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Citroën A-Type 652cc Conversion

© Copyright: J.Cats.

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@ rpmDIN Nm@ rpm
A06/635602M28/12cv6 / Mehari295750393500
AM2602M28Dyane6 / Ami8325750424000
V06/6??652V06Visa / LNA345250503500

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.

Flywheels
The 2 different type 652cc flywheels. On the left the one for the modern diaphragm clutch, on the right the one for the older 3 finger clutch.

Gearbox

There are 2 different types of (602cc) gearboxes.

  1. Old type gearbox.
    Used 1970-1982. Mostly drum brake gearboxes, some disc brake. Has an input shaft with 20mm splines on it. Can only be used when the old type (pre 1982) 3 finger clutch is fitted to the engine!
  2. New type gearbox.
    Used 1982 onwards. Only exists as a disc brakes gearbox. Has an input shaft with 40mm splines on it. Can be fitted with both type clutches (both 3 finger and diaphragm).

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
  • home-made bracket

Bracket between engine and gearbox
Here the sensor bracket is fitted between the engine and bellhousing on one side, spacers are fitted on the other side. When following this option, be sure to use the 40mm splined gearbox. If not you'll risk the clutch plate running off the splines when it's worn. An advantage is that the flywheel doesn't have to be modified and the gearbox only needs 2 holes drilled for the sensors to poke through. A kit containing the sensor bracket and spacer rings can be bought from most 2cv specialists. Most conversions are done this way. A disadvantage is that the clutch can become difficult to setup as the free travel gets a lot longer.
Attention
There are a number of brackets available that don't put the sensors in the exact position they need to be in. When buying a bracket, check the measurements with the 652cc bellhousing and check the ignition timing after fitting. Incorrect position of the sensors will lead to reduced performance and can result in engine damage. Also check that bracket and spacers are the same thickness.

Bracket on the back of the bellhousing
Here the sensor bracket is fitted on the back of the bellhousing. To get the flywheel to clear the bellhousing it is machined on both sides. 2 holes are cut in the bellhousing so the sensors can be fitted. An advantage is that this solution always give plenty support to the gearbox and the flywheel is nicely lightened. A disadvantage is that the flywheel fitting flange has to be reduced quite a bit, and this is not without risks.

Homemade bracket.
First the flywheel problem. In order to get the flywheel to run freely, the toothed belt is moved. Any decent engine rebuilting shop can push the toothed belt +/- 6mm to the engine side of the flywheel. The flywheel has to be machined for this (the toothed belt can't be moved as is because it sits against an edge on the flywheel). This is quite inexpensive. The belt is heated to take it off and put it back on, the same way Citroën got the belt on. At the same time the flywheel can be lightened and balanced as well. It's now also possible to replace the 652 toothed belt with one from a 602cc flywheel! This way the 602 starter can be used. Detailed description on how to built your own bracket can be found here.

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.

Engine mounts

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.

Solex
Most important is the tube running from the front bottom of the carb to the vacuum sensor. On the right rear corner of the carb there are 2 more hoses, a thick and a thin one. The thick one goes to the damper on the choke valve. The thin one goes to the front connection of the rubber elbow on top of the carb. This last one isn't absolutely necessary but when it isn't connected, the connection on the carb has to be closed to prevent it from sucking in air. On top of the carb lid there is a hole with a thick hose on it. The same hole can be found on the 602 carb but without the hose. When leaving of the hose on the 652 fuel will come out of the hole when going from full throttle to no throttle at high rpm. The hose is connected to the intake to make sure the fuel always gets sucked back into the engine. Leaving off the hose will increase the risk of under bonnet fires and will give a smell of petrol. The rest of the hoses isn't needed.

Weber
Most important is the tube running from the front bottom of the carb to the vacuum sensor. On the rear of the carb there are 2 more hoses. The top one is connected to the damper on the choke valve. The bottom one is connected to either one of the hoses from the rubber elbow on top of the carb. This last one isn't absolutely necessary but when it isn't connected, the connection on the carb has to closed to prevent it from sucking in air. The rest of the hoses isn't needed, which will leave you with one hose from the rubber elbow unconnected to anything.

602 carb
A 602 carb can't be used. Apart from the fact that there is no reason to do so, the 2cv carb just doesn't provide the right amounts of fuel for the 652. Some people use the 602 carb because they don't understand what the vacuum plumbing on the 652 carb is for.

