Setting Ignition Timing On Cars Manufactured After June 1971

On an internet forum there has been a very long and protracted discussion about helping a fellow DS owner trouble shoot problems setting up the timing on his car. He happened to be fitting 123 electronic ignition, but the big debate wasn't really 123 specific. It concerned the underlying instructions for 'pre-setting the static timing' on Ds manufactured after July 1971.

In Citroen's 'manual 814' and it's French equivalent 583, the instructions for setting the timing are essentially these:

• Use the notch in the flywheel to find the static timing position
• Mark this as 'position zero' on your timing gauge.
• Set the distributor up to cause an ignition spark at that point
• Run the engine
• Set/ adjust ignition advance (move the ignition point) for the particular engine.

In essence, Citroen provide these same instructions for cars built before July 1971 and for cars built after July 1971. What's the significance of that date? 

• For Ds built before July 1971, the notch in the flywheel  - used to pre-set the static timing - gave 12 degrees before top dead centre for number one cylinder - 12BTDC. This is established and proven to be an adequate static timing point for completing the rest of the timing set-up process
• After July 1971 the piston of the notch was moved. it now gave top dead centre for number one cylinder - TDC. 

Notch in the flywheel

Regardless, the Citroen instructions for ignition timing are essentially the same. 

Citroen timing instructions for pre-July 1971 engines and.......

......Citroen timing instructions for post-July 1971 engines.

In both cases the instruction is to use the point given by the flywheel notch, as the point at which to set up the initial distributor ignition - the static timing.

The upshot of this is that for post July 1971 cars, because you start at TDC, when you set the static timing, initial spark ignition would take place slightly later - when the engine was at TDC. And combustion would occur when the piston was well into its down stroke. And when setting the advance, you would expect to need to move the distributor and ignition point more (degrees) to reach the same ultimate timing position than you would for pre July 1971 cars.

Well that's theory.....even though the intended process of setting the advance would ultimately leave the engine with the correct degree of timing, the problem and debate on the forum concerned practice: whether or not beginning the process at TDC is a viable start point. The recent debate on the forum concerned the wisdom of running an engine with ignition happening this late, whether it might cause engine damage and whether the engine would run at all. If you can't get the engine going, you can't set the advance......

The general consensus was that - for Ds built after July 1971 - following the Citroen workshop manual and starting the timing setting process from a 'static timing position' of TDC was simply not viable. Citroen were lambasted, and  - for the DS owner being helped - the 123 manufacturers were pilloried for not correcting Citroen's mistake.

Worried and confused? So how can you tell what flywheel is in your car? How do you set the timing on a DS manufactured after July 1971?

Worried

Don't be.

Confused

Read on.

Does Your Flywheel Notch Give 12 degrees TDC?

If you are not sure what flywheel your car has - or simply want to check - you can go about it this way:

• Remove the spark plugs and slowly crank the engine (or if a five speed, jack up a front wheel and turn that).
• Identify the beginning of the compression stroke of number 1 piston using a balloon or similar.

Balloon deflated - engine not at compression stroke

Party time! Compression stroke found!

• Stop just as the balloon begins to inflate. Remove the balloon and slip a long dowel or screwdriver into cylinder number 1 as a 'tell'.

Using a marked dowel as a 'tell' to find TDC
(The white cap is only there to centre the dowel)

• Insert a 6mm pin (a drill bit is ideal) into the timing hole under the alternator.
• Continue to slowly turn the engine until the drill drops into the notch in the flywheel and 'locks' the engine. (You should also have noticed the dowel/ screwdriver rising as the piston continues up on its compression stroke - until the point the flywheel locked.)
• REMOVE THE DRILL.
• This is the crucial bit: continue to turn the engine slowly and, at the same time, observe the dowel/ screwdriver sticking out of the top of cylinder one.

Case 1: If the dowel/ screwdriver continues to rise for a while before beginning to descend, then the point at which the drill engaged with the flywheel was BEFORE top dead centre (aka 'TDC'). For carburettor DS cars built before July/ August 1971, the expectation is that you will find 'case 1'. On these cars the point at which the drill drops into the hole beneath the alternator (the timing point) gives 12 degrees before top dead centre (the firing point). The timing point and the firing point are the same.

For this 'case 1' scenario, I covered the process for setting up the static timing with a mechanical distributor HERE and HERE, and for fitting a 123 electronic distributor - including setting the advance - HERE.

Case 2: If the dowel/ screwdriver immediately begins to descend, then the piston is also descending and the point at which the drill engaged with the flywheel was already AT top dead centre. 

From July/ August 1971 onwards, the expectation is that you will find your car/ engine meets 'case 2' above. On these cars the point at which the drill drops into the hole beneath the alternator (the timing point) gives zero degrees before top dead centre - TDC. So how do you set the timing??

How To Set The Ignition Timing Where the Static Timing Position Gives TDC

The general consensus was that a static timing position of TDC cannot be used to set the static timing. The position of the crank and piston needed to be altered before the static timing could be set. In essence a slightly earlier static timing point needed to be found and used. Some people say the engine needs to be "wound back" but in reality this means "winding it forward" again.

This would seem to be a good way to go about things......

