I note someone on the web has measured the "set of 5" Lucas springs (in this report, from Anglo Parts) which have been discussed elsewhere. They range from 16.1mm to 18.1mm in length.

https://www.custompistols.com/lucas-25d4...tions.html