DK4A distributors

[Howard Wright]

Hi All

I’ve run the Brookfields on a DJ4 manual advance distributor since I first put it together.  I thought I’d try an automatic advance DK4A. This is partly due to the increased tendency for the engine to knock using E10 fuel.

I have three DK4A distributors, two I believe are A7 originals and one from somewhere else. Top left in the photo is BN 86 838 8, top right is BN24 756 and what I believe is non Austin is the lower one marked BN30 435.

Both the distributors in the top of the picture have fairly sharp cam lobes whereas the lower one has more rounded lobes.  The top two show an arrow indicating anti-clockwise from below there is no arrow on the lower one but the Bob weights are in the same orientation as the other two.

Could anyone please indicate which are suitable A7 distributors and what effect the sharp cams v rounded cams would have on performance?

Cheers

Howard

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[JonE]

the important numbers are top right... can you quote those?
BN24 is probably 8HP Austin from 1940s.

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404225 is from a Riley 1.5.. but may have read the digits on the lower one wrong as that is a CHA rather than a BN.

[Howard Wright]

Hi Jon

Top left 405508

Top Right 402248

Bottom 404281

Thanks

Howard

[Bob Culver]

Even with the correct numbers and the correct advance range, the springs can by now be anything.I would certtinly retain the manual control as an override.

[dickie65]

If the spindle rocks about above the bob weights or below you will have a lot of spark scatter and the points gap will never be consistent.
The later Dizzy has to be in excellent condition to be any better than a manual advance one.
Which are capable of running up to 6000 + Rpm before points bounce becomes an issue.
If the engine is knocking you are probably running with too much advance or possibly labouring the engine.

[Howard Wright]

Thanks Dickie

The main issue has been the need to alter the timing almost constantly. 

I can judge when the ignition is advanced or retarded by the sound and engine response but recently and using E10 fuel the manual timing needs almost constant attention and the novelty of playing with the steering wheel lever soon wares off!

I’ve fitted one of the distributors (top right photographed above) today and a short 10 mile drive has been much more pleasurable.  All three of the distributors in the photo are not particularly worn and the one fitted seems very useable.

Cheers

Howard

[JonE]

haven't got any of those numbers on the database I've accessed in the past, sorry.

[Bob Culver]

The two advance curves are very basic and to emulate with manual control requires very little attention after starting. Just a slight retard when flat out under about 30mph in top.
What are orther's experience?
When very hot engines will ping momentarily and run on after the overrun when oil is pumped into cyls and not initially burned.
not observed today as moderns burn no oil.
It can be of interest to calibrate the hand control.

[dickie65]

Valid point on the E10.
I never use the stuff as my engine is a bit modified hence it will pull 6000 rpm in third.
I find that I do not have to fiddle with the timing much at all. I just retard for starting then set it for fastest tickover when warm and only advance it again at around 3000 rpm and again at 5000 rpm.
When I drive it in anger I just run it at a fixed advance for about 4000 rpm ( Hillclimbs and Sprints ) I use about 3500 rpm at the start line.
For road driving I find its not too fussy.
I hope to demonstrate it at the centenery Prescott Event.
Here is an example of my Sunday driving

https://www.youtube.com/watch?v=alFAAk2Fv74

[Howard Wright]

Hi Dickie

Impressive video.  

The main reason I use E10 is that I’m finding E5 difficult to get.  The last few visits to my local Tesco have had it sold out.  I have a Ricardo head, four branch and 1 1/4 SU so mildly tuned and I probably need more effort to find E10.

Cheers

Howard