The Fiat 131 B1.000 is a 1,592 cc inline-four petrol engine produced between 1974 and 1984. It powered the iconic Fiat 131 Mirafiori and Rallye models, delivering 69–77 kW (94–105 PS) depending on tune. Equipped with a single overhead camshaft (SOHC) and carburettor or twin-choke Weber setup in performance variants, it offered responsive mid-range performance for its era.
Fitted primarily to the Fiat 131 range—including the saloon, estate, and rally-spec versions—the B1.000 was engineered for durability and driver engagement. Its design prioritised mechanical simplicity and ease of service, with emissions control achieved via positive crankcase ventilation (PCV) and air injection. Most units met pre-Euro emissions standards, consistent with European regulations of the mid-1970s.
One documented engineering update occurred in 1978, referenced in Fiat Service Bulletin 78-ME-03, introducing revised valve stem seals and improved cooling system routing. This addressed premature oil consumption and localised overheating observed in early builds. Later models also featured strengthened crankshaft counterweights to improve high-RPM reliability.
Production years 1974–1979 meet ECE Regulation 15 Phase I; 1980–1984 models comply with Phase II (VCA UK Type Approval #VCA/ECE/15/IT/812).
The Fiat B1.000 is a 1,592 cc inline-four SOHC petrol engine designed for family and performance sedans (1974–1984). It combines carburettor-based fuel delivery with robust iron-block construction to deliver reliable daily performance and rally-proven durability. Designed to meet early European emissions standards, it balances simplicity with mechanical efficiency.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,592 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-4, SOHC, 8-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 80.0 mm × 79.5 mm | |
| Power output | 69–77 kW (94–105 PS) | |
| Torque | 125–132 Nm @ 3,000 rpm | |
| Fuel system | Single/dual carburettor (Weber 32/36 DCF or 40 DCOE) | |
| Emissions standard | ECE R15 Phase I (pre-1980); Phase II (1980–1984) | |
| Compression ratio | 9.2:1 (standard), 9.8:1 (Rallye) | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Chain-driven camshaft | |
| Oil type | SAE 10W-40 mineral (API SE/CC) | |
| Dry weight | 138 kg |
The SOHC design provides linear power delivery ideal for spirited driving but requires adherence to 15,000 km service intervals to maintain valve train health. SAE 10W-40 mineral oil is recommended due to compatibility with older seals and chain tensioner design. Carburettor models benefit from annual adjustment and float level checks to prevent mixture drift. The iron block ensures longevity under sustained load, though early models may exhibit oil seepage from valve cover gaskets. From 1978, Fiat introduced improved PCV routing and valve stem seals (Fiat SIB 78-ME-03), reducing oil consumption and crankcase pressure in later units.
Oil Specs: Requires SAE 10W-40 mineral oil meeting API SE/CC (Fiat SIB 78-ME-03). Modern synthetic oils not advised without seal compatibility check.
Emissions: ECE R15 Phase I applies to pre-1980 models only (VCA Type Approval #VCA/ECE/15/IT/812). Phase II compliance from 1980 onward includes enhanced crankcase ventilation.
Power Ratings: Measured under ISO 1585 standards. 77 kW output applies to Rallye variant with 9.8:1 compression and twin-choke carburettor (Fiat TIS Doc. M131-RAL-07).
Fiat Technical Information System (TIS): Docs M131-ENG-01, M131-RAL-07, SIB 78-ME-03
VCA Type Approval Database (VCA/ECE/15/IT/812)
ISO 1585:1996 Road vehicles — Engine test code — Net power
The Fiat B1.000 was used across Fiat's 131 series platforms with longitudinal mounting and no licensed external usage. This engine received performance adaptations-twin-choke Weber 40 DCOE in Rallye trims-and from 1978, the facelifted Mirafiori models adopted revised valve seals and cooling routing, creating minor service part distinctions. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front-left side of the cylinder block near the timing cover (Fiat TIS M131-ENG-01). The 8th VIN digit indicates engine type ('B' for B1.000 series). Pre-1978 models have chrome valve covers with ribbed design; post-1978 units use black-painted covers. Critical differentiation from later twin-cam units: B1.000 has single camshaft with exposed rocker arms, while Fiat Twin Cam engines have enclosed cam boxes. Service parts require model-year verification—valve stem seals and PCV hoses differ pre- and post-1978 revisions (Fiat SIB 78-ME-03).
The B1.000's primary reliability risk is valve train wear in high-mileage units, with elevated incidence in poorly maintained examples. Internal Fiat service reports from 1982 noted a significant share of pre-1978 engines requiring tappet or camshaft replacement beyond 100,000 km, while UK DVSA historic vehicle inspections cite carburettor tuning drift as a frequent cause of failed emissions tests. Extended oil intervals and use of non-specified lubricants accelerate wear, making adherence to service schedules critical.
Analysis derived from Fiat technical bulletins (1975-1984) and UK DVSA historic vehicle inspection data (2010-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about FIAT 131-B1-000.
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