• As above, find the intended statistic timing position using a 6mm pin. This needs to be using number one cylinder and when the piston is on its compression stroke.
• Slowly rotate the engine to cause the 6mm pin to drop into the timing slot of the flywheel. (For these engines/ flywheels this is of course TDC).
• Put a thin white mark on the flywheel opposite the 'zero' of your timing gauge.

White mark opposite the zero

• REMOVE THE 6MM PIN
• Rotate the engine again until you again find the start of the compression stroke for number one cylinder again. 
• Now slowly continue to rotate the engine until the temporary mark you made is opposite the '6'  mark on the gauge.

You might find the engine over-rotates and your mark goes past the '6'. if so, repeat the exercise  until you successfully stop the mark opposite the '6'. 

• Without disturbing the engine any further, set up your distributor to cause ignition to happen at this point.

For an  old mechanical dizzy, this is the process of using a test lamp to indicate and so set the precise point at which the contact breakers open.

And if you are fitting 123 ignition, this is the point at which the little green LED light comes on.

• having found this point, clamp the distributor up just so that it can only be turned stiffly.

What have you just done? Even though the notch in your flywheel finds the TDC point, and your white mark on the pulley indicates TDC, you have set your 'static timing position' when the engine was 12 (crankshaft) degrees before TDC. As such, you have mimicked the process for cars manufactured before July 1971 and should be confident that the engine will run sufficiently for you to complete the timing process - setting the advance.

Setting The Engine Advance

If you have followed the steps above, the key point to bear in mind here is that while you have set up your distributor to trigger ignition at 12 degrees before TDC, the mark you have made on your pulley equates to zero degrees of advance. So when setting the advance, you need to see the full amount of advance on your timing gauge. You don't need to do any column 'C' maths to account for the 12 degrees as would otherwise have to do for a pre July 1971 car. Follow column 'B' in Citroen's timing values table. But do remember to halve the value....

Here is an example. This is an extract from Citroen's table of timing values.

Illustrative extract from Citroen's timing table - manual 814

Using a 2347cc DS23 of the 1973 year as our example, (second row here) the table says that the advance timing should be carried out at 2000rpm and the total advance should be 23 crankshaft degrees. That's a total of 23 degrees. Note that column 'C' is empty. The assumption for your DS 23 is that, when setting the advance, you need to set all 23 degrees, because you have been instructed to start with TDC as your static timing point - your 'static setting' as column 'C' calls it is zero.

If you had a DS23 covered by that timing curve and those values, and if you had followed the process I've described here, that is what you would need to do when setting the advance: you would be looking to see 23 degrees. Since you would be using the pulley to set this, you would be wanting to see the mark you made move by half that value '11' 30"

Note also for the first row above (a particular 1985cc 'DV' vehicle) that column 'C' is populated. Why is this? Well that row covers certain vehicles/ engines used both sides of the fateful July 1971 change in flywheels.

• For vehicles in this row but before that date, the static timing position and the white mark made on the pulley already gives 12 degrees. So of the total 24 degree specified, only another 12 remain to be set in the 'advance' process. 12 degrees of crankshaft movement are measured on the pulley as 6 degrees of movement against the gauge: from zero to 6. That's what column 'C' is telling you.
• For vehicles made after July 1971, the assumption again is that you are starting from a zero degree position and will need to set all 24 degrees - just the column 'B' figure.

That's just about the key difference when setting up the timing on post July 1971 cars. Any error in the process is not the fault of 123 ignition per se though the instructions that came with my car were pretty cryptic. It's the Citroen factory workshop manuals that say to start the process from TDC, and fail to suggest that the engine should be/ needs to be 'wound back'. 

FOOTNOTE

Someone has recently sent me PDF (so presumably downloadable) instructions for fitting 123 that are specific to the DS and which do mention the need to 'wind the engine back' 12 degrees before you fit the 123 distributor and rotate it to light the little green LED.

Extract from 123 electronic ignition PDF instructions for Ds

I've also re-read the cryptic generic instructions that came with my 123 and I think that the process outlined would be sufficient for setting the static timing on a DS made after July 1971. The instructions would work.

Generic and cryptic - 123 ignition instructions

Here is what they say in essence:

• Using the distributor cap as the guide, put a mark on the perimeter of your old distributor body that aligns to the 'cylinder 1' HT contact of the distributor cap when it's fitted.
• With the distributor cap removed, crank the engine so that the rotor arm points to the mark you have just made - the point where the rotor arm would cause a spark to number one HT lead if the distributor cap was fired. 
• Leave the engine in this position and replace your old distributor with the 123 distributor
• Twist the 123 distributor anti-clockwise until the little LED light comes on.

What the above process essentially does, is it use the position of the distributor about to be replaced, to find the current timing position of the engine and use that as the static timing position. And because it uses the distributor cap HT lead position for cylinder 1 as the reference point for the mark, when the rotor point to that mark, cylinder 1 must be on it it's compression stroke. So using the position of the rotor against the mark made on the distributor perimeter, is a rough equivalent of rotating the engine so that any mark on the pulley aligns with '6' on the gauge - about 12 degrees before TDC. As such, it should be enough for static timing.

The caveat to this is that the instructions assume the engine hasn't been cranked or otherwise rotated with the distributor out. They rely on the distributor being in the same rotational position as when the engine was last running. That isn't mentioned, but the generic 123 instructions are written from the point of view of swapping out an old distributor - so perhaps that omission is understandable.