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:

  • Use the 602 airfilter.
    Simply let the 2 652 sump breather hoses connect before feeding the thick hose into the airfilter. This can be done with a suitable T piece or by feeding the thin hose into a small hole in the thick hose. A suitable T piece could be the little "Miofilter" as used on the GS(A). With this option the original airfilter from you car can be used. However the 602 airfilter housing strangles the car's speed, even with the blown filters as found on Ami and Dyane.
  • Use the 652 airfilter.
    All tubes connect right up to this filter. The housing is not very restrictive if it is fed by fresh air and not with hot air from around the engine. Some early 630 engined LNAs have the "blown" airfilter with a connection between engine shroud and airfilter, as found on Dyane and Ami. The biggest problem is that the 652 airfilter is BIG and you probably won't have much room for it. When using the original housing, make sure you also fit the original intake snout (with a valve for hot/cold air)on the filter. The engine won't run properly without it because of resonance in the housing, which just shows how poor design this housing really is. If you can't fit the original intake tube to the airfilter, don't use the original airfilter. A 602 airfilter will run better then!
  • Using a sports airfilter.
    On the carb a sports airfilter is fitted (K&N, Jamex, Green, Piper, etc) using the rubber elbow from the 652 or it can be fitted directly to the carb. The 652 elbow has 2 equally big openings while the 602 elbow has a smaller inlet opening. The sump breather hoses can either be routed into the new airfilter or a seperate special sump breather filter can be used. The seperate sump breather filter does not work well with these engine and will always breath out some oil.
  • Fitting a 602 breather system.
    When you use the breather system as on the 602cc, so without the addtional tube to the airfilter, the engine sump pressure will be much lower then with the visa system, giving less change of leaking.
A good thing for all airfilter configurations is to fit a cold air feed to the airfilter in the summer. For this, the system as found on the Dyane / Ami can be used or a bonnet vent can be fitted or you can make up something of your own. Just make sure the filter is only getting fresh air and plenty of it.

Cutting Bracket Cutting Bracket
K&N filter with GSA miofilter

Electrical

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).

Sensors

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.

Computer

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:
1: vacuum sensor 2: vacuum sensor 3: empty 4: sensor wire top sensor 5: sensor wire bottom sensor 6: + from ignition lock 7: earth and 1 8: - connection on coil

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)
From:To:
- connection batteryTop Sensor (3 wire sensor only)
- connection batteryBottom Sensor (3 wire sensor only)
- connection batteryvacuum Sensor
- connection batteryConnection 1 computer
- connection batteryConnection 7 computer
+ ignition lockTop Sensor
+ ignition lockBottom Sensor
+ ignition lockCoil +
+ ignition lockConnection 6 computer
Top SensorConnection 4 computer
Bottom SensorConnection 5 computer
vacuum SensorConnection 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!

Vacum sensor

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.

Problems...

Are there any downsides to this conversion?
The weakest link in your car with the 652 engine fitted is definetly the gearbox. The gearbox is under heavy strain and thus will not take rough gearchanges, dragracing, wheelspin starts, etc. Such behaviour will definetly cost you your gearbox! Gearboxes with weak synchromeshes will go bad a bit quicker. Make sure your gearbox is filled with the right amount (0.9 liters) of EP80 gearbox oil at all times. Change gearbox oil more frequently then you'd normally would and check the amount of metal on the magnetic sump plug of the gearbox. This will give you a good indication of the condition of your gearbox. For tuned engines it can be a good idea to fit a G series gearbox. Check here for more info.
Other weak elements are tires, wheelbearings, steering parts, driveshafts and king pins.

Howto...

Removing the fan on 652cc engines

  • Find a 50mm long and 6mm diameter solid steel rod.
  • Undo the bolt holding the fan.
  • Put the rod in the hole.
  • Find a M14 Metric fine threaded (1.5mm thread) bolt and put this in the hole, it exactly fits into the thread in the fan backplate!
  • If you can't find such a bolt, a shockabsorber stud has exactly the right thread where it's bolted into the chassis.
  • Put some tension on the rod by tightening the bolt and lightly hit the bolt with a hammer.
  • Repeat this until the fan comes off. They can be very stuck.

Check if the sensors function properly

  • Keep the sensors connected.
  • Make sure the sensor gets + and -.
  • Put an analogue voltmeter on the green sensor wire.
  • Slowly turn the engine.
  • When the pin in the flywheel is in front of the sensor, you should see something like 7 volt on the sensor wire.
  • When the pin in the flywheel is NOT in front of the sensor, you should see less then 1 volt on the sensor wire.
  • If the sensor gives 7 volts all the time or never gives 7 volts, it's broken.

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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