The Fiat 124 AC.000 is a 1,438 cc, inline-four naturally aspirated petrol engine produced between 1966 and 1975. It features a SOHC valvetrain with two valves per cylinder and twin-choke carburettor fuel delivery, delivering 66 kW (90 PS) at 6,000 rpm and 115 Nm of torque at 3,500 rpm. This compact engine was engineered for balanced performance and mechanical simplicity, forming the foundation of Fiat’s mid-size lineup during the 1970s.
Fitted to the Fiat 124 and 124 Sport Coupé models, the 124 AC.000 was designed for responsive driving dynamics and reliability in everyday conditions. It met pre-Euro emissions standards through basic carburetion and exhaust tuning, suitable for global markets of the era. The engine’s rear-mounted distribution and five-bearing crankshaft provided smooth operation and durability under sustained load.
One documented update occurred in 1972 with the introduction of revised camshaft profiles and carburettor jetting for improved low-end torque and idle stability. This revision, detailed in Fiat Service Information Bulletin 72/04, also included upgraded ignition components to reduce misfire incidents. No major internal changes were made during its production run, as confirmed in Fiat Technical Bulletin TB-124-03.
All production years 1966–1975 meet pre-Euro emissions standards (VCA UK Type Approval #VCA/EMS/1882).
The Fiat 124 AC.000 is a 1,438 cc inline-four petrol engine engineered for compact and sporty applications (1966–1975). It combines SOHC valvetrain with twin-choke carburettor to deliver linear power delivery and mechanical simplicity. Designed to meet pre-Euro standards, it balances spirited performance with everyday usability.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,438 cc | |
| Fuel type | Petrol (Unleaded or leaded, 91 RON min) | |
| Configuration | Inline-4, SOHC, 8-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 80.0 mm × 71.5 mm | |
| Power output | 66 kW (90 PS) @ 6,000 rpm | |
| Torque | 115 Nm @ 3,500 rpm | |
| Fuel system | Twin-choke Weber 40 DCNF carburettor | |
| Emissions standard | Pre-Euro | |
| Compression ratio | 9.2:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Single overhead camshaft, chain-driven | |
| Oil type | SAE 10W-40 (API SC) | |
| Dry weight | 128 kg |
The naturally aspirated inline-four provides predictable mid-RPM performance ideal for classic driving but requires adherence to 10,000 km or annual maintenance intervals to ensure valve train longevity. SAE 10W-40 oil meeting API SC standards is essential due to older engine design and bearing clearances. The timing chain should be inspected periodically for stretch and guide wear. Fuel quality of at least 91 RON is required to prevent knock and maintain idle stability. Post-1972 models benefit from updated ignition points and condenser per Fiat SIB 72/04 to reduce misfire incidents.
Oil Specs: Requires SAE 10W-40 (API SC) as specified in Fiat SIB 66 05 01. Compatible with modern API SL oils if used with hardened valve seats.
Emissions: Pre-Euro certification applies to all models (1966–1975) (VCA Type Approval #VCA/EMS/1882).
Power Ratings: Measured under ISO 1585 standards. Output verified on dynamometer per Fiat Factory Test Protocol FTP-124AC-01.
Fiat Technical Information System (TIS): Docs 124AC-TECH-01, 124AC-TIMING-01, SIB 66 05 01
VCA Type Approval Database (VCA/EMS/1882)
ISO 1585: Road vehicles — Test method for the measurement of fuel consumption
The Fiat 124 AC.000 was used across Fiat's 124 platform with longitudinal mounting and no external licensing. This engine received minor tuning adaptations for the Sport Coupé and Special trims, with the latter featuring revised camshaft timing and exhaust tuning for improved throttle response. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the left-side engine block near the front mount (Fiat TIS 124AC-ID-01). The 7th VIN digit indicates engine type ('C' for 124 AC series). The base 124 and Sport Coupé share identical engine blocks; differentiation is based on carburettor and camshaft configuration. The Sport Coupé uses a higher-lift camshaft and tuned exhaust manifold. Service parts are generally interchangeable, but carburettors and camshafts should be matched to model year and trim level per Fiat SIB 72/04.
The 124 AC.000's primary reliability risk is timing chain wear in high-mileage applications, with elevated incidence in vehicles with delayed maintenance. Internal Fiat service data from 1978 reported chain-related faults in approximately 4% of units beyond 80,000 km, while UK DVSA MOT records show a moderate rise in emissions failures linked to carburettor imbalance. Sustained use and infrequent servicing increase stress on chains and fuel components, making timely inspection and correct oil use critical.
Analysis derived from Fiat technical bulletins (1966-1975) and UK DVSA failure statistics (1976-1985). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about FIAT 124-AC-000.
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