Distributor Advance Springs

[Graham Barker]

On my DK4 1937 distributor, one of the springs is stretched and therefore  not pulling the weight back to the at-rest position - please see photo. Do you think I should replace that spring with an unstretched one or could there have been a need to create that stretch in the spring?    

[Peter Naulls]

This might be a red herring but I have seen more than one dizzy with unequal strength springs. Perhaps someone has been stretching this one to crudely alter the advance curve... that doesn't answer your question though.

[A G Wood]

A discussion on DK4 springs here:

https://www.austinsevenfriends.co.uk/for...p?tid=1353

[Graham Barker]

Thanks for pointing me to that thread. I learned a lot from it, particularly from the Lucas distributor training course that was referenced in one post.
The information makes me think that I have two of the heavy type of spring, whereas the Lucas diagram shows one heavy and one light spring. My hunch is that the original light spring was broken or lost and that a new light spring could not be obtained. Consequently a heavy spring was stretched then fitted to allow some free movement at low revs.
As the car is a standard Ruby, I don't think that the fitting of a stretched spring was a well thought-out performance enhancing trial that might have been attempted on a racing car.
So I guess I should be looking to find and fit a light spring.

[John Cornforth]

Hi

I have dug out an old article by "Andy DeLuvian" (I believe a pen name of Barry Riseley) which appeared in the Austin Seven owners club magazine some considerable time ago. To summarise, for 1937 to 1939 the distributor is a type DK4A with Service Number 405508, later replacements were Service Number 40224/S. In both cases the advance springs set was listed as Service Number 405396/S. In another part of the article it is claimed that both springs were the same.

The advance curve is:

0 deg below 250 RPM
3.5 to 4.5 deg at 1000 RPM
6 to 7.5 deg at 1400 RPM
7 to 8.5 deg at 1800 RPM

By Lucas convention, these are all RPM and degrees at the distributor. At the crankshaft this becomes

0 deg below 500 RPM
7 to 9 deg at 2000 RPM
12 to 15 deg at 2800 RPM
14 to 17 deg at 3600 RPM

Which is not far off a simple straight line, maxing out at about 3100 RPM. To these figures you have to add in the static advance, maybe another 8 crank degrees.

The DK4A model was of course used for other cars, and would have had a different service number and different springs so there are plenty of variants "out there".

All a bit academic really, as fuel has changed, engines are sometimes tuned and advance (within limits) isn't that critical once running.

[A G Wood]

Graham, this is the spring listing from the '39 Lucas Parts Catalogue (apologies-if the file doesn't auto open you may have to 'open with...' it)
If you are going on a spring hunt, it may be of use?
I see you are located in NZ, Quality Rebuilds might have some NOS springs, although I see Wayne has recently sold the business to Carburettor Restorations.
Regards
A G W

[John Cornforth]

Hi

Thanks to AGW for that listing

I am interested that the column heading says Pair (or Set), the implication being that a Pair was two the same and a Set was two of different types.

It's a guess, but does /S at the end indicate a Set ?

If so, the 405396/S which I noted above would be a Set.

[A G Wood]

And here's the rest of the spring sets  which look to be for 6 & 8 cylinder distributors fwiw.
And bonus weights
I'm not familiar enough with the minor details of Lucas distributors John, to be able to hazard an opinion but I would say what you deduce makes sense, perhaps someone has an un-molested sample to confirm or deny?

[Graham Barker]

Many thanks to those giving replies to my thread.  I have learnt a lot, but still don't have a definitive answer on whether to have two heavy springs or one light and one heavy.
As suggested in one of the posts, it would be great if some owners of standard high compression engines, who believe that their distributors have unmolested springs, would share their setup with us.
Regards 
Graham.

---

Hi AGW, I will phone Quality Rebuilds and ask if they can shed light on the matter. 
Regards 
Graham.

[JonE]

In the FB Austin Seven group, there is post with a bit of film on 18 July on my new old stock unit and the bounceback of the advance weights. I think both springs are the same. It isnt as loose as an accuspark unit, but feels snappy. And snaps, audibly.
I just can't understand why we haven't as a group come up with some spring re-manufacture project rather than rely on the NOS pieces in the Distributor Doc collection? They must exist as equivalent manufactured items somewhere, and once we'd identified them, they would be pence to have a few thousand en masse. Has some in-magazine research been done perhaps; like the comment about using Minor springs? I'm happy to use this unit to test some others in.