MG Midget, Known Issues and Common Problems
Overview
The MG Midget is a simple, lightweight sports car that was built to a price. The A-series engine is one of BMC’s most robust designs, the gearbox is adequate, and the electrical system is basic but functional. However, these cars are now 50—65 years old, and the combination of age, thin steel, and British manufacturing tolerances means every surviving Midget has problems to address.
The Midget’s biggest vulnerability is its body. The car is lighter and smaller than the MGB, with thinner gauge steel, and it rots with even greater enthusiasm. The second vulnerability depends on your engine: the A-series 1275 is nearly bulletproof; the Triumph 1500 has a genuine weakness in its bottom end.
Body and Structure
Sill Corrosion
What happens: The outer sill skin softens, bubbles, and crumbles. When prodded, it offers no resistance. In severe cases, the door drops when opened because the inner sill has lost its structural integrity.
Why it happens: The box-section sills trap water when drain holes block with road dirt and underseal. The corrosion works from inside out — by the time exterior rust is visible, the inner sill may be seriously compromised. The Midget’s sills are structural — they carry bending loads and are integral to the monocoque.
How to fix it: Full sill replacement — inner and outer sections. This requires stripping the affected area to bare metal, cutting out all corroded material, and welding new panels. Heritage repair panels are available and well-made. Cost: $1,200—2,500 per side.
Severity: Critical. Compromised sills make the car structurally unsafe and cause cascading problems with door alignment and body rigidity.
Floor Pan Corrosion
What happens: Soft or perforated floors, particularly in the footwells. Wet carpets after rain. In extreme cases, visible road surface through the floor.
Why it happens: Water enters through deteriorated seals and from below. The Midget’s floors are thin and close to the road. Carpet retains moisture against the steel.
How to fix it: Weld in repair sections. Available from British parts specialists. Cost: $400—1,200 per section.
Severity: Urgent. Structural and safety concern.
Rear Spring Hanger Deterioration
What happens: The rear leaf spring mounting points crack, distort, or tear away from the body under load.
Why it happens: Road spray and trapped mud corrode the metal around the spring hangers. The constant load from the springs fatigues the weakened metal.
How to fix it: Weld in new hanger assemblies. Cost: $300—700 per side.
Severity: Critical. A failed spring hanger means the rear axle is unlocated on that side. This is dangerous.
Inner Wing and Suspension Turret Corrosion
What happens: The inner front wings around the front suspension top mounts corrode and thin.
Why it happens: Road spray and trapped moisture in the double-skinned areas. The Midget’s engine bay is compact, so water doesn’t drain well.
How to fix it: Fabricate and weld repair sections. Cost: $800—2,000 per side.
Severity: Critical. These areas carry front suspension loads.
Engine — A-Series (948, 1098, 1275)
Thrust Washer Wear (Crankshaft End-Float)
What happens: A metallic knocking or clunking noise from the front of the engine, particularly when the clutch is depressed or released. The clutch may feel different — pedal travel changes, engagement point shifts.
Why it happens: The A-series engine uses thrust washers to control the crankshaft’s fore-and-aft movement (end-float). These washers wear over time, particularly on cars that spend a lot of time in traffic with the clutch partially depressed. When the thrust washers wear beyond specification, the crankshaft can move excessively, which eventually wears the rear main bearing housing and can lead to catastrophic failure.
How to fix it: Check crankshaft end-float with a dial indicator — specification is 0.05—0.13mm. Above 0.25mm is danger territory. Replacing thrust washers requires splitting the engine. If caught early, it is a straightforward repair during an engine rebuild. If left until the crank has worn the block, the repair becomes much more expensive. Cost: $100—200 for thrust washers (as part of a rebuild), $2,000—4,000 for a full engine rebuild.
Severity: Critical if end-float is excessive. This is the A-series engine’s most dangerous failure mode. Check it on every car you inspect.
Oil Leaks
What happens: Oil on the engine, oil on the ground, oil smell from the exhaust manifold.
Why it happens: Every gasket and seal on the A-series hardens and leaks with age. The rear main seal is a scroll-type design that relies on engine oil viscosity to maintain its seal — it is not a positive seal and will always weep slightly.
How to fix it: Systematic reseal. Replace all gaskets and seals. The rear main seal can only be replaced with the engine out or the gearbox removed. Full reseal: $150—300 DIY, $500—1,000 at a workshop.
Severity: Needs attention. Oil on the exhaust manifold is a fire risk.
Overheating
What happens: Temperature gauge climbs in traffic or on hot days. Coolant loss through overflow.
Why it happens: The A-series cooling system is marginal in Australian conditions. The original radiator loses capacity with age. The thermostat sticks. The water pump weeps.
How to fix it: Replace the radiator (aluminium upgrade $200—400), thermostat ($15—25), water pump ($40—80), and all hoses. Total cooling system refresh: $250—500.
Severity: Urgent. Overheating warps the cylinder head and blows head gaskets.
Engine — Triumph 1500
Crankshaft Failure
What happens: A sudden, catastrophic failure — loud metallic banging followed by engine seizure. Oil on the road. The engine is destroyed.
Why it happens: The Triumph 1500 engine has big-end bearing journals that are marginally sized for the loads they carry. Under sustained high-RPM driving, the bearing caps flex, the bearings overheat, and the crankshaft can crack or the connecting rod can let go. The problem is exacerbated by low oil pressure, overheating, or insufficient oil changes.
