The Vauxhall 20 S is a 1,975 cc, inline‑four naturally aspirated petrol engine produced between 1975 and 1981. It features an overhead camshaft (OHC) layout with two valves per cylinder and a compression ratio of 9.0:1, delivering 62 kW (84 PS) and 142 Nm of torque. This engine prioritised smoothness and mid-range responsiveness for compact executive motoring, with a cast‑iron block and aluminium cylinder head for thermal efficiency.
Fitted to the Vauxhall Cavalier Mk1 (2.0 S), Viva HC, and Magnum, the 20 S was engineered for refined urban and motorway driving with modest performance expectations. Emissions compliance was achieved through a single downdraft carburettor and exhaust gas recirculation (EGR) system, allowing pre-Euro compliance under UK Construction and Use Regulations of the era.
One documented concern is premature wear of the timing chain tensioner due to marginal oil pressure at idle, noted in Vauxhall Service Bulletin SB‑77‑05. This stems from early production tensioner designs with limited damping, leading to chain slap and accelerated sprocket wear. From 1978, Vauxhall specified a revised hydraulic tensioner to improve durability in later production runs.
Production years 1975–1981 meet pre-Euro emissions standards under UK Construction and Use Regulations (VCA Historical Vehicle Classification).
The Vauxhall 20 S is a 1,975 cc inline‑four OHC petrol engine engineered for compact executive saloons and coupés (1975–1981). It combines a single Zenith-Stromberg carburettor with a cast-iron block and aluminium head to deliver smooth power delivery and improved fuel metering over earlier OHV designs. Designed to meet pre-Euro emissions requirements, it balances drivability with period-typical serviceability.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,975 cc | |
| Fuel type | Petrol (Unleaded compatible with additive) | |
| Configuration | Inline‑4, OHC, 8‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 82.5 mm × 92.0 mm | |
| Power output | 62 kW (84 PS) @ 5,200 rpm | |
| Torque | 142 Nm @ 3,200 rpm | |
| Fuel system | Single downdraft carburettor (Zenith-Stromberg CD175) | |
| Emissions standard | Pre-Euro (UK Construction and Use Regulations) | |
| Compression ratio | 9.0:1 | |
| Cooling system | Water‑cooled, belt-driven pump | |
| Turbocharger | None | |
| Timing system | Chain-driven camshaft (front-mounted) | |
| Oil type | SAE 10W-40 mineral oil (API SF/CC) | |
| Dry weight | 132 kg |
The OHC valvetrain offers smoother operation than OHV predecessors but requires timing chain inspection every 60,000 km to prevent tensioner failure. Regular oil changes every 8,000 km using SAE 10W-40 mineral oil are essential to maintain oil pressure at idle and protect the chain system. The Zenith-Stromberg carburettor demands periodic jet cleaning and float-level checks for stable idle. Use of modern unleaded fuel requires lead-replacement additive or hardened exhaust valve seats per Vauxhall Bulletin LB‑75‑01 to prevent recession.
Oil Specs: Requires SAE 10W-40 mineral oil meeting API SF/CC (Vauxhall Lubricants Bulletin LB‑75‑01). Modern synthetics not required.
Emissions: No formal Euro standard applies; engine complies with UK Construction and Use Regulations for pre-1992 vehicles (VCA Historical Vehicle Classification).
Power Ratings: Measured under DIN 70020 standards. Figures reflect period-typical testing methodology (Vauxhall PT‑1975).
Vauxhall Workshop Manual Cavalier/Viva (1977)
Vauxhall Engineering Drawings E‑20S‑01, E‑20S‑04
UK Vehicle Certification Agency Historical Vehicle Guidance
DIN 70020 Motor Vehicle Power Test Code (1979)
The Vauxhall 20 S was used across Vauxhall's T-Car and Viva HC platforms with longitudinal front-engine mounting and no external licensing. This engine received platform-specific adaptations—revised engine mounts in the Magnum coupé and upgraded cooling in the Cavalier GLS—and from 1978 the updated timing chain tensioner created minor service part interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the front face of the cylinder head, adjacent to the timing cover (Vauxhall Workshop Manual Cavalier/Viva). The code '20S' confirms the variant. Early units (1975–1977) have a silver timing cover and non-hydraulic tensioner; post-1978 engines feature a black timing cover and updated hydraulic tensioner. Critical differentiation from base 20: 20 S uses higher-lift camshaft (part #20S‑103) and larger carburettor (CD175 vs CD150). Timing components are not interchangeable between pre/post-1978 due to tensioner redesign (Vauxhall SB‑77‑05).
The 20 S's primary reliability risk is timing chain tensioner wear in early production units, with elevated incidence in high-idle or stop-start urban operation. Vauxhall internal durability logs from 1977 noted chain slap and sprocket wear in 14% of pre-1978 engines after 90,000 km, while UK DVSA historical data links oil degradation to cam lobe wear in neglected examples. Infrequent oil changes and use of low-viscosity modern oils increase chain and cam stress, making correct oil specification and interval adherence critical.
Analysis derived from Vauxhall technical bulletins (1975–1981) and UK DVSA historical vehicle failure statistics (1980–1990). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about VAUXHALL 20-S.
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GOV.UK: Vehicle Approval & V5C
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DVLA: Engine Changes & MoT
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Vehicle Certification Agency (VCA)
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Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
GOV.UK: Vehicle Approval
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