distributor timing

[steve62008]

had to replace the snap clips on the distributor on my Pearl.  Low and behold, it was not secure and rotated rather freely (actually helped at the time as it made pins holding the clips more accessible).  Now I have no idea where the timing should be.  I know you can fine tune it, but need to get relatively close or the car won't start and I don't have the patience for trial and error.  Anyone know where it should be set (i.e. where the pointer should point)?

Should have looked before I started, but then I would be a whole other person, yeah?  Plus it moved so freely, no guarantee it was even close before I started messing with it.

Thanks in advance,
Steve

[Reckless Rat]

Assuming you've got a Lucas DK distributor with auto advance, set n°1 piston at Top Dead Centre using the marks on the flywheel and checking with the plug removed that its on compression stroke. The rotor arm should be pointing at n°1 lead on the cap and the points just opening. The engine should start. You might have to fine tune from there but once its ok lock everything off on the base plate.

[Malcolm Parker]

It might be easier to take the spark plugs out so the engine turns easily on the starting handle, then put your thumb over the no. 1 cylinder spark plug hole,  turn the engine over on the handle, you will feel when no. I piston is at the top of its stroke.  Do it a couple of times if necessary.  If the plug is over the piston, you can pop a bit of dowel or a ball point pen or similar down the hole and see how it goes up and down as you turn the engine over.  Once the piston is at the top of the cylinder on its compression stroke, set the rotor arm in the distributor at no. I plug lead terminal.  Replace plugs and distributor cap and all being well it should start up.  Once running, turn the distributor anticlockwise slightly and it will affect the running.  If the engine starts to sound rough, turn the distributor clockwise (ie retard the timing)  Too much and the engine will sound dull, so turn it anticlockwise again and the tickover will increase, I like to set it so the engine is idling quite fast without sounding rough.  Clamp the distributor and try the car on the road.  The engine is very sensitive to timing, so only make minor adjustments.

[Hedd_Jones]

sounds like you havnt taken the dizzy out of the dynamo?.

If so your timing is very close as is. Turn it clockwise as far as it will go. turn ir anticlockwise as far as it will go.

Put it in the middle and see if it will start. I bet it will. If not then try 1/4 of the total adjustment each way.

There isnt a single setting that works. So trial and error is king. Ignitio timing is dependant on all sorts of variables.

[Bob Culver]

This topic has been exhaustively covered before but it is easier to redo from scratch.
Those very familiar with Sevens can adjust by ear. It is vital that no more advance than necessary is applied as crank stresses rise very significantly with advance. An engine with generous advance sounds stroppy and has a sharp exhaust but may not be better. Don’t judge by stroppy sound.
The following applies to normal Sevens driven as intended to about 3,500 rpm (30 in 3rd/2nd). Not the high revving sports and racers. The original handbooks for manual advance cars suggested 1 ¼ to 2 inch (14 to 22 deg) full advance on the crank as an initial setting. Most will run merrily with considerably less than 2 inches (the Williams book adopts only 1 7/8 for specials.). An ongoing source of confusion is that the early Ruby book and many others repeated the manual recommendation. But when hand cranking the auto advance ignition is retarded not fully advanced. This has led to myriad problems over the decades and a lot of unnecessary crank stress. To further complicate matters there are two original auto advance distributors. Whatever the markings on the body just what springs and innards are fitted and the degree of wear and effect is often a puzzle. The eary Ruby distributor with 3 dist/6 crank  deg  of advance should be set about 7/8” btdc on crank or a bit more and the later 8/16 deg Ruby distributor, at tdc or somewhat more.
In general, as distributors wear, advance increases. If you can find a suitable long screw to fit down the middle advance can be twisted to full advance and locked in place with a washer. Can then find where full advance takes you.
15 deg btdc is piston 1/16 from top of stroke, on later heads can be found with a vernier depth gauge etc. 

[John Mason]

Hi Bob, On reading your comments on Ruby's and the two types of auto advance distributors. Is there any way of identifying which distributor you have fitted to your car. My car is a March 1935 Ruby but there is know way of telling if during its lifetime the distributor has been changed.

John Mason

[Chris KC]

There can be few original DK4A distributors still running as they were when Austin fitted them. If you are reluctant to strip the unit, set up a DTI on one side of the rotor arm and twist the distributor shaft by hand against the advance springs, it's then a fairly easy task to figure out what the max advance angle is from the measured deflection. The rate (and slop) of the advance springs is quite another matter, and can only be meaningfully assessed by using a strobe light and rev counter while the engine is running to plot the advance curve. Timing on A7's is not particularly critical and in any case the ideal amount varies from car to car (with compression ratio, for example) so you may have to content yourself with a 'ball park' figure that goes alright on the road. As others have said, too much advance is the main thing to avoid.

[Ian Williams]

The other thing not mentioned and which makes quite a difference is the fuels available then and today, pre war pump fuels will have burnt at a different rate to modern fuels. Therefore notwithstanding wear and other variables old recommendations should only be considered a rough guide, this is also true for carb settings as specific gravity's of fuels have changed. On any seven TDC fully retarded will get the engine running, as others have said fine tune from there.

[Bob Culver]

Hi John
The advance in distributor degrees is marked on the label. But, as KC, actual full advance from the hand cranking advance can with substiute parts and wear now be anything.
(When dismantling distributors in place for a look see, easy to replace the rotor assembly 180 deg out! Can be a very elusive fault.....)

[Bob Culver]

There is much to be said for manual advance. With Sevens the acceleration allows ample time for any adjustment!
For those curious it is not difficult to rig a temporary manual override using the throttle control cable assembly from an old lawnmower etc. As most pulling  is done in the 2000 to 3500 rev range, once under reasonable way the range of adjustment required is very small , only 2 to maybe 5 crank degrees.