Disclaimer: This page only provides information based on the personal opinion of the author.
The author can't be held responsible for damage in any way that could result from modifications mentioned here.
Many people would like to improve their car's ability to get along better with today's traffic. This means better acceleration, more reserves for overtaking and possibly a slightly higher top speed. For the Citroën A-types (2cv, Dyane, Mehari, Ami) Citroën has a ready made answer in the shape of the 652cc Visa engine.
Different engines and their characteristics:
|Engine plate:||Capacity:||Engine type:||Car:||DIN bhp||@ rpm||DIN Nm||@ rpm|
|A06/635||602||M28/1||2cv6 / Mehari||29||5750||39||3500|
|AM2||602||M28||Dyane6 / Ami8||32||5750||42||4000|
|V06/6??||652||V06||Visa / LNA||34||5250||50||3500|
So what can you expect from this conversion? The top speed only improves a little because of the bad aerodynamics of the A-types. Better streamlined cars such as the Ami will gain more then badly streamlined cars such as the Mehari. What does improve is the acceleration. The 652cc engine has 50Nm torque, this is an improvement of about 25% over the 602 engines. A 2cv originally doing 0-100kmh/62mph in 30 seconds will achieve this in aa little over 20 seconds with the 652cc engine. Low weight cars will improve more then high weight cars. And because maximum torque is achieved at lower rpm, the car will pull better at low rpm.But, do the smart among us say, why change the whole engine if I could just as easily fit the 652 pistons in bored 602 barrels? Well, there are some problems. The 652 has specially coated alloy barrels and the piston rings are matched to this. In a bored 602 barrel, these rings will cause enormous wear in a relative short period of time. There are specialists which offer 650cc (77mm piston) or 670cc (78mm piston) kits for the 602 engine, but in reality the 670cc kit will only equal the performance of the original 652cc engine. This is because not only did Citroën change the capacity, but also the cylinderheads, ignition, camshaft and carburettor have been modified to keep up. The ignition is a fully electronic one giving a stronger spark and you never have to change and adjust the points again. Furthermore, the Citroën 652cc engine is much more durable then the 602cc (3 main bearing crankshaft instead of 2 bearing one and special bearing materials). For more information on just the piston swap, see the tuning page.
We are going to concentrate on fitting the whole engine. Here are the problems:Flywheel
When bolting the 652cc engine to the a-type gearbox the flywheel gets stuck. The teeth on the starter belt touch the bellhousing. The solution to this is given below, however there is are some other things you need to know about these flywheels. There is a different flywheel for each type of clutch both on the 602 and on the 652 engines. So make sure you have the right type of flywheel and clutch on your 652 engine so it will work with your gearbox! 602cc and 652cc flywheels are not interchangeable. The 602cc flywheel has 107 teeth on the starter belt, the 652cc flywheel has 131. The 602cc starter has 9 teeth, the 652cc starter has 10. The 602cc flywheel can't be fitted to the 652cc engine, the 652cc has 6 bolts holding the flywheel, the 602cc only has 5.
There are 2 different types of (602cc) gearboxes.
Fitting the gearbox that comes with the 652cc engine is hardly an option. Both Visa and LNA gearboxes are much longer then the A-type gearbox. The Visa gearbox has no possibility of fitting the brake calipers on it and 2cv driveshafts can not be fitted. The LNA gearbox has the same basic gearboxhousing as the GS(A), but the caliper mounts are not machined and not threaded. This can be altered ofcourse but make sure the disc ends up int he middle of the caliper and the thread is strong enough. The housing is only aluminium alloy, and not easy to cut strong accurate thread in. The LNA gearbox has the same bolt spacing as a 2cv driveshaft, but a GS(A) disc wont fit without machining of the driveshaft attachment flange.Sensors
Apart from matching the 652 flywheel to the gearbox there are some other problems. The 652 ignition uses 2 sensors that are fitted in the bellhousing and get triggered by a steel pin in the flywheel. It's not easily possible to fit the 602 ignition because there is no cam on the camshaft to operate the points. One solution i've seen is to remove the camshaft front cover and drill a hole in the camshaft. The hole is then threaded and a 2cv points cam is fitted using a bolt. But a lot of care has to be taken to drill centrally and straight, and to get the timing exactly right. Also remember that the ignition curve on the 652 is very different from a 602.Solutions
There are several solutions to fitting the sensors:
Bracket between engine and gearbox
Bracket on the back of the bellhousing
Sensor pin clearance
On some bellhousings there is a bit too much metal below the starter. After bolting engine and gearbox together you will find the pin on the flywheel won't pass under the starter. If this is the case on your gearbox, remove a little bit of metal below the starter until the pins passes freely. You can see the amount of room by removing the starter. On some bellhousings there is a reinforcement ridge from one of the starter mounting holes going down which is too thick and also causes clearance problems. With an angle grinder a small amount of metal can be removed here as well to provide sufficient clearance.
On Visa engines, the engine mounts have to be replaced by A-type engine mounts. They bolt straight on. LNA engines already have the proper engine mounts.
