MGA, Known Issues and Common Problems
Overview
The MGA (1955-1962) is a well-engineered sports car built around proven BMC components. The B-series engine is one of the most successful and durable engines of its era, the gearbox is robust, and the chassis is straightforward. The MGA’s problems are primarily age-related, after sixty-plus years, every rubber component, every seal, and every piece of steel has been subjected to decades of deterioration.
The good news is that the MGA is exceptionally well-supported. Every component is available as a new or remanufactured part, the enthusiast community has documented every repair procedure, and any competent British car specialist can work on these cars blindfolded. The problems below are patterns, not certainties, but a high-mileage, poorly maintained MGA will have most of them.
Rust
Sill (Rocker Panel) Corrosion
What happens: The sills become soft, bubbly, or perforated. The body may flex excessively when jacked up or driven over bumps. Doors may not shut properly as the body distorts.
Why it happens: The MGA’s sills are box-section steel that traps moisture from road spray, condensation, and water ingress through the body seams. Rust starts inside and works outward, by the time it’s visible on the surface, the internal structure is compromised. Blocked drain holes accelerate the problem.
How to fix it: Cut out the corroded section and weld in a repair panel (or a complete replacement sill). The sills are structural, so the repair must be done properly, pop-riveted patches and filler are not acceptable. Repair panels are available from Moss Motors, SC Parts, and other suppliers. Cost: $500-$1,500 per side for supply and professional fitting.
Severity: Critical. The sills are load-bearing elements. Corroded sills compromise the body’s integrity and affect handling and safety.
Floor Pan Corrosion
What happens: Soft or perforated metal in the floor pans, visible from underneath. Water may pool in the footwells. The floor may flex under foot pressure.
Why it happens: Water enters through deteriorated body seals, leaking weather equipment, and condensation. The flat floor pans offer no drainage, so water sits and rusts through the steel.
How to fix it: Cut out corroded sections and weld in repair panels. Complete floor pan assemblies are available. Cost: $300-$600 per side for panels, plus fitting.
Severity: Needs attention. While not as immediately structural as the sills, corroded floor pans indicate water ingress that’s likely affecting other areas too.
Front Crossmember Corrosion
What happens: Visible rust, scaling, or perforation of the front crossmember (visible from underneath the front of the car).
Why it happens: Road spray, mud, and trapped moisture attack the crossmember. It’s a hidden area that’s easy to overlook during casual inspections.
How to fix it: If surface rust only, clean, treat with rust converter, and protect. If structurally compromised, the crossmember must be replaced, this is a major job requiring the front end to be disassembled. Cost: $1,000-$3,000 for replacement.
Severity: Critical. The front crossmember supports the engine and front suspension. Failure is catastrophic.
Rear Spring Hanger Corrosion
What happens: The rear spring mounting points show rust, cracking, or distortion. The rear of the car may sit unevenly or make clunking noises.
Why it happens: Road spray attacks the spring hanger brackets and the surrounding bodywork. The stress of the spring loading concentrates corrosion damage.
How to fix it: Weld in new spring hanger brackets and reinforce the surrounding body metal. Cost: $500-$1,500 per side.
Severity: Critical. A failed spring hanger allows the rear axle to shift unpredictably.
Engine, BMC B-Series (1,489cc / 1,588cc)
Oil Leaks
What happens: Oil weeps from the rocker cover gasket, timing cover, rear main seal, and sump gasket. A layer of oil covers the engine and transmission.
Why it happens: Cork and rubber gaskets deteriorate over decades. The B-series rear main seal is a scroll-type design (early engines) or a lip seal (later engines), both leak eventually. The rocker cover uses a cork gasket that compresses and loses its seal with repeated removal.
How to fix it: Replace all gaskets systematically. Use modern gasket materials where possible. The rear main seal requires the engine or gearbox to be removed. A complete engine reseal: $300-$600 in parts, $500-$1,000 in labour if paying a workshop.
