Cosmo Sport (110S)
1967-1972 / Coupe / Japan
The Cosmo Sport was Mazda's statement of intent: a beautiful sports coupe powered by the world's first mass-produced twin-rotor Wankel engine. Where other manufacturers had tried and failed to make the rotary engine work reliably, Mazda succeeded through sheer determination and engineering brilliance. Only 1,519 were built, making it one of the rarest Japanese classics in existence.
The 110S designation refers to its 110hp output, which was impressive for a car of its size and weight. The Cosmo established Mazda's rotary identity that would define the brand for decades, leading directly to the RX series that followed. Australian examples are extraordinarily rare and command high prices when they surface. The Cosmo is the genesis car for every rotary enthusiast, the car that proved the Wankel engine could power a proper sports car and not just a curiosity.
Thinking of buying a Cosmo Sport (110S)?
What to look for, what to pay, what to avoid.
What to watch for.
Apex Seal Wear
Minor Engine, 10A Twin-Rotor (982cc)
Apex Seal Wear
MinorLoss of compression, reduced power, difficulty starting (especially when cold), blue-white exhaust smoke, and eventually misfiring and inability to idle. A rotary engine with worn apex seals is an engine that needs a rebuild, there is no halfway measure.
The apex seals are the rotary equivalent of piston rings. They ride on the tips of the triangular rotor, sealing the combustion chamber against the epitrochoid housing. The 10A was Mazda's first production rotary, and the seal materials and housing coatings were first-generation technology. The seals are narrower than those used in the later 12A and 13B, and the housing surface treatments are less durable. Wear is inevitable, the question is how many kilometres the seals last before compression drops below usable levels.
Full engine rebuild with new apex seals, side seals, corner seals, and O-rings. The housings must be inspected for scoring, if the chrome plating is damaged, the housings need re-plating (a specialist process available from a small number of firms worldwide). An engine rebuild by a rotary specialist in Australia (Atkins Rotary, PAC Performance, or Promaz) will cost $5,000-10,000+ depending on housing condition. Sourcing 10A-specific parts may add to this cost significantly.
Hard Cold Starting
Common Engine, 10A Twin-Rotor (982cc)
Hard Cold Starting
CommonThe engine cranks extensively before firing when cold. May require multiple attempts. Once warm, starting is normal.
Multiple factors combine. The 10A's apex seals contract when cold, reducing compression below the threshold needed for reliable ignition. The manual choke system requires precise operator technique. The ignition system (points and condenser in original specification) may be weak. The fuel system (carburettor) may not be delivering an adequately rich mixture for cold starting. And after 50+ years, every component in the fuel and ignition chain has degraded.
Systematic approach: verify compression first (if compression is low, no amount of ignition or fuel work will fix starting). Clean or rebuild the carburettor. Replace points and condenser (or convert to electronic ignition, a common and reversible modification). Ensure the choke mechanism is functioning correctly. Verify the starting enrichment circuit. Many owners install a small electric fuel pump to ensure the carburettor bowls are full before cranking.
Oil Metering Pump Failure
Minor Engine, 10A Twin-Rotor (982cc)
Oil Metering Pump Failure
MinorWithout lubrication, the apex seals run metal-on-metal against the rotor housing. Wear accelerates catastrophically. The engine may seize.
The oil metering pump (OMP) injects small quantities of two-stroke oil directly into the combustion chamber to lubricate the apex seals. The pump is mechanical, driven by the engine. After 50+ years, the pump's internal seals can fail, the delivery lines can crack or clog, and the pump itself can seize. Some previous owners may have disconnected the pump and switched to premix (adding oil directly to the fuel), which works but requires discipline, forget to premix and the engine is destroyed.
If the OMP is original and functioning, maintain it. Replace the delivery lines with new silicone hose. If the pump is not functioning, either rebuild it (parts are scarce) or commit to premix operation at 1:200 ratio. If running premix, label the fuel filler prominently and never let anyone else fuel the car without instruction.
