Ignition advance measurement

[Peter Naulls]

Can anyone tell me a figure for the maximum advance, measured at the rotor arm, for a DK4A distributor? That is the rotation between rest position and full movement of the bobble weights. I'm sure I have a figure somewhere in a manual but I can't find it ...

Peter.

[Chris KC]

Hi Peter, as standard it's 8 degrees (3 degrees on early ones) i.e. 16 (or 6) degrees at the flywheel.
For an Austin Seven DK4A, that is - there are many other variants and many of those have found their way onto Sevens.

You may find it stamped on the little scale attached to the side of the distributor body if it is still there; or on the underside of the 'action plate'. More than likely said plate has worn a little and the advance has correspondingly increased.

[AustinWood]

It's stamped on the plate inside the distributor to which the weights attach that cause the advance.
There is a pin in a hole that limits the advance. The hole is larger than the pin and that is what sets the maximum advance. Bigger hole - more advance. The hole is usually very worn so the advance is more than the original design.
On DK4s I've usually found everything about the advance mechanism is very worn. Frequently it may not advance at all or else fly to maximum advance straight away.

[Bob Culver]

When hand cranked the rubbing contact tends to drag the rotor to full retard, but if the motor is run and a new fangled light used, some intermediate advance usually occurs however slow the idle.

Although it does not totally gaurantee the working full advance position, the rotor can be twisted and locked with a long screw down the centre and washer. This enables the likely max advance on flywheel to be determined, usually the key vital setting as it applies for most running (unless some non standard stiff more progressive springs have been substituted).

For the benefit of newcomers, it is important that the least advance for acceptable actual performance (as distinct from noise) is used, especially with original cranks.

Assuming the distributor innards behave as the label, the appropriate very different static setting applies. The early Ruby handbook, and copiers of, very inappropriately repeats the advice intended for manual advance cars.

[Peter Naulls]

Thank you all for your replies.

My very crude measurements suggest it is somewhere around 15 degrees on a reconditioned unit! The holes which are prone to wear show virtually no wear - but are bigger than those on various old distributors I have. I suspect that in the process of "reconditioning" the engineer has drilled out the holes to conceal the wear.

Has anyone tried bushing the holes or welding them up to restore to the correct advance?

Peter.

[Chris KC]

Yes - the way I approached it was a dab of weld on the worn side of the hole and a bit of deft work with grinder/ files to restore it to flatness and the correct amount of advance (which I confirmed initially using a DTI against the side of the rotor arm).

You'll need to dismantle the unit to do this properly I think.

It's just as likely Peter that it's a plate from a different variant - there were hundreds of DK4's with different settings and most of the bits are interchangeable.

On a sporting engine you might get away with, say, 10 deg at distributor, but in my book 15 is too much and will put your crank under definite strain.

[Peter Naulls]

Thank you Chris, very helpful; the interchangeable parts scenario sounds like a likely cause.
I will weld and fettle with confidence!

Peter.

[Chris KC]

By the way the reason I welded from one side was so as not to lose the positioning of the hole - it's probably a good idea to make a few reference marks just in case. The precise hole size finally was mostly trial and error, it doesn't quite work out the way I tried to calculate it.

[Ian Williams]

The base plate hole size's of the variants are as follows:
4 deg 1/4" diameter
8 deg 21/64" diameter
10 deg 3/8 diameter
Which one you need and the weight of the springs will be governed by the state of tune of our engine.

[Peter Naulls]

Thank you again, most helpful Ian.

Peter.