Question 1

Apex Seal Wear

Accepted Answer

Gradual 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.

Question 2

Oil Metering Pump Failure

Accepted Answer

The 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.

Question 3

Cooling System Inadequacy

Accepted Answer

The 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.

Question 4

Exhaust Port Gasket Leaks

Accepted Answer

Exhaust 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.

Question 5

Carburettor Deterioration

Accepted Answer

Poor 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.

Question 6

Fuel Tank Corrosion

Accepted Answer

Restricted 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.

Question 7

Floor Pan Corrosion

Accepted Answer

The floor pans perforate, weakening the car's structure and allowing moisture and exhaust fumes into the cabin. Moisture trapped under carpets, combined with road spray from underneath. The R100's floor has minimal corrosion protection by modern standards. Australian humidity and occasional flooding accelerate the process. Cut out corroded sections and weld in new steel. This is not a patch-and-fill job, the floor pans are structural. A good panel beater or fabricator can manufacture repair sections. Cost: $1,000-3,000 per area, depending on severity.

Question 8

Sill and Rocker Panel Rot

Accepted Answer

The box-section sills that run along each side of the car corrode from the inside, eventually perforating and losing structural rigidity. Water enters through drain holes (or blocked drain holes) and sits inside the sill. Corrosion progresses invisibly until it breaks through the outer skin. Cut out corroded sections and fabricate new sill panels. This is a specialist job requiring welding and panel-fitting skills. Cost: $1,500-3,000 per side for significant corrosion.

Question 9

Rear Wheel Arch Corrosion

Accepted Answer

Rust develops in the inner and outer wheel arches, spreading from the inside. Road spray, mud, and moisture accumulate in the arches. The R100's arch lips trap debris. Cut and patch. Outer arches are visible, repairs need to be cosmetically acceptable. Inner arches can be patched more roughly. Cost: $500-1,500 per arch.

Question 10

Wiring Harness Degradation

Accepted Answer

Intermittent electrical faults, lights flickering, gauges dropping out, fuses blowing, or worse, no faults at all until a short circuit causes a fire. The original wiring harness uses rubber-insulated wire that becomes brittle and cracks after 50 years. Exposed copper causes short circuits. Previous owners' repairs often involve inappropriate wire, poorly crimped connectors, and electrical tape. Inspect the entire harness. Minor damage can be repaired in situ. Severe degradation requires a rewire, either a custom harness or a universal kit adapted to the R100. Cost: $500-2,000 depending on approach.

Question 11

Charging System Failure

Accepted Answer

Battery not charging, dim lights, engine dying while running. The original alternator (or generator, on very early cars) wears out. Brushes wear, diodes fail, regulators degrade. The low-output original alternator may also be inadequate if accessories have been added. Rebuild or replace the alternator. A higher-output alternator from a later Mazda model may be adaptable. Cost: $100-300 for a rebuilt unit.

Question 12

Leaf Spring Sag and Fatigue

Accepted Answer

The rear of the car sits low, the ride becomes bouncy or harsh, and handling deteriorates. Cracked leaves may be visible on inspection. The R100's rear leaf springs lose their temper after 50 years of use. The original springs were designed for a car weighing approximately 850 kg, if the car has been loaded heavily or used on rough roads, the springs fatigue faster. Have new springs manufactured by a spring shop to original specifications. Alternatively, upgrade to a coil-over rear conversion if the car is being built for performance rather than originality. Cost: $300-600 for new leaf springs; $1,000-2,000 for a coil-over conversion.

Question 13

Universal Joint Wear

Accepted Answer

Vibration through the driveline, clunking during gear changes or under load. The universal joints in the propshaft wear with age and use. Heat from the nearby exhaust accelerates grease deterioration. Replace universal joints. These are relatively standard items. Cost: $50-100 per joint.

R100 (Familia Rotary)

R100 (Familia Rotary) known problems