How to fix it: Prevention is the only real fix. Keep the oil fresh (change every 5,000 km), avoid sustained high-RPM running, monitor oil pressure, and ensure the cooling system is in excellent condition. If the crank fails, the engine is typically beyond economic repair — a replacement engine ($800—1,500 used) is cheaper than rebuilding the broken one.
Severity: Critical potential. Not every 1500 will fail, but the risk is real. Treat the engine with respect.
1500 Overheating
What happens: Persistent overheating, particularly in traffic.
Why it happens: The 1500 engine runs hotter than the A-series, and the Midget’s cooling system was designed for the smaller, cooler-running engine. The radiator is barely adequate.
How to fix it: Aluminium radiator upgrade, new thermostat, new water pump. Consider an electric fan upgrade. Cost: $300—600.
Severity: Critical. Overheating accelerates the crankshaft failure risk described above.
Gearbox
Second Gear Synchro Wear
What happens: Crunching or grinding when downshifting quickly from 3rd to 2nd, especially when cold.
Why it happens: Second gear synchro takes the most punishment in normal driving. The brass synchro ring wears thin and cannot match shaft speeds.
How to fix it: Gearbox rebuild with new synchro rings. Cost: $600—1,200 for a rebuild. A used replacement gearbox is $300—600.
Severity: Needs attention. Double-clutching on downshifts extends synchro life.
Suspension
Leaf Spring Fatigue and Axle Tramp
What happens: The rear of the car sags. Under hard cornering on bumpy surfaces, the rear axle hops (tramping) — a disconcerting and potentially dangerous loss of traction.
Why it happens: The leaf springs lose their temper over decades, reducing ride height and spring rate. Axle tramp is inherent to the live-axle-on-leaf-spring layout, but it is worsened by worn springs and dampers.
How to fix it: Replace the leaf springs — standard or parabolic upgrade. Fit telescopic shock absorbers in place of the original lever-arm dampers (conversion kits: $150—300). The parabolic spring conversion ($400—700 per set) dramatically improves ride quality and reduces tramp.
Severity: Needs attention. Sagging springs affect handling and ground clearance. Axle tramp can cause loss of control.
Front Suspension Wear
What happens: Clunking from the front end, wandering on straight roads, uneven tyre wear.
Why it happens: The Midget’s front suspension uses coil springs and wishbones with kingpins (early) or ball joints (late). Bushings perish, kingpin bushings wear, and ball joints develop play.
How to fix it: Replace worn bushings, kingpins, or ball joints. Front suspension rebuild kit: $200—400.
Severity: Needs attention. Worn front suspension makes the car vague and unsafe.
Electrical
Lucas Electrical Failures
What happens: Intermittent lights, dead instruments, no-start conditions, blown fuses.
Why it happens: The Lucas electrical system relies on ageing wire insulation, corroded connectors, and poor earth connections. After 50+ years, the wiring harness insulation is brittle and earth points are corroded.
How to fix it: Clean all earth connections. Inspect and repair damaged wiring. A full replacement wiring harness ($400—800) is the ultimate solution. Electronic ignition conversion ($80—150) eliminates the most common ignition failure modes.
Severity: Needs attention. Electrical fires are a real risk with deteriorated wiring.
Dynamo/Alternator Failure
What happens: Battery goes flat, charging light stays on, dim lights.
Why it happens: Early Midgets use a dynamo (generator) that is less efficient than an alternator. Both types suffer from worn brushes and failed regulators after 50 years.
How to fix it: Convert to an alternator (if still on a dynamo) or replace the alternator. Cost: $100—250.
Severity: Needs attention. A dead charging system strands you.
Cooling and Fuel
SU Carburettor Wear
What happens: Rough idle, poor throttle response, rich or lean running.
Why it happens: The twin SU carburettors develop throttle shaft bushing wear (causing air leaks), needle and jet wear, and perished diaphragms.
How to fix it: Service with new needles, jets, and gaskets ($25—40 per carburettor). Rebush throttle shafts if worn ($40—80 per carburettor).
Severity: Needs attention. Poorly set carburettors waste fuel and reduce driveability.
Fuel Pump Failure (SU Electric)
What happens: Engine starves for fuel, particularly under load or with a low fuel tank.
Why it happens: The SU electric fuel pump’s contact points corrode and pit. The diaphragm perishes with age and ethanol exposure.
How to fix it: Rebuild ($30—60) or replace with a modern solid-state pump ($60—120).
Severity: Needs attention. Carry a small hammer — tapping the pump body can restore contact temporarily.
Hood and Weather Equipment
Hood Deterioration
What happens: Cracked vinyl, torn seams, broken press studs, persistent leaks.
Why it happens: Australian UV destroys vinyl and fabric. The hood frame fatigues and distorts. Press studs corrode and pull through the material.
How to fix it: Replacement hoods: $300—600 (vinyl) or $500—900 (mohair). A new hood transforms the car’s appearance and liveability.
Severity: Cosmetic but affects usability. A leaking hood makes the car impractical and accelerates interior rust.
Preventive Maintenance
- Check crankshaft end-float on every A-series engine — annually or at purchase. This is the most critical preventive check.
- Inspect for rust every 12 months. Sills, floors, spring hangers, inner wings.
- Maintain the cooling system. Upgrade the radiator, fresh hoses, correct thermostat.
- Grease kingpins (early cars) every 5,000 km.
- Fit electronic ignition. Eliminates the most common breakdown cause for under $100.
- Check and clean earth connections annually.
- Change oil every 5,000 km with 20W-50 mineral oil.
- If you own a 1500: Treat the engine gently, change oil religiously, and monitor oil pressure.
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