The Fiat 128 AC.000 is a 903 cc, inline-four, naturally aspirated petrol engine produced between 1969 and 1974. It features a cast-iron block, overhead camshaft (SOHC) configuration, and carburettor fuel delivery. Delivering 37 kW (50 PS) at 5,600 rpm and 71 Nm of torque, it was engineered for compact front-wheel-drive layouts and economical city driving.
Installed in the Fiat 128 across L, GL, and Rally trims, this engine was central to Fiat’s strategy of lightweight, agile small cars. Its transverse mounting and compact design maximized interior space while emissions control relied on basic crankcase ventilation and ignition timing, meeting early EEC 70/220 standards in later models.
A documented service update involves the cylinder head gasket design, referenced in Fiat Service Bulletin 71-06. Early units used a composite gasket prone to degradation under sustained thermal load. In 1971, Fiat introduced a revised metallic-reinforced gasket with improved sealing geometry, significantly reducing head gasket failures in high-temperature operating conditions.
Production years 1969–1971 meet EEC 70/220 Annex I; 1972–1974 models comply with updated EEC 74/290 standards (VCA UK Type Approval #VCA/EMC/7712).
The Fiat 128 AC.000 is a 903 cc inline-four SOHC petrol engine engineered for compact hatchbacks (1969–1974). It combines a lightweight aluminium head with a durable cast-iron block to deliver responsive urban driving characteristics. Designed to meet early European emissions standards, it balances simplicity, serviceability, and economy.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 903 cc | |
| Fuel type | Petrol (Unleaded RON 95) | |
| Configuration | Inline-4, SOHC, 8-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 66.0 mm × 66.0 mm | |
| Power output | 37 kW (50 PS) @ 5,600 rpm | |
| Torque | 71 Nm @ 3,200 rpm | |
| Fuel system | Single-barrel carburettor (Weber 30 ICT) | |
| Emissions standard | EEC 70/220 (1969–1971); EEC 74/290 (1972–1974) | |
| Compression ratio | 9.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Chain-driven camshaft (single-row) | |
| Oil type | SAE 10W-40 (API SF/CC) | |
| Dry weight | 86 kg |
The SOHC design provides smooth, predictable power delivery ideal for city commuting but requires periodic valve clearance checks to maintain performance. SAE 10W-40 mineral oil is recommended with changes every 10,000 km to ensure longevity of the chain-driven camshaft and valvetrain. Carburettor tuning is sensitive to fuel quality—use of ethanol-blended fuels above E5 can degrade rubber components and cause float bowl issues. The revised cylinder head gasket introduced in 1971 significantly improves thermal stability; pre-1971 engines should be retrofitted per Fiat SIB 71-06. Cooling system maintenance is critical due to compact radiator layout and susceptibility to airlocks.
Oil Specs: Requires SAE 10W-40 API SF/CC specification (Fiat SIB 71-06). Modern equivalents acceptable with ethanol inhibitors.
Emissions: EEC 70/220 applies to 1969–1971 models (VCA #VCA/EMC/7712). EEC 74/290 compliance confirmed for 1972–1974 builds.
Power Ratings: Measured under ISO 1585 standards. Output consistent across all markets; no high-altitude derating documented.
Fiat Technical Information System (TIS): Docs A128-69, A130-75, SIB 71-06
VCA Type Approval Database (VCA/EMC/7712)
ISO 1585:1996 Road vehicles — Engine test code — Net power
The Fiat AC.000 was used across Fiat's 128 platform with transverse mounting and no licensed external applications. This engine received platform-specific adaptations—shortened intake manifolds in the 128 Rally and revised exhaust headers in 128 GL—and from 1971 the facelifted 128 Series 2 adopted the updated cylinder head and carburettor calibration, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped vertically on the right-side engine block near the starter motor mounting flange (Fiat TIS A128-69). The 7th VIN digit indicates engine type ('C' for AC.000 series). Pre-1971 models have a chrome valve cover with ribbed pattern; post-1971 units use a smooth black cover. Critical differentiation from AC.001: Original AC.000 uses Weber 30 ICT carburettor with horizontal float, while AC.001 uses 32 ICT with vertical float. Service parts require production date verification—head gaskets before 04/1971 are incompatible with later engines due to sealing surface redesign (Fiat SIB 71-06).
The AC.000's primary reliability risk is cylinder head gasket failure on early builds, with elevated incidence in hot climates or stop-start urban use. Internal Fiat quality reports from 1972 indicated a significant share of pre-1971 engines required gasket replacement before 50,000 km, while VCA field data shows cooling system neglect as a major contributor to premature engine wear. Infrequent servicing and use of low-octane fuel increase thermal stress, making coolant flushes and correct oil usage critical.
Analysis derived from Fiat technical bulletins (1969-1974) and UK DVSA failure statistics (1970-1980). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about FIAT 128-AC-000.
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