Gearboxes in Citroën flat air-cooled engines

The Citroën flat air-cooled engines all seem* to have gearboxes that can be mated to an A series engine. This means it’s theoretically* practical to interchange gearboxes. However, before attempting this it’s worth knowing what ratios are in the different boxes.

* So I’ve read – I’ve not tried it.

This is a summary of the information I’ve been able to find about the different gearboxes and their ratios from a variety of sources. Where it’s been available to me I’ve take the information from Citroën workshop manuals, the rest is from various corners of the internet (mostly French Wikipedia 1,2,3) so…

CAVEAT LECTOR

This information is provided as-is with no guarantee of accuracy. Your mileage may vary, the value of investments may go up as well as down, the only certain things in life are death and taxes.

Table of contents

  1. A series engines
  2. M series engines
    1. 2CV 6
    2. Dyane 6
    3. LN
  3. V series engines
    1. Visa
    2. LNA
  4. G series engines
    1. GS 4 speed
    2. GS 5 speed
    3. Axel 11R
    4. Axel 12TRS

A series engines

This is the engine that debuted with the 2CV in 1949 and powered the 2CV 4. I’ve not included details of the gearbox on these but there are quite a few listed in the workshop manual.

M series engines

This is the base model, two cylinder, 602cc, engine that first appeared in 1961 in the 2CV 6. It is an evolution of the A series engine.

There seem to have been a variety of gearboxes for the different models produced (Mehari, vans, &c.) so to simplify things I’ve stuck with the post 1970 2CV 6 and Dyane 6 as they’re the most common.

2CV 6 (from 1970)

Engine: M28/1, 602cc flat 2, 8.5:1 compression ratio.

Tyres: 125 R 15 X, 1.8000m rolling circumference under load.

Gear Gearbox ratio Final drive Overall ratio Speed at 1000 rpm kph Speed at 1000 rpm mph
1st 5.202 4.125 21.458 5.033 3.145
2nd 2.656 4.125 10.956 9.857 6.160
3rd 1.785 4.125 7.363 14.667 9.166
4th 1.315 4.125 5.424 19.911 12.444
Rev 5.202 4.125 21.458 5.033 3.145

Speedometer drive ratio: 4/16

Dyane 6

(& Ami 8?)

Engine: M28, 602cc flat 2, 9:1 compression ratio.

Tyres: 125 R 15 X, 1.8000m rolling circumference under load.

Gear Gearbox ratio Final drive Overall ratio Speed at 1000 rpm kph Speed at 1000 rpm mph
1st 5.748 3.875 22.275 4.848 3.03
2nd 2.934 3.875 11.372 9.497 5.935
3rd 1.923 3.875 7.451 14.816 9.26
4th 1.350 3.875 5.231 20.646 12.903
Rev 5.748 3.875 22.275 4.848 3.03

Speedometer drive ratio: 4/16

LN

Engine: R06/627 (re-badged M28), 602cc flat 2, 9:1 compression ratio.

Tyres: 135 SR 13 XZX, 1.670m rolling circumference under load.

Gear Gearbox ratio Final drive Overall ratio Speed at 1000 rpm kph Speed at 1000 rpm mph
1st 4.55 4.375 19.91 5.2 3.2
2nd 2.5 4.375 10.94 9.5 5.9
3rd 1.81 4.375 7.92 13.1 8.1
4th 1.15 4.375 5.03 20.7 12.9
Rev 4.18 4.375 18.29 ??? ???

V series engines

Normally referred to as the Visa engine, this is an evolution of the M28 A series engine with changes to the major components (crank case, crank, cylinders, heads, ignition).

Visa

Engine: V06/630, 652cc flat two, 9.1:1 compression ratio.

Tyres: 135 SR 13 XZX, 1.670m rolling circumference under load.

Gear Gearbox ratio Final drive Overall ratio Speed at 1000 rpm kph Speed at 1000 rpm mph
1st 4.545 4.125 18.749 5.344 3.321
2nd 2.500 4.125 10.312 9.716 6.038
3rd 1.642 4.125 6.776 14.784 11.674
4th 1.147 4.125 4.731 21.176 13.160
Rev 4.181 4.125 17.249 5.808 3.609

Speedometer drive ratio: 5 X 12

Engine: V06/630, 652cc flat two, 9.5:1 compression ratio.

Not got information on the gearbox, presumably the same as the LNA with this engine?

LNA

Engine: V06/630, 652cc flat 2, 9.1:1 compression ratio.

Tyres: 135 SR 13 XZX , 1.670m rolling circumference under load.

Gear Gearbox ratio Final drive Overall ratio Speed at 1000 rpm kph Speed at 1000 rpm mph
1st 4.55 4.125 18.77 5.5 3.4
2nd 2.5 4.125 18.77 10.1 6.3
3rd 1.64 4.125 6.76 15.4 9.6
4th 1.15 4.125 4.74 21.9 13.6
Rev 4.18 4.125 17.24 ??? ???

Engine: V06/644, 652cc flat 2, 9.5:1 compression ratio.

Tyres: 135 SR 13 XZX , 1.670m rolling circumference under load.

Gear Gearbox ratio Final drive Overall ratio Speed at 1000 rpm kph Speed at 1000 rpm mph
1st 4.55 3.889 17.70 5.5 3.4
2nd 2.5 3.889 9.72 10.1 6.3
3rd 1.64 3.889 6.38 15.4 9.6
4th 1.15 3.889 4.47 21.9 13.6
Rev 4.18 3.889 16.25 ??? ???

G series engines

This is the flat four engine that first appeared in the GS in 1970 and was the main engine in both the GS and Axel as well as powering the Ami Super.

