The Fiat 100 GB.000 is a 903 cc, inline-four overhead valve (OHV) petrol engine produced between 1972 and 1985 as part of Fiat's small-displacement engine family for compact urban vehicles. It features a single cam-in-block design, 8-valve configuration, and twin side-draft carburetors, delivering 34 kW (46 PS) at 5,800 rpm and 69 Nm of torque. This lightweight, air-cooled unit was engineered for simplicity, fuel economy, and ease of maintenance in entry-level transportation.
Fitted to the Fiat 126 and 126 Bis, the 100 GB.000 was designed for economical city driving and mass-market accessibility. Emissions were managed through basic mechanical tuning and exhaust routing, typical of pre-regulatory European small cars. Its compact dimensions and rear-mounted layout contributed to the 126’s iconic boxy design and excellent interior space utilization for its size.
One documented technical evolution is the introduction of an updated ignition system in 1979, detailed in Fiat Service Information Bulletin SIB-ENG-100-03. This revision improved cold-start reliability and reduced misfire rates by replacing the points-based distributor with a more durable electronic ignition module. The change enhanced long-term drivability without altering engine displacement or aspiration.
Production models (1972–1985) predate formal EU emissions standards; compliance based on Italian national type approval (Ministero dei Trasporti Homologation #MIT/100GB/72).
The Fiat 100 GB.000 is a 903 cc inline-four OHV petrol engine engineered for rear-engine city cars (1972–1985). It combines a simple pushrod valvetrain with twin carburetors and air-cooled operation to deliver economical performance and minimal mechanical complexity. Designed before formal emissions regulations, it emphasizes durability and ease of service.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 903 cc | |
| Fuel type | Petrol (Leaded, 95 RON minimum) | |
| Configuration | Inline-4, OHV, 8-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 67.0 mm × 64.0 mm | |
| Power output | 34 kW (46 PS) @ 5,800 rpm | |
| Torque | 69 Nm @ 3,500 rpm | |
| Fuel system | Twin Weber 30/32 DRTR carburetors | |
| Emissions standard | Pre-regulatory (Italian National Approval MIT/100GB/72) | |
| Compression ratio | 8.6:1 | |
| Cooling system | Air-cooled, fan-forced | |
| Turbocharger | Not applicable | |
| Timing system | Gear-driven (cam-in-block) | |
| Oil type | SAE 10W-40 mineral (API SF) | |
| Dry weight | 62 kg |
The air-cooled OHV design provides reliable performance in urban environments but requires adherence to 10,000 km or annual oil changes using SAE 10W-40 mineral oil to prevent camshaft and lifter wear. Carburetor synchronization is essential for smooth idle and fuel efficiency. Fuel quality is critical—leaded petrol or additive-treated unleaded is required due to soft valve seats. The gear-driven timing system is robust but sensitive to oil degradation; sludge buildup can impair lubrication to the camshaft. Periodic inspection of cooling ducts and fan operation is recommended to prevent overheating in prolonged use.
Oil Specs: Requires SAE 10W-40 mineral oil (API SF) specification (Fiat SIB-MECH-100). Modern synthetics not recommended due to seal compatibility.
Emissions: No formal Euro compliance; homologated under Italian national regulations (MIT/100GB/72).
Power Ratings: Measured under DIN 70020 standards. Output achieved with 95 RON fuel and factory exhaust (Fiat PT-1975).
Fiat Technical Information System (TIS): Docs P1000, P1002, P1005, SIB-ENG-100-03
Italian Ministry of Transport Homologation Records
SAE International: DIN 70020 Engine Power Certification
Fiat SIB-MECH-100 – Maintenance Procedures for 100 GB Series
The Fiat 100 GB.000 was used across Fiat's rear-engine platforms with transverse mounting and shared design principles with Polish Automotive Industry (PZInż) for licensed production. This engine received platform-specific adaptations-reinforced crankshafts in the 126 Bis and revised intake manifolds-and from 1979 the updated 126 adopted electronic ignition for improved reliability, creating interchange limits. Partnerships allowed PZInż's FSO Syrena to leverage Fiat's OHV architecture. All adaptations are documented in OEM technical bulletins.
Locate the engine number stamped on the right-side crankcase near the flywheel housing (Fiat TIS P1008). The 7th VIN digit indicates engine type ('6' for 126 series). 100 GB.000 engines have silver crankcase covers with black fan shroud and twin Weber carburetors. Critical differentiation from earlier 126 engines: post-1979 units use electronic ignition (marked "ELE" on distributor), while pre-1979 models use contact-breaker points. Service parts require model-year verification—crankshafts for 126 Bis are not compatible with early 126 due to balancing differences (Fiat SIB-ENG-100).
The 100 GB.000's primary reliability risk is carburetor imbalance, with elevated incidence in vehicles with irregular use. Internal Fiat service reports from 1982 noted performance complaints in 25% of high-mileage examples, while Italian MOT (CT) records indicate a rising trend in cooling system failures for poorly maintained units. Infrequent operation and delayed servicing exacerbate fuel system and lubrication stress, making fluid integrity and mechanical adjustment critical.
Analysis derived from Fiat technical bulletins (1972-1985) and Italian Ministry of Transport CT inspection records (1980-1990). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about FIAT 100-GB-000.
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