Severity: Needs attention. Oil on the exhaust manifold creates a fire risk and a smell. Low oil level from persistent leaks damages bearings.
Carburettor Wear (SU H4)
What happens: Rough idle, poor fuel economy, hesitation on acceleration, black smoke from the exhaust. The engine may run rich or lean depending on which component has worn.
Why it happens: The SU H4 carburettors use a throttle shaft that rotates in the carburettor body. Over decades, the shaft wears the bore oval, allowing unmetered air to enter. The jet and needle also wear, affecting mixture control. The dashpot piston and suction chamber can wear, affecting the carburettor’s response to throttle changes.
How to fix it: Rebuild the carburettors with new jets, needles, gaskets, and throttle shaft bushes. Throttle shaft rebushing requires removing the carbs and having the work done by a specialist, the bodies need reaming and new bushes pressing in. Cost: $80-$150 per carb for basic rebuild kits; $150-$300 per carb for complete rebuild including shaft rebushing.
Severity: Needs attention. Worn carburettors waste fuel, reduce performance, and can cause the engine to run dangerously lean at high RPM.
Head Gasket Failure
What happens: Coolant loss without visible external leak. White smoke from the exhaust. Milky emulsion under the oil filler cap. Overheating. Bubbles in the header tank.
Why it happens: The B-series engine uses a cast-iron block and aluminium head, different thermal expansion rates stress the head gasket. Overheating events are the primary cause of failure. Low coolant level, a stuck thermostat, or a failing water pump can all trigger overheating.
How to fix it: Remove the head, inspect and resurface if warped, replace the gasket. Check the head for cracks (particularly between valve seats). Cost: $800-$1,500 at a workshop.
Severity: Urgent. Continued driving with a blown head gasket risks hydrolock and catastrophic engine damage.
Timing Chain Stretch
What happens: A rattling noise from the front of the engine at idle. Valve timing wanders, reducing power and efficiency.
Why it happens: The single-row timing chain stretches with mileage. The tensioner compensates for some wear, but eventually the chain exceeds the tensioner’s range.
How to fix it: Replace the timing chain, tensioner, and sprockets. The timing cover must be removed. Cost: $200-$400 in parts.
Severity: Needs attention. A severely stretched chain can jump a tooth, causing valve damage.
Engine, Twin Cam (DOHC 1,588cc)
Piston and Bore Damage
What happens: High oil consumption, blue smoke from the exhaust, loss of compression. In severe cases, complete piston failure.
Why it happens: The Twin Cam engine’s high compression ratio (9.9:1) and tendency to pre-ignite on poor-quality fuel causes piston crown erosion and bore scoring. Early engines were particularly prone, the combination of high compression, inadequate fuel quality, and owner ignorance about fuel octane requirements destroyed many engines.
How to fix it: Rebore and fit new pistons (lower compression pistons are available for improved reliability). A complete Twin Cam engine rebuild is a specialist job. Cost: $5,000-$10,000.
Severity: Critical if symptoms are present. The Twin Cam engine requires specific knowledge and premium fuel.
Oil Consumption
What happens: The Twin Cam consumes oil at a rate that seems alarming to anyone accustomed to modern engines. Topping up between services is normal.
Why it happens: The DOHC head’s valve stem seals and the engine’s breathing characteristics lead to oil consumption. Some is inherent to the design; excessive consumption indicates worn valve guides or piston rings.
How to fix it: If consumption exceeds 1 litre per 1,500 km, investigate valve stem seals and piston ring condition. Valve guide replacement and ring replacement require engine disassembly. Cost: $3,000-$8,000 depending on extent.
Severity: Monitor closely. Carry spare oil and check level before every drive.
Electrical (Lucas)
Dynamo Undercharging
What happens: The charge warning light stays on or flickers. Battery goes flat. Headlights dim at idle.
Why it happens: Worn brushes, a dirty commutator, or a failed voltage regulator. The dynamo’s output is limited, approximately 22 amps, and marginal for cars with upgraded lighting or accessories.
