Correcting the Timing Curve of the Distributor
There is a seven page article by Jerry Hathaway titled "SM Ignition System" that covers complete setup of the distributor, in the Winter 2002 issue of the Citroën Quarterly. This is Vol. 20 #1.
Timing Curve of the Distributor
There are three curves: 2.7L, 3.0L, and IE..
|Engine||Degrees @ RPM||Degrees @ Idle|
|2.7L||29 @ 2000||5-7|
|3.0L||26 @ 2000||5-7|
|IE||22 @ 2000||5-7|
- The advance above is approximately when the free play in the stiff spring is used up, and both springs are in use above this speed. Hence, set the timing as above, then rev a little more and there should be very little increase.
- In carburetter equipped cars, wear on the strong spring post is very common and leads to excessive advance if timing is set at idle.
- In carburetter equipeed cars, wear on the weak spring itself is very common and leads to unstable idle as the distributor will begin to advance at below idle speeds.
- Think carefully and bend the advance spring posts slightly as needed. Replacements for the weak spring are available.
- If the car is very original with all anti-pollution fitted, and the distributor has a timing point at idle stamped on it, then keep to the above table but also the markings on the distributor.
- I.E. cars have two identical springs and do not suffer as above. However the vacuum retard capsule is often faulty. If still operating it can be adjusted by turning the hex bar inside. Idle is 1 deg ATDC with the vacuum connected, as above not connected.
- The rotor has resistors in carriers inside the rotor, with several pressure only contacts. The contacts can go high resistance and cause problems.
Rumor has it that Ralph Cudworth used to suggest digging them out when they were bad and replacing with bits of nail.
(Keeping it stock)
- There is nothing inherently wrong with the stock system. Although the individual components are expensive (caps can cost upwards of $400, rotors $150, and points $150 each) they are of good quality manufacture. The design was superior in its day, similar to distributors found on 12-cylinder Lamborghinis of similar vintage. It is essentially two concentric three cylinder distributors, each operating a single coil firing alternately. Because each coil fires only half as often, dwell time and coil saturation are improved over what was possible at the time with a single coil distributor. Because of the dual circuit design, however, the outer ring of the rotor has a not-insignificant surface speed relative to the coil contact. This can cause the outer contact to wear and as the contact pressure decreases, the outer contact can arc to the outer ring and damage it. The solution is to repair the cap by replacing the outer contact (salvaged from an air cooled VW Beetle cap) before damage to the rotor occurs.
- Drill a hole in the side of the distributor to allow dwell to be set while it is assembled
- See Lumenition
- Designed for the SM; reversible; stable
- Full distributor replacement
This modification utilizes a 1960's Buick Skylark V6 "Dauntless" 225 "odd fire" distributor. In addition, from 1966 until 1971, Jeep used the Buick 225 V6 as the optional engine in CJs. The centrifugal advance weights, located under the rotor, need to be modified. The Buick distributor shaft needs to be adapted for the SM distributor gear.
The standard Buick Skylark Dauntless engine rotation is clockwise, so the centrifugal weights need to be reversed to open in the Citroen SM counter clockwise rotation. The distributor will be able to run utilizing standard Buick points or it can be converted to the Pertronix electronic ignition. The Pertronix part number is 1165, which is for the Jeep or Buick 225 odd-fire engine.
See Buick/Pertronix 1165 below for more information.
Delivers twice the voltage to the spark plugs, increasing horsepower, fuel economy, and spark plug life. 2:1 improvement over “points” in current fall time for increased coil output. Rotating cobalt magnets trigger a Hall Effect integrated circuit . ...no points to burn, ...no moving parts to wear out. Epoxy molding makes our module impervious to dirt, oil, grease and moisture. Fits entirely inside the distributor. No "black box” to clutter the engine compartment. Stable timing ...no need for any adjustments. Will trigger most multi-spark CD ignitions. Use with Flame-Thrower® 40,000 volt coil for optimal performance.
For over thirty years, the Ignitor has proven itself in applications ranging from race cars to tractors. The Ignitor replaces breaker point and troublesome factory electronic ignitions with a dependable, self contained and maintenance free electronic ignition system. The Ignitor has been called the "stealth" ignition because of its quick installation and nearly undetectable presence under your distributor cap.
Above is a photograph of the Pertronix 1165, odd-fire electronic ignition kit. The kit consists of two parts, the cobalt magnetic ring on the left, and the igniter on the right. The notched cobalt magnetic ring is installed under the Buick centrifugal advance weight plate. The notched magnetic ring contains the cobalt magnets that are properly spaced for the Citroen SM odd-fired engine. Insure the notch in the ring is correctly placed, otherwise you will be 180 degrees out of sync. The Pertronix 1165 instructions show proper placement. Remove the stock odd-fire rotor screws, then the two studs on the magnetic ring will pass through the centrifugal weights plate to attach to the stock Buick odd-fire rotor with two included nuts. The correct igniter pickup gap is adjusted by placing spacing washers on the studs between the magnetic cobalt ring and centrifugal advance plate. The igniter is attached to the stock Buick odd-fire points location.
Another point that needs mentioning is the requirement of a divide by two circuit for the SM tachometer. Without this circuit, the tach will read twice the RPM's, since the Buick odd fired distributor will be running on only one Pertronix Flame thrower coil, vs the stock SM dual coils.
John Titus now offers a drop-in kit to install the Pertronix 1165 into the SM Distributor. For more information, see marketplace:John Titus#Pertronix Ignition System
Using the Petronix ignitor for air-cooled VW engines provides the correct dwell for the SM ignition.
- Complete distributor replacement. Dutch invention, see the 123ignition web site. The 123 distributor is newly produced. Even the cogwheel. The electronics inside replace the flyweights all together and middle the ignition moments between cylinders compared to the RPM the engine is doing. It uses cheap bosch rotor and cap. So no moving parts except for the central axle. It drives a standard single coil. It has an output for the rev counter and the D-Jetronic.
Will no longer be produced due to overheating problems with the first revision.
Titus HEI Conversion
- This is a single coil solution based on General Motors HEI components. The HEI pickup and reluctor from a late model Buick are matched with an early small body Buick distributor cap and rotor in a custom distributor housing. Also available in an EFI version that includes the trigger points for the D-Jetronic. For more information, see marketplace:John Titus
Van Rootselaar Technic used to make a single coil solution, based on standard Bosch components. It's unknown whether this system is still being manufactured.