Measuring distributor advance and setting the ignition timing with a stroboscopic timing light on Citroën D models
One of the basic, yet most important steps in a proper tuneup on any car is setting the ignition timing. On a Citroën D, this is no simple task. Most of us have avoided the problem by resorting to time-tested methods based on guess-and-by-golly, or perhaps on more refined, yet not exacting methods such as turning the distributor to obtain maximum power, yet avoid ping or "pink", as Europeans have tended to say.
A great deal of time and effort has been expended on this vague aspect of maintaining our cars. This need not be. The fact that our cars went through most of their design life with no timing marks is absurd, but that does not deter us from loving them. In fact, it adds to their uniqueness and it should also add to the satisfaction of answering the challenge of getting our cars running tip-top. Even those of us with cars that came with timing marks may be daunted by the timing procedure. I have decided to make an attempt to de-mystify this vital step in getting all of the power and reliability we can from our cars. To perform a basic tuneup you will need:
Let's start with the basics. We will assume that the car we are discussing has been unaltered and that it has all of its original parts. Every engine that comes off the assembly line has a carburetor and a distributor matched to give optimum performance. Ignition timing is controlled by interaction of the distributor and the rest of the engine, while the carburetor must deliver the right ratio of fuel and air in every condition. The first step in any tuneup is to install a fresh set of points and a healthy new condenser. The new point set should have a dab of high temperature grease applied to its bumper so it does not wear excessively as it rubs against the distributor cam. Old grease should be removed from the cam, and the distributor should be in good condition. The point gap must be set to specifications. While a dwell meter can be used, it is more important that the gap be wide enough so that, as cam bumper wear inevitably occurs, it does not make the gap close prematurely. This is why I simply set them to the maximum allowable opening. This, along with proper cleaning and lubrication of the point bumper/cam, ensures a long lasting tuneup.
If you own a Citroën D, you should by now be fully aware of the lack of technical support in places such as the United States. It therefore behooves us to be armed with all of the necessary tools to maintain your own cars. Despite the seeming complexity of the D, for the most part, they are not that difficult to work on and they are famously robust (except for rust). One of the most important tools to have is a complete set of manuals. The other indispensible tool is the Citroen D email list at CitroenDSID. Subscription is free and really risk free. There you will be able to get in contact with people who can solve most any problem you may encounter.
Once the distributor has been properly serviced, it must be installed in the car and set to static time. Because D's have no external timing marks, except for the latest ones, the flywheel must be locked into position and the distributor set using a test light. A specially made pin (B) or a 6 mm drill bit is inserted into a hole in the flywheel housing, hidden under the alternator. It is a rite of passage for D owners to discover that diabolically hidden timing hole. Once you find it, you will swear that you can now find the Holy Grail! The first time is the hardest time to find this hole. You may have to remove the left front fender to be able to see it. Later, you might get away with a strategically placed light and a mirror. This alone is reason enough to switch to using a timing light!
The flywheel must be rotated until the pin drops into a slot in the flywheel, locking the crank at a specific point, then set the distributor can be rotated until the points just open. Touch the tip of a test light between coil (-) and a good ground. If the ignition switch is turned on, the light should glow when the points are opened. This is where many of us stop, and the car will run, but not as well as it should. The C&A manual clearly states that the timing should then be set with a strobe light to complete the job. Whenever you use this pin, make absolutely certain that you remove it before you start the engine or try moving it in any way. The pin will break off and the end will stay in the slot of the flywheel, damaging your engine!
Most any other car has a ready means of setting the ignition timing using a strobe light. Here is where it gets tricky for a D owner. Our cars have no access to a component that spins at crank speed. The flywheel is buried, and there is no drive pulley off the timing chain end of the engine, which is pointing rearward. However, there is an accessory drive pulley that runs off the camshaft, which spins at exactly half the speed of the crank, and that is what we will use. But timing specifications are almost always stated in crank degrees, so setting time from the position of this pulley will require this factor to be taken into account. 20 degrees of crank movement will produce 10 degrees of camshaft/drive pulley movement.
To add to the confusion, for U.S. spec cars, the static timing point is 0 (TDC) starting in November, 1967. Cars built for the European market have the static timing point on the flywheel set to 12° before top dead center (BTDC). In July, 1971 European cars caught up to U.S. spec emission requirement and they too changed their flywheels to TDC. On fuel injected engines built after July, 1971, the offset is 8 degrees, 30 minutes BTDC. These factors must be accounted for when calculating the strobe timing point. As you will see, you cannot just subtract 12 and get the right timing point.
