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I am overhauling a DK4 automatic advance distributor. It seems to be in fair condition, apart from a cracked cap and worn serviceable parts. It has an 8 degree advance plate, but I understand that the version fitted to the higher compression engines has a 12 degree advance. As my engine has the later higher compression Ruby head, I assume that 12 degrees is more appropriate. Does anyone know how I can modify the base plate to give the extra advance? I assume that the holes need to be enlarged, but does anyone know by how much?
Regards,
Jamie.
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Location: Scottish Borders
Most of the ones I've seen have considerable wear to the holes that limit advance. They probably advance more than the number stamped on the plate.
Jim
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post a pic of your holes?
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My own experience of modifying the advance plate is that you will do better to proceed slowly/ incrementally and measure the result (use a DTI). It's not quite as 'linear' as one might suppose. As Austin says, many plates need reducing rather than increasing, once stripped the hole is 'restored' with a blob of weld and filed back to the desired size (flattening off the blob, of course).
Beware too much ignition advance, it has seen off many a tired crankshaft.
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I'm no historian but I must concur I thought 8 deg rather than 12.
These are distributor degrees of course not flywheel degrees - 24 deg of advance at the flywheel puts you up there with the racing boys - maybe OK if you have a new crank and rods, not sure I'd chance it on originals.
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Jamie,
I had problems with the timing over-advancing on my 37 Ruby; when set to give a reasonable pick-up at low revs it sounded quite rough at higher revs. I took the distributor off, clamped it in the vice and made up a couple of plasticard discs, one to screw to the distributor body, and another to slip tightly over the shaft where the rotor arm normally fits. Having marked one of these in degrees I was able to accurately measure what was happening. I found it to be advancing by about 12 to 13 degrees even though the holes looked only slightly worn.
I welded up the holes in the base plate as Chris described, then gradually opened them up with a round file until I had my preferred 7 degrees. You can do them one weight at a time to make sure they both "stop" at the same advance.
It made a big difference to the running of the car. Well worth the time spent.
Peter.
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Location: Malvern, Victoria, Australia
20-08-2020, 03:35 AM
(This post was last modified: 20-08-2020, 03:40 AM by Tony Press.)
Not seen this before but the Cornwall Club Technical Articles, Distributor Maintenance does show:
"2. Lucas Automatic advance
From the Ruby onwards, a driver aid was fitted that did away for the necessity of adjusting the timing by hand to start the car. The Lucas DK4A series have an automatic mechanism that also varies the timing a little bit, some 8 degrees, in relation to the engine speed. As compression ratios were increased and fuels improved, the later cars’ mechanism allowed more advance at 12 degrees. This gives a little bit more power at high revs and a little bit smoother tick-over when combined with the higher compression engines.
This article, written by Geoff Hardman and Andrew Jarmin, originally appeared in CA7C Seven Focus in July 2009 pp22-24, and Aug 2009 pp23-26."
I don't think this is quite correct !
Their Data page states Lucas Auto advance early 3 degrees later 8 degree !!
