R100 (Familia Rotary)
1968-1973 / Coupe / Japan
The R100 was Mazda's first mass-market rotary car, taking the Wankel engine from the exotic Cosmo Sport and putting it in the compact Familia body. The result was a lightweight coupe with a high-revving engine that punched well above its weight class. The 10A rotary engine produced 100hp, which doesn't sound like much until you consider the car weighed less than 850kg.
In Australia, the R100 was a competitive force in motorsport, demonstrating the rotary engine's potential before the RX-3 took over. The car's combination of light weight and willing engine made it a natural for racing, and many were campaigned hard. Survivors are rare, and unmolested examples are rarer still. The R100 is an important car in Mazda's rotary history, bridging the gap between the handbuilt Cosmo and the mass-market success of the RX series.
Thinking of buying a R100 (Familia Rotary)?
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
MinorGradual loss of compression, resulting in reduced power, increasingly difficult cold starts, blue-white exhaust smoke (burning oil), and eventually rough idle, misfiring, and inability to maintain running at low RPM.
The 10A uses 2mm-wide apex seals, the narrowest of any production Mazda rotary. These seals ride on the tips of each triangular rotor, pressed against the epitrochoid housing by spring tension and combustion gas pressure. The seal material and the housing surface coating were first-generation technology. Wear is accelerated by inadequate lubrication (failed oil metering pump), overheating, cold starting with extended cranking, and short-trip driving that never allows the engine to fully warm up.
Full engine disassembly and rebuild. New apex seals, side seals, corner seals, and all O-rings. Housings must be inspected for scoring, if the chrome coating is damaged, the housings need replating (a specialist process). A 10A rebuild at a rotary specialist costs $4,000-8,000 depending on housing condition. Parts availability for the 10A is tighter than for the 12A or 13B, so allow extra time for sourcing.
Oil Metering Pump Failure
Minor Engine, 10A Twin-Rotor (982cc)
Oil Metering Pump Failure
MinorThe apex seals lose their lubrication source. Wear accelerates dramatically, and the engine may seize if run for extended periods without lubrication.
The mechanical oil metering pump (OMP) injects two-stroke oil into the combustion chambers. After 50 years, the pump's internal seals deteriorate, the delivery lines crack or clog, and the pump may lose prime. Some owners have disconnected the pump and switched to premix, this works but requires religious discipline with oil-to-fuel ratios.
Inspect the OMP and its delivery lines at every service. Replace cracked or hardened silicone delivery lines. If the pump is not salvageable, commit to premix at 1:200 ratio. If premixing, label the fuel filler cap and document the procedure so future owners (or anyone who borrows the car) cannot accidentally run the engine without oil.
Cooling System Inadequacy
Critical Engine, 10A Twin-Rotor (982cc)
Cooling System Inadequacy
CriticalThe engine overheats, particularly in traffic, on hot days, or under sustained load. The temperature gauge climbs, coolant may boil over, and the engine suffers heat distortion or blown coolant seals.
The 10A produces substantial waste heat relative to its displacement. The R100's original cooling system, a single-row brass radiator, mechanical fan, and period water pump, was adequate for 1960s Japanese conditions. In Australian summer traffic, it is marginal. After 50 years of corrosion and degradation, it is often inadequate.
Upgrade to an aluminium radiator (custom fabrication required, no off-the-shelf option). Fit an electric fan with a temperature-controlled relay. Replace the thermostat. Replace all hoses. Ensure the water pump is functioning and its seal is intact. Use quality coolant at the correct concentration.
Exhaust Port Gasket Leaks
Common Engine, 10A Twin-Rotor (982cc)
Exhaust Port Gasket Leaks
CommonExhaust gas leaks at the junction between the exhaust manifold and the engine's exhaust ports. Audible ticking sound that increases with RPM. May cause exhaust fumes in the cabin.
The exhaust port gaskets deteriorate from heat cycling. The studs that hold the exhaust manifold may also stretch or corrode, reducing clamping force.
Replace exhaust port gaskets and inspect studs. If studs are corroded or stretched, replace them. Use anti-seize compound on assembly. Cost: $30-60 for gaskets; $100-200 if studs need replacement.
Carburettor Deterioration
Common Fuel System
Carburettor Deterioration
CommonPoor idle quality, flat spots during acceleration, hesitation off idle, fuel leaks from the carburettor body, flooding, or lean running.
The R100's carburettor (typically a Hitachi or Nikki unit) has internal gaskets, needle valves, diaphragms, and float mechanisms that degrade over 50 years. Ethanol-blended fuels accelerate the deterioration of rubber components.
Complete carburettor rebuild. Kits are still available through Japanese parts suppliers and some Australian rotary specialists. Ultrasonic cleaning of the body is recommended. Replacement carburettors from donor cars may be available. Some owners convert to a Weber DCOE sidedraft setup for improved performance, this works well but sacrifices originality.
Fuel Tank Corrosion
Common Fuel System
Fuel Tank Corrosion
CommonRestricted fuel flow, debris in the fuel system, fuel leaks from the tank.
Internal corrosion of the steel fuel tank, accelerated by water contamination and ethanol-blended fuels. Rust particles from the tank circulate through the fuel system, clogging the carburettor and causing lean spots.
Remove, inspect, and seal the tank (POR-15 or Kreem tank sealer). Install an inline fuel filter between the tank and carburettor. Replace corroded fuel lines with ethanol-compatible hose and fittings. Cost: $200-500 for tank restoration; $50-100 for lines and filter.
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Common questions.
What is the Mazda R100?
The R100 is the export name for the Mazda Familia Rotary Coupe, produced from 1968 to 1973. It was the first mass-market car to use Mazda's 10A twin-rotor Wankel engine, the same fundamental engine type as the Cosmo Sport, but in an affordable, lightweight coupe body.
What engine does the R100 have?
The R100 uses the Mazda 10A twin-rotor Wankel engine. Key specifications: - **Displacement:** 982cc (491cc per rotor chamber) - **Configuration:** Twin-rotor, peripheral exhaust ports - **Power:** Approximately 100-110 hp (73-81 kW) at 7,000 rpm - **Torque:** Approximately 130 Nm at 3,500 rpm - **Fuel system:** Single carburettor (Hitachi or Nikki) - **Redline:** 7,000 rpm The 10A is the smallest and earliest production twin-rotor Mazda engine.
Did the R100 really race at Bathurst?
Yes, and that is central to its significance. In 1969, Mazda Australia entered a team of R100 coupes in the Hardie Ferodo 500 at Mount Panorama.
How many R100s were sold in Australia?
Exact Australian sales figures are difficult to confirm, but the R100 was sold in modest numbers, likely in the low thousands across its 1969-1973 Australian sales period. It was a niche product in a market dominated by the Holden Torana, Ford Cortina, and Datsun 1600.
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