Brsitol 406: Advance spring LUCAS DX6A distributor

friend406 · #1 (**permalink**) 02-01-25, 08:43 AM

First of all my best wishes for the new year.

I have problem with 1 of the 2 advance springs of the pre-ignition from my Lucas distributor DX6 A of my Bristol 406.

This one has broken off and would like to replace it with 2 new ones. The Lucas distributor would be the Lucas type 40489A.

Who can help me with this?

flyinghorse1 · #2 (**permalink**) 02-01-25, 09:37 AM

I have recently got springs from here:
https://www.distributordoctor.com/

flyinghorse1 · #3 (**permalink**) 02-01-25, 09:39 AM

There should be a plate with more distributor details on the side as you will have to supply that information

David C · #4 (**permalink**) 02-01-25, 09:41 AM

If you were happy with how the car was running before the spring broke the least expensive solution would be to measure the diameter of the spring wire and try to find a replacement. I have a few used items that may be suitable.
There are specialists who will rebuild the distributor for you and supply springs and weights to get the advance curve back to something similar to the original. Ideally the distributor should be tested on a machine. I believe SLJ has or had one of these.
I have chosen to replace the distributors on my cars with new electronic units which can have the advance adjusted by a Bluetooth phone if you choose the Plus model. These include electronic ignition and have no weights to wear so give more accurate timing.
The units are made by 123 Ignition and cost much the same as a rebuild of a Lucas distributor. I believe the company is based in the Netherlands.
The distributors do not fit properly as purchased. They need about 3 or 4mm machined off the base to lower them and give more engagement with the drive dog. This is a fairly simple procedure that I have done on a small lathe without stripping the unit, just taping up to keep swarf out.

friend406 · #5 (**permalink**) 02-01-25, 10:48 AM

Hi David

thanks for the fast reply but what model of ignition 123 you put on your car?
What ingnition-curve you chose to be the good one?

Kind regards
Erik

JoeF · #6 (**permalink**) 02-01-25, 11:35 AM

I can also recommend https://www.distributordoctor.com/

A pair of springs is £ 21.60 including UK postage.

They use the distributor part number, so 40489A should be enough info.
(The actual Lucas spring set part number is 423347. ECM curve number 617.)

Attached is an old picture showing examples of the advance curves.

David C · #7 (**permalink**) 02-01-25, 11:39 AM

There are 2 models available, 123/Tune-6RVG which needs to be plugged into a computer to tune and 123/Tune+6RVG which has Bluetooth and can be programmed by phone.

I can't immediately remember which curve was used but we started with one of those programmed into the unit and it ran very well. In Racing supply the distributor modified to fit and will be able to suggest a suitable curve.

A subject for discussion is Vacuum advance. I asked In Racing about this and the initial response was that it's not necessary. I don't pretend to have any expertise but I do have basic understanding of the principle and I remain convinced that it should be beneficial for a road car if not for competition. Since it is included on the 123 distributor and simply needs programming I plan to enable it when funds permit a rolling road tune.

Geoff Dowdle pointed out to me that Lucas advance curves are quoted in Distributor degrees and Distributor revs .
These figures have to be doubled to correlate with engine RPM & Deg advance .