Ignition
From Citroen-SM-wiki
Contents |
[edit] 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.
[edit] 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 little increase in advance even up to max rpm.
- Wear on the stiff spring post is very common and leads to excessive advance if timing is set at idle.
- Think carefully and bend the advance spring posts slightly as needed.
- 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 wear 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.
[edit] Distributor Rotor
- The rotor is a resistive type with a 5k ohm high voltage wire wound resistor in each circuit.
There are two types (interchangeable) of rotor, the early one made of bakelite with four 'fan' blades and later & more reliable modern plastic with 3 blades. It is this latter that the Lumenition electronic igniton kit is designed to be used with.
The biggest problem with the rotor is 'old-age' oxidation of the metal to metal contacts (a chain of 3 for each resistor) from slip-ring to tip. This causes local heating and then flash-over and eventual failure, oftenby punch-through between the circuits. Careful use of colloidal silver paint can help. You can also reduce HT the stress on the rotor by keeping the two ignition circuits correctly synchronised and timed.
Rumor has it that Ralph Cudworth used to suggest digging them out when they were bad and replacing with bits of nail.
[edit] Contact breakers
- There are two types of contact breaker cassettes, a plastic moulded (original version) and a later metal sided assembly. If possible upgrade to the later version, it is MUCH easier to work with.
The breakers are best and most easily adjusted with a 17mm round inserted into them, which allows the gap to be set. This is very easy on the later type, and more difficult on the plastic ones as they tend to 'snap back' to a previous position. If you have to use the plastic ones, leave them 24 hours after adjusting them, and check again before use. In this case a 'Diamond Deb' nail file is very useful for cleaning the contact faces, and even for slightly evening the gap.
Standard contact breaker clearance of 14-16 thou is fine.
When correctly adjusted they are fine in service and will run 10k plus miles without further work.
[edit] Ignition Coil
- Ducellier 2772c (post 7/71)
Expected resistance at 20 degrees C:
- Primary circuit 1.32 ohms (+/- 0.06 ohms)
- Secondary circuit: 7500 ohms (+/- 1000 ohms)
See http://citroensmpassion.free.fr/ch10/A/allumage/caracter/infospra.html for more information.
[edit] Ignition Conversions
[edit] (Keeping it stock)
- There is absolutely nothing wrong with the stock solution provided all components really are in 100% condition and adjusted correctly. The lifespan of components is good. The design was fundamentally superior in its day. It is essentially two concentric three cylinder distributors operating on a common shaft, similar to the distributor on V12 Lamborghini engines of similar vintage. Two coils and two sets of points are used, meaning that the spark is always high intensity as the coils have plenty of charging time. Remember at any RPM each coil is only firing 3 cylinders instead for 4 or 6 or even...8!
- The distributor can wear, both the advance spring posts and the spindle can descend into the body. Easily rectified by very small bending of the stiff spring post and shimming the spindle back up.
- The distributor cap is very reliable and very rarely fails. If the first version (bakelite) has carbon tracked, get a later one. If the brushes have been burned off by not running on the rotor, check the distributor spindle for the need to shim it back to height. The distributor cap replacement cost is astronomical, so it may be worth while to attempt a repair. Buy one or more VW beetle cap and use the brushes from that!
- The rotor is also fairly expensive to replace. It is, however, possible to take the slip rings out of the rotor using a dental pick in order to attempt some repairs. Each has to be taken on its own merits.
[edit] Minor modifications
- Drill a hole in the side of the distributor to allow dwell to be set while it is assembled
[edit] Lumenition
- See Lumenition
- Designed for the SM; reversible; stable
- As with all electronic ignition systems, it delivers a higher voltage spark than the original distributor owing to the sharper voltage rise and fall times and higher primary current achievable with transistors as opposed to mechanical points.
[edit] Buick
- 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.
[edit] Buick-Pertronix
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.
Below are two modiifed Pertronix 1165 installations into the stock Citroen SM distributor to maintain original appearance.
[edit] 123
- (Notes...)
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.
But...
Will no longer be produced due to overheating problems with the first revision.
[edit] Titus HEI Conversion
- This is a single coil solution based on GM Delco parts. The conversion consists of a custom distributor body that houses the pickup and reluctor from an HEI odd-fire Buick, together with the cap and rotor from an early non-HEI odd-fire Buick. Consequently, it retains the small body of a non-HEI distributor, but is all electronic and uses all Delco parts, which are reliable, inexpensive and readily available. Fast switching time and greater primary current of HEI transistor delivers a higher voltage spark using a single coil than the original distributor delivers with two.
- See Marketplace page for more photos and details.
[edit] Van Rootselaar
Van Rootselaar Technic Makes a single coil solution, based on standard Bosch components. This is a very stable solution and you can buy replacement parts at any store (van Rootselaar also makes a replacement ignition for the NSU RO80 wankel engine).
It can now be bought through SM-Ignition.com a site built by Nard van der Meer, co-owner of Renard Automobiles ([1] an independent Citroën-Peugeot specialist in the Netherlands.