Cooling System Inadequacy
Critical Engine, 10A Twin-Rotor (982cc)
Cooling System Inadequacy
CriticalEngine overheating, particularly in traffic or on hot days. The temperature gauge climbs steadily, coolant may boil over, and in extreme cases the engine suffers heat-related damage (warped housings, blown coolant seals).
Rotary engines generate more waste heat than reciprocating engines of equivalent power. The Cosmo Sport's cooling system was designed for 1960s Japanese conditions and 1960s driving patterns (lower speeds, cooler ambient temperatures). In Australian summer conditions, the original radiator, water pump, and fan setup are marginal. After 50+ years of corrosion and degradation, they are often inadequate.
Flush and inspect the entire cooling system. Replace the thermostat. Consider an upgraded aluminium radiator (available from specialist fabricators, there is no off-the-shelf item for the Cosmo Sport). Ensure the water pump is functioning efficiently. An electric fan conversion can provide better airflow at low speeds than the mechanical fan. Always use quality coolant at the correct concentration.
Points and Condenser Degradation
Common Ignition System
Points and Condenser Degradation
CommonMisfiring, rough running, difficulty starting, inconsistent idle.
The original ignition system uses contact breaker points and a condenser. These are wear items that require regular adjustment and replacement, something that was routine maintenance in the 1960s but is often neglected today. The points pit and corrode, the condenser fails, and the spark becomes weak and inconsistent.
Replace points and condenser as a starting point. For reliability, many owners fit an electronic ignition module (Pertronix or similar) inside the original distributor housing. This is invisible from the outside, fully reversible, and eliminates the need for points adjustment. Cost: $100-200 for a Pertronix kit.
Spark Plug Fouling
Minor Ignition System
Spark Plug Fouling
MinorMisfiring, rough idle, loss of power. Plugs come out with heavy carbon or oil deposits.
Rotary engines are harder on spark plugs than reciprocating engines. The combustion chamber sweeps past the plug, and the plug tip is exposed to the oil that lubricates the apex seals. Short trips and cold running exacerbate fouling. The 10A's relatively low compression (by modern standards) means incomplete combustion is more likely.
Use the correct spark plug (NGK BP6ES or equivalent, check a Cosmo Sport-specific reference). Replace plugs at shorter intervals than you would for a piston engine, every 10,000-15,000 km. Ensure the oil metering pump is not over-delivering. A hotter plug grade may help if the car is used for short trips.
Join the conversation.
Common questions.
What is the Mazda Cosmo Sport 110S?
The Cosmo Sport 110S is the world's first production twin-rotor car, manufactured by Toyo Kogyo (now Mazda) from 1967 to 1972 in Hiroshima, Japan. It was powered by the 10A twin-rotor Wankel engine displacing 982cc, producing either 110hp (Series I, L10A) or 128hp (Series II, L10B).
What is the difference between Series I and Series II?
The two series are visually and mechanically distinct: **Series I (L10A, 1967-1968):** - 110hp 10A engine - Four-speed manual gearbox - Shorter wheelbase (2,200 mm) - Lower, more compact body - Distinctive split rear window - 343 built - The purist's choice, rarer, more historically significant **Series II (L10B, 1968-1972):** - 128hp 10A engine (revised porting and compression) - Five-speed manual gearbox - Longer wheelbase (2,350 mm) - Larger body with more interior space - Single-piece rear window - 833 built - More usable, slightly more available The Series I is generally more valuable due to its rarity and its status as the first of the breed. However, the Series II is the better car to drive, with more power, an extra gear, and improved refinement.
How much is a Cosmo Sport worth in Australia?
Prices depend entirely on condition and provenance: - **Restoration project (complete, needs everything):** $100,000-180,000 AUD - **Running, presentable condition:** $150,000-300,000 AUD - **Concours restored:** $250,000-450,000+ AUD Series I cars command a premium over Series II. Documented history, matching numbers, and known provenance add significant value.
Was the Cosmo Sport sold in Australia?
No. The Cosmo Sport was sold exclusively in Japan.
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