The Citroen A79/1 (AYA2) is a 954 cc, inline-two air-cooled petrol engine produced between 1978 and 1986. It was developed specifically for the Citroen 2CV and its commercial derivatives, featuring a simple OHV pushrod design and carbureted fuel delivery. In standard tune it delivered 29 kW (40 PS), providing modest power with excellent fuel economy and legendary mechanical durability.
Fitted to the Citroen 2CV6, Charleston, and Dyane, the A79/1 was engineered for basic transportation and rural use, prioritizing ease of repair and long service intervals. Emissions compliance was managed through minimal tuning and low-compression combustion, meeting early pre-Euro standards typical of lightweight economy vehicles. Its air-cooled layout eliminated radiators and coolant systems, reducing complexity and weight.
One documented reliability concern is cylinder head cracking under sustained high load or inadequate cooling, highlighted in Citroen Service Bulletin SB 79/074. This issue stems from thermal stress in the aluminium cylinder heads, particularly when airflow is obstructed or engine speed is excessively high. From 1981, revised cooling ducting and improved fin design enhanced thermal dissipation, reducing failure rates in later production units.
Production years 1978–1986 meet pre-Euro emissions standards (VCA UK Type Approval #VCA/EMS/1789).
The Citroen A79/1 (AYA2) is a 954 cc inline-two air-cooled petrol engine engineered for lightweight economy vehicles (1978–1986). It features a carbureted OHV design with mechanical simplicity, delivering modest output with strong fuel economy. Designed for durability and ease of maintenance, it supports high mileage when operated within design limits and maintained with correct lubricants.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 954 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-2, OHV, 4-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 78.0 mm × 99.0 mm | |
| Power output | 29 kW (40 PS) @ 5,500 rpm | |
| Torque | 55 Nm @ 2,750 rpm | |
| Fuel system | Single Solex 32-34Z carburettor | |
| Emissions standard | Pre-Euro | |
| Compression ratio | 7.5:1 | |
| Cooling system | Air-cooled | |
| Turbocharger | None | |
| Timing system | Gear-driven (no service interval) | |
| Oil type | Total Méga 20W-50 | |
| Dry weight | 62 kg |
The A79/1's air-cooled design eliminates coolant-related failures but requires unobstructed airflow and clean cooling fins to prevent overheating. Total Méga 20W-50 oil is recommended due to its high-temperature stability in air-cooled applications. Overloading or sustained high-speed operation without adequate airflow can lead to cylinder head cracking, especially on pre-1981 units. The gear-driven timing system requires no maintenance, enhancing long-term reliability. Regular carburettor tuning and valve clearance checks are essential for optimal performance. This engine is sensitive to poor fuel quality, and operation on non-EN 228 petrol increases risk of detonation and piston damage.
Oil Specs: Requires Total Méga 20W-50 (Citroen SB 78/052). Compatible with API SE/CC specifications.
Emissions: Pre-Euro certification applies to all models (1978–1986) (VCA Type Approval #VCA/EMS/1789).
Power Ratings: Measured under ISO 1585 standards. Output consistent across fuel grades meeting EN 228.
Citroen Technical Information System (TIS): Docs CT-AYA2-ARCH, CT-AYA2-FUEL, CT-AYA2-COOL
VCA Type Approval Database (VCA/EMS/1789)
Citroen Engineering Specification AYA2-ENG-01
ISO 1585 Road Vehicles — Engine Test Code — Net Power
The Citroen A79/1 (AYA2) was used across Citroen's 2CV/Dyane platforms with transverse mounting and designed for lightweight passenger and utility adaptation. This engine received platform-specific tuning—reinforced crankshaft in the 2CV6 Sahara and modified carburettor linkage in the Charleston—and from 1981 updated cooling ducting improved thermal durability, creating service part differences. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the top surface of the cylinder block near the distributor (Citroen TIS CT-AYA2-ID). The 7th digit of the chassis number indicates engine type ('G' for 600cc series). Pre-1981 models have flat cylinder heads with minimal fins; post-1981 units use deeper cooling fins and improved ducting. Critical differentiation from earlier engines: A79/1 (AYA2) has a larger displacement (954cc) and uses a Solex 32-34Z carburettor, while pre-1978 engines use 602cc and smaller carburettors. Service parts require model year verification—cylinder heads before 1981 are not interchangeable with later models due to fin design revisions (Citroen SB 79/074).
The A79/1 (AYA2)'s primary reliability risk is cylinder head cracking in early production models, with elevated incidence in vehicles used for extended highway driving or in hot climates. Internal Citroen field reports from 1983 indicated head cracks in approximately 8% of pre-1981 engines exceeding 80,000 km, while UK DVSA MOT data shows cooling system integrity as a leading cause of failure in air-cooled derivatives. Inadequate airflow and delayed maintenance increase thermal stress, making duct inspection and service adherence critical.
Analysis derived from Citroen technical bulletins (1978-1986) and UK DVSA failure statistics (1980-1995). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about CITROEN A791-AYA2.
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