How to fix it: Rebuild the dynamo ($200-$400) or convert to an alternator in a dynamo-style housing ($400-$600). The alternator conversion is the better long-term solution.
Severity: Needs attention. A non-charging dynamo means you’re running on battery until it dies.
Wiring Degradation
What happens: Intermittent electrical faults. Lights flicker. Gauges read erratically. Fuses blow without apparent cause.
Why it happens: Original wiring insulation becomes brittle and cracks, exposing bare copper that shorts to ground. Earth connections corrode. Bullet connectors lose contact.
How to fix it: Replace the entire wiring harness. Complete reproduction harnesses cost $300-$500 and are a weekend installation job. Cost: $300-$500 for the harness.
Severity: Needs attention. Electrical shorts in a car with fuel lines nearby present a fire risk.
Suspension and Steering
Wheel Bearing Wear
What happens: A rumbling or grinding noise from a wheel, increasing with speed. Play detectable when rocking the wheel at 12 and 6 o’clock with the car jacked up.
Why it happens: The front wheel bearings are tapered roller bearings that wear with mileage. Lack of regular greasing accelerates the process. Water ingress past failed seals causes corrosion of the bearing surfaces.
How to fix it: Replace the bearings. This is a straightforward job that requires removing the hub. Cost: $100-$200 per side for parts.
Severity: Needs attention. A failing wheel bearing can seize, with obvious consequences.
Leaf Spring Sag
What happens: The rear of the car sits lower than normal. The ride becomes harsh. The car bottoms out over bumps.
Why it happens: The rear leaf springs lose their camber over sixty-plus years. Individual leaves can also break, reducing the spring’s load-carrying capacity.
How to fix it: Re-temper and re-camber the springs, or fit new replacement springs. Cost: $300-$600 per pair.
Severity: Needs attention. Sagging springs affect handling, ride height, and ground clearance.
Kingpin Wear
What happens: Vague steering, front-end wander, uneven tyre wear.
Why it happens: The MGA’s front suspension uses kingpins (on early cars) or ball joints that wear with mileage and lack of greasing.
How to fix it: Replace kingpin bushes or ball joints as applicable. Kingpin kits: $150-$300 per side.
Severity: Needs attention for handling and safety.
Cooling System
Radiator Inefficiency
What happens: Overheating in traffic or on hot days. Temperature gauge climbs above normal.
Why it happens: The original radiator’s capacity is marginal for Australian conditions. Core tubes block with scale and corrosion over time, reducing cooling efficiency. The original thermostat may be stuck or incorrect.
How to fix it: Flush the radiator and cooling system. If the radiator is severely blocked, have it re-cored with a higher-efficiency core. Check and replace the thermostat. An electric fan behind the radiator is a common upgrade. Cost: $200-$600 depending on what’s needed.
Severity: Urgent. Overheating is the primary cause of head gasket failure and can warp the cylinder head.
Preventive Maintenance
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Inspect for rust every 12 months. Get underneath the car and check sills, floor pans, crossmember, and spring hangers. Early detection saves thousands.
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Change engine oil every 5,000 km or 6 months using 20W-50 mineral oil. The B-series thrives on regular oil changes.
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Grease the chassis at every service. Front suspension, steering, and wheel bearings all require regular lubrication.
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Check coolant level and condition regularly. Use a quality corrosion inhibitor. The B-series block is iron and the head is aluminium, galvanic corrosion is a real risk with neglected coolant.
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Service the carburettors annually. Check dashpot oil level, clean the air filters, and tune the mixture. Well-tuned SUs are reliable and efficient. Neglected SUs are neither.
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Check brake fluid level and condition every 12 months. Flush and replace every 2 years. Brake fluid absorbs moisture, which corrodes wheel cylinders from the inside.
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Inspect the hood and sidescreens (roadster) or window seals (coupe) for leaks. Water ingress is the root cause of most bodywork rust.
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