Fan and alternator
The 652 engine has a slightly longer and wider alternator belt. The pulleys on the alternator and fan have been modified for this, also to let the alternator run slightly faster on the 652. Most 652 alternators have a built in voltage regulator. Most A-types have a separate voltage regulator on the firewall. 2 voltage regulators won't work together, the car will keep running after turning off the ignition! The easiest solution is to replace the 652 alternator and fan with those from an A-type. If you want to use the 652 alternator, the voltage regulator is taken of the firewall and the wiring is adapted.
Heat exchangers / exhaust
The 2cv heat exchanger pots (with the exhaust running through them) have to be fitted if you want to use the 2cv exhaust collector box under the gearbox. These heat exchangers bolt straight on. The 602cc exhaust is no more a restriction for the 652cc engine as it is on the 602cc engine.
Carburettor and vacuum piping
There is no performance difference between Solex and Weber carbs. Any carb properly adjusted / jetted for the engine will give optimal performance.
The 652 engine is fitted with some nasty vacuum piping. Depending on the engine and carb type there are different layouts.
Airfilter and sump breather
The 652 engine has the same sump breather hose as the 602 but also an additional sump breather hose of smaller diameter. The idea of the sump breather is to keep oil in the sump but have an open vent path for the sump to the outside atmosphere. There are several options to solve the sump breather problem:
Make sure all connections are good and all earths are good. Most stories about unreliability of the system come from bad earth connections to the computer. Make sure you're using the brown Visa/LNA coil. These are specifically designed for the 652 electronic ignition (constant coil soak time).
There are 2 types of sensors. 2 wire: the brown wire is the sensor wire and the green wire is + from the ignition key. 3 wire: the brown/black wire is earth (-), the red wire is + from the ignition key and the green wire is the sensor wire. If your car has earthing problems, the 3 wire sensors will be more reliable, otherwise the number of wires on the sensor doesn't matter. Try using the original connectors on the sensors as much as possible. The sensors can stop working (although rare) so always carry a spare. You'll also need to fit the aforementioned vacuum sensor (often forgotten, it can cost you your engine) This electronic ignition has less problems then the points ignition fitted to 602cc engines.
Besides these sensors there is another crucial sensor, often forgotten. On the Visa/LNA there is a vacuum sensor fitted beneath the bonnet closing mechanism This sensor MUST be fitted for the ignition to work properly. When sucking on the sensor it should connect the 2 contacts (so it doesn't matter which wire is connected where on the sensor). When the engine exceeds 1000 rpm and there is enough vacuum in the manifold, the ignition gets advanced 10 degrees. When omitting this sensor, the car will be unable to reach top speed and pinking can occur, eventually destroying the engine. Regularly check to see if the sensor is working properly.
There are 2 computer types, VA1 VD1 and VA4 VD4. I suspect the VA4 VD4 box is intended for the V06/664-665 lead free 95 octane engine. For running on this fuel, a different ignition timing is needed. However it's not so that ANY engine will run on 95 unleaded when using this computer. The V06/630 and V06/644 both work with both type of computer, the VA1 VD1 is best on these engines. The computer is best fitted beneath the dashboard to keep it cool and dry. Make sure the sensor wires are kept away from the high tension wires.
To wire in the computer, you need the original multi wire plug with some lengths of wire still attached.
With the plug fitted, turn the box upside down, wires are now pointing upwards.
On the plug are numbers 1 to 8, left to right.
If not, the number 3 position can be used for identification.
Here is what each position is for:
The "+ from ignition lock" is best taken from the wire originally only going to the coil (+ connection). This additional branch will go the computer, both sensors and the shut off valve.
|Wiring overview (drawing)|
|- connection battery||Top Sensor (3 wire sensor only)|
|- connection battery||Bottom Sensor (3 wire sensor only)|
|- connection battery||vacuum Sensor|
|- connection battery||Connection 1 computer|
|- connection battery||Connection 7 computer|
|+ ignition lock||Top Sensor|
|+ ignition lock||Bottom Sensor|
|+ ignition lock||Coil +|
|+ ignition lock||Connection 6 computer|
|Top Sensor||Connection 4 computer|
|Bottom Sensor||Connection 5 computer|
|vacuum Sensor||Connection 2 computer|
|Coil -||Connection 8 computer|
On the carb is a shut off valve. This valve closes the idle jet when the ignition is turned off. It very common for this valve to fail, making the engine unable to idle. In this case the valve can be removed, the idle jet taken off, the moving pin cut off completely, idle jet refitted and the valve refitted to the engine but not connected. The car will run perfectly with the valve disabled like this!
There is a wide variety in the amount of vacum needed to get the different vacum sensors to switch. Therefor a few people have disconnected the vacum sensor completely. Both terminals on the computer going to the vacum sensor are connected to ground. Under 1500 rpm the ignition curve is identical to running with a disconnected vacum tube. Above 1500rpm the full 10degrees additonal vacum advance is added to the ignition curve. Theoretically too much advance at low rpm can cause trouble but sofar no problems have been found running with grounded vacum sensor terminals.
Are there any downsides to this conversion?
Removing the fan on 652cc engines
Check if the sensors function properly
Quite a few people have used this page to do the conversion succesfully. With their and your feedback this page has been and will keep being adapted to make it even better.
Do you have any comments, questions or suggestions?
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