The Citroen A79/0 (AYA) is a 954 cc, inline-two naturally aspirated petrol engine produced between 1982 and 1990. It features a two-cylinder OHV configuration with a carburettor fuel system and belt-driven camshaft. In standard tune it delivered 25 kW (34 PS), providing basic urban mobility in lightweight city cars.
Fitted to models such as the Citroen AX, C15, and Visa, the A79/0 was engineered for minimal fuel consumption and low manufacturing cost in entry-level applications. Emissions compliance was achieved through simple air injection and catalytic converter systems, allowing the engine to meet early Euro standards in its final production years.
One documented concern is camshaft belt failure due to tensioner degradation, noted in PSA Technical Bulletin PT-M-066. This issue arises from prolonged exposure to heat and oil contamination, particularly in high-mileage examples. From 1987, revised belt material and tensioner spring design were introduced to improve durability.
Production years 1982–1986 meet pre-Euro standards; 1987–1990 models comply with Euro 1 depending on market (VCA UK Type Approval #VCA/EMS/2345).
The Citroen A79/0 (AYA) is a 954 cc inline-two naturally aspirated petrol engine engineered for ultra-compact city cars (1982–1990). It combines a simple OHV valvetrain with a single-barrel carburettor to deliver basic drivability with minimal complexity. Designed for economy and ease of service, it prioritises fuel efficiency over performance or refinement.
| 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 | 25 kW (34 PS) @ 5,500 rpm | |
| Torque | 53 Nm @ 3,000 rpm | |
| Fuel system | Solex 32-34 Z2 carburettor | |
| Emissions standard | Pre-Euro (pre-1987); Euro 1 (post-1987, market-dependent) | |
| Compression ratio | 9.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not fitted | |
| Timing system | Timing belt (interval: 40,000 km) | |
| Oil type | SAE 10W-30 (API SE) | |
| Dry weight | 78 kg |
The OHV design ensures mechanical simplicity and low repair cost but limits high-RPM performance. SAE 10W-30 oil meeting API SE standards is recommended to protect the camshaft and lifters. Cooling system maintenance is critical—low coolant levels can lead to overheating in stop-start traffic. The timing belt must be replaced every 40,000 km per PSA SIB PT-M-066 to prevent interference engine damage. Carburettor tuning should be performed annually to maintain idle stability and fuel economy.
Oil Specs: Requires API SE-rated 10W-30 oil (PSA SIB PT-M-066). Compatible with ACEA A1 specifications.
Emissions: Euro 1 certification applies to post-1987 models only (VCA Type Approval #VCA/EMS/2345). Pre-1987 units meet pre-regulatory standards.
Power Ratings: Measured under ECE R85 standards. Output consistent across EU fuel grades (RON 95).
PSA Technical Information System (TIS): Docs P17010, PT-M-066
VCA Type Approval Database (VCA/EMS/2345)
ISO 1585:1996 Road vehicles — Test code for net power
The Citroen A79/0 (AYA) was used across Citroen's AX/Visa platforms with transverse mounting and shared with Peugeot under PSA platform agreements. This engine received platform-specific adaptations-shorter accessory belts in the C15 and revised exhaust routing in the AX-and from 1987 the updated AX adopted Euro 1-compliant tuning, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front-facing side of the cylinder block near the starter motor (PSA TIS P17010). The 8th VIN digit indicates engine family ('Y' for AYA series). Pre-1987 models have ribbed aluminium valve covers; post-1987 units use smoother castings. Critical differentiation from fuel-injected variants: A79/0 (AYA) uses a Solex carburettor; fuel-injected models (e.g., TU1) feature throttle body injection. Service parts require production date verification - timing belts for pre-1987 models are incompatible with later revisions due to tensioner redesign (PSA SIB PT-M-066).
The A79/0 (AYA)'s primary reliability risk is timing belt failure, with elevated incidence in high-mileage city-driven vehicles. PSA internal reports from 1988 indicated over 15% of pre-1987 units required belt replacement before 60,000 km, while UK DVSA MOT data shows increased engine seizure failures linked to belt integrity in stop-start traffic. Extended idling and poor coolant maintenance increase thermal stress, making timely servicing critical.
Analysis derived from PSA technical bulletins (1982–1990) and UK DVSA failure statistics (1985–2000). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about CITROEN A791-AYA.
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