Compensating for the advance curve of the distributor piles on even more confusion. As I stated earlier, every engine has been matched at the factory with its own distributor. A quick look at the advance curves shown in the C&A manual will show that the advance curve on many of our cars begins very soon after 0 rpm and moves upwards at varying rates and ends at varying speeds. This is controlled by the advance mechanism located under the points plate in your distributor, which is rotated to effect timing during various driving conditions. The mass and shape of the weights, the strength of the springs and the location of the stops determine the advance curve for each distributor and are specific to engine type and year. Because the timing begins to change as soon as the engine begins to run, if you simply set the time at idle speed, you will get an inaccurate reading. This is why we must determine the maximum advance speed and set our time while the engine is running above that point using the advance curve specifications specific to our cars. To proceed, we will need some tools. We will need
Here is the one I
made. All of the
parts came from the local hardware store. The tool is made from a "T"
bracket and a narrow piece of aluminum flat stock. The base leg is bent
90° while the ends of the other 2 are shortened slightly and curved to
follow the radius of the pulley. The bar is cut to required length and
bends in it to allow clearance and proper offset. First the bracket is
attached, then tilted to the correct angle. Then this assembly is held
the alternator tensioner and marked from behind for drill hole so
face of the timing tool is just away from the pulley. A screw goes
front of this hole, through the slot in the alternator tensioner brace,
oversized nut for spacer, a washer, then a nut to secure all. When
with fit, tape and/or glue a timing plate made from paper. Marks are
apart. Each increment equals 2 deg. The tool must not rub or interfere
various moving parts, yet hold the scale close to the edge of the
The flywheel is then locked into static time position using the hole in the flywheel housing and the pin. Whenever you use this pin, make absolutely certain that you remove it before you start the engine or try moving it in any way. The pin will break off and the end will stay in the slot of the flywheel, damaging your engine! Use a sharp punch to make a clear mark on the edge of the pulley adjacent to the "0" point on the scale, or just use a dab of bright paint. Remember that this does not necessarily represent TDC. It is merely a reference point, unless your engine happens to have TDC static time.
Now we can apply some basic mathematics to this situation. Remember that the distributor runs off the cam and is also turning at half the crank speed, therefore distributor time is the same as cam time. For the sake of demonstration, lets pick out one of the advance curve charts located in the 814 manual. We will work on a 1967 DX European spec. engine. The correct chart for this engine C-6, which appears to top out at 9 degrees distributor time at 2500 RPM. To obtain crank time, we double this number. Then the static timing point must be subtracted to negate the offset caused by the static timing point. The resulting number must again be divided by 2 to convert back to cam time. So:
if D = maximum
distributor degrees (same as cam degrees) and
S = static timing offset, then
2D - S / 2 = T
T being the reading at a scale mounted on the accessory drive pulley.
If D = 9 and
S = 12 , then
2 x 9 - 12 / 2 = 3.
With this, you simply set the distributor rotation to 3° on the scale at 3000 r.p.m.
This chart can be used as a guide to set time on any D engine, even the dual point 3 bearing engines found in Traction Avants and early D's. Click Here. This chart, along with the timing advance graphs located in the C&A manual, may help you to find the correct distributor for your engine, should you find that yours is incorrect or damaged beyond repair. Fortunately, there is not a really large number of possibilities, and the distributor numbers are also located there to help you in your search. Remember that the correct advance curve matched to your engine along with accurate timing will give you optimal performance and efficiency at all speeds.
For owners of U.S. spec cars, the job is just a bit more of a challenge. For cars built before 11/67, the Euro timing curves should be OK for U.S. cars and therefore, you can use the Euro procedure. Until November of 1967, the static timing offset is the same as European cars, when they begin using a flywheel with TDC timing set point. I have Service Bulletin L-160, which has a curve for the 1967 U.S. spec. DV motor. The curve is identical to the one found at chart C8, as found in op. 210-0 in the C&A book. This formula also works with European cars built after July, 1971, except fuel injected cars built after July, 1971, which retain an offset, S= 8°30'. Since U.S. spec cars after 11/67 have their timing holes at TDC, the static point correction need not be done. But the formula still holds.
2D - S / 2 = T, with S=0 so
2D/2 = T or just
D = T
It may seem therefore, that a timing light is not necessary, but to get repeatable, accurate timing and to avoid the necessity of using a flywheel locking pin and test light, this is still far more practical. Even though we lack our advance curve charts, all is not lost; we simply will need to go one step further. We must discover our maximum r.p.m.'s and your maximum advance. The following procedure will reveal this. You will need to have your scale mounted, your zero point marked on the accessory pulley using the flywheel pin and test light. Attach a tachometer and a timing strobe light to your engine. Start the engine and point your light at the pulley and scale. Make certain that you have not left the flywheel locking pin in, if you first set your static timing point. Begin to rev the engine slowly upward. You should not have to go beyond 3000 r.p.m. As the speed increases, you should see the timing mark begin the climb up the scale. Write down the maximum degrees and note your r.p.m.'s at that point. This is your maximum advance. From now on, you can set your time to this point using just your timing light. If you are not sure that the distributor is correct for your engine, this procedure can also be used to construct your own advance chart. Simply note advance at several r.p.m.'s and lay out your results on a chart like the ones in the manual. You can then easily compare yours to the book's.
Using a timing light is not only practical, but it is a foolproof way to reset our engines to proper time on a consistent basis during tuneups and other types of engine work. Even if you find that regional differences in fuel quality, altitude, variations in the condition of our engines, distributor mismatch or any other factor still cause our engines to ping, we can at least have a known starting point for our adjustments.
While I am pretty sure that I have this all reasoned out pretty thoroughly, and I have written it in a way that I hope you will be able to understand, I am open to suggestions. If you find discrepancies or if you can offer some constructive criticism, please email me.
updated 03/12/2021, Copyright 2021, Mark
Many thanks to Rick Levy and Joe Conte for their technical help and their keen eyes!