I haven’t done all the cross-referencing required to match GS models to gearboxes but it looks like there were four and five speed gearboxes that came with either a 4.375 or a 4.125 final drive. (There was also a three speed automatic box but I’m not interested in that.)

The Axel was the final evolution of the Citroën flat air cooled engine and seems to have used the four and five speed boxes from the GS but with a final drive of 3.889 in both cases.

Ami Super

Engine: G10/612, 1015cc flat 4, 9:1 compression ratio.

Tyres: 135 SR 15 ZX, 1.821m rolling circumference under load. (?)

Gear Gearbox ratio Final drive Overall ratio Speed at 1000 rpm kph Speed at 1000 rpm mph
1st 3.818 4.125 15.75 7.2 4.5
2nd 2.313 4.125 9.54 11.9 7.4
3rd 1.524 4.125 6.29 18.1 11.2
4th 1.12 4.125 4.62 24.6 15.3
Rev 4.182 4.125 17.25 ??? ???

GS 4 speed

Tyres: 145 SR 15 XZX, 1.873m rolling circumference under load.

Gear Gearbox ratio Final drive Overall ratio Speed at 1000 rpm kph Speed at 1000 rpm mph
1st 3.818 4.375 16.7 7 4.4
2nd 2.313 4.375 10.12 11.5 7.1
3rd 1.524 4.375 6.67 17.5 10.9
4th 1.12 4.375 4.9 23.8 14.8
Rev 4.182 4.375 18.30 ??? ???
Gear Gearbox ratio Final drive Overall ratio Speed at 1000 rpm kph Speed at 1000 rpm mph
1st 3.818 4.125 15.75 7.4 4.6
2nd 2.294 4.125 9.46 12.3 7.6
3rd 1.5 4.125 6.19 18.9 11.7
4th 1.031 4.125 4.25 27.4 17

GS 5 speed

Tyres: 145 SR 15 XZX, 1.873m rolling circumference under load.

Gear Gearbox ratio Final drive Overall ratio Speed at 1000 rpm kph Speed at 1000 rpm mph
1st 3.818 4.375 16.7 7 4.4
2nd 2.294 4.375 10.04 11.6 7.2
3rd 1.5 4.375 6.56 17.8 11.1
4th 1.133 4.375 6.56 23.5 14.6
5th 0.912 4.375 3.99 29.2 18.1
Gear Gearbox ratio Final drive Overall ratio Speed at 1000 rpm kph Speed at 1000 rpm mph
1st 3.818 4.125 15.75 7.4 4.6
2nd 2.294 4.125 9.46 12.3 7.6
3rd 1.5 4.125 6.19 18.9 11.7
4th 1.133 4.125 4.67 25 15.5
5th 0.912 4.125 3.76 31 19.3

Axel 11R

Engine: G11/631 engine, 1129cc flat four, 9:1 compression ratio.

Tyres: 145 SR 15 XZX, 1.873m rolling circumference under load.

Gear Gearbox ratio Final drive Overall ratio Speed at 1000 rpm kph Speed at 1000 rpm mph
1st 3.818 3.889 14.85 7.2 4.5
2nd 2.294 3.889 8.92 12 7.5
3rd 1.5 3.889 5.83 18.4 11.4
4th 1.031 3.889 4.01 26.7 16.6

Axel 12TRS

Engine: T13/653, 1299cc flat four, 8.7:1 compression ratio.

Tyres: 160/65 R 340 TRX (???)

Gear Gearbox ratio Final drive Overall ratio Speed at 1000 rpm kph Speed at 1000 rpm mph
1st 3.818 3.889 14.85 7 4.4
2nd 2.294 3.889 8.92 11.6 7.2
3rd 1.5 3.889 5.83 17.7 11
4th 1.133 3.889 4.41 23.5 14.6
5th 0.912 3.889 3.55 29.1 18.1

Solex 23/36 CISC carburettor

The Solex 23/36 CISC carburettor was fitted to the 2CV, Dyane, Visa and LN(A).  Leaving aside the 652cc engines, there were two models fitted to the 602cc engines and they differ in the sizes of the chokes.

Information on these in the Citroën workshop manuals is contained in a few cross referenced tables which are just about intelligible if you are looking for information on a specific car but make it very hard to come up with a simple guide.  Not that I’m going to let that stop me – here’s my working overview of the main types of 23/36 carbs.

Car Reference First choke venturi [mm] (area [mm^2]) Second choke venturi [mm] (area [mm^2]) First choke main jet Second choke main jet Idle jet First choke air correction jet Second choke air correction jet Pump injector Needle valve seat
2CV/Dyane (1978-07)   197   21 (1385)   24 (1810) 120    70    40 1 F 2 2 AA   40 1.7 (Ball type)
2CV/Dyane (1980-07)/LN 225   18 (1018)   26 (2124) 102.5   87.5   39 1 F 2 2 AA   45 1.7 (Ball type)
Visa/LNA              209   21 (1385)   26 (2124) 125  130    41 120  160   40 170 (Ball type)

Notes:

Car: This is the car that used this carb, this is a rough guide – for more detailed information you’ll need to dig into the workshop manuals.
Reference: The Solex reference that is supposedly on the carb, not found it on mine yet.  However, the venturi sizes are moulded onto the bowl either side of the Solex logo and that’s how you can tell which model you have.

The 197 (21-24) carb is sometimes referred to as a “Dyane carb”, probably because it seems to have first appeared on the M28 engine used in the Dyane. However, both 2CVs and Dyanes had this carb and then the latter – and more common – 225 (18-26) carb.