The Extrema is the bike the later ones are still compared with. It is a small Grand Prix replica in the literal sense: a single-cylinder Rotax two-stroke in a silver or polished aluminium frame, with a rectangular headlight and a mechanical rev counter. The factory code on the frame is GS. The Sport Pro uses LA. Neither of those numbers starts with ZD4. That prefix arrives with the MP.

How to recognise one

Look at the lamp first. This generation has a rectangular headlight. The next body, which keeps a similar fairing, switches to a round lamp with a small lip under it. The clocks are the other quick tell: an analogue temperature gauge and a cable-driven tacho. The tacho drive is not a curiosity. The brief says the shaft is fragile and no longer available, so a dead cable on one of these is a parts problem, not a five-minute job.

The frame colour is a year clue, not a full identification. The brief says frames were painted silver until about 1995 and polished after that, and it separately lists a 1994 polished-frame Telaio Lucido. A polished frame on its own does not prove the edition. Read the frame number.

The engine you have to get right

This generation is a Rotax 123. The casting to look for is “Rotax 123” at the left rear, by the engine number. The carburettor is a Dell’Orto VHSB 34 and the ignition is SEM. Cylinders, gearboxes, clutches, gaskets and ignitions do not swap with the Rotax 122 that Italy started fitting from 1995. If a seller describes an early bike as “just the usual 122”, stop and read the casting.

Hartrusion, via the brief, gives the homologated power as 23 kW (31.3 PS) and says there was no factory-restricted version. UK bikes of the next generation were often sold at 15 bhp. Do not copy that assumption back onto a GS. To verify any restrictor someone has added later: the brief does not describe a factory blanking plate for this generation.

What usually fails

The starter freewheel and the ring gear on the flywheel wear. The SEM stator is already scarce. The mechanical tacho drive is the part the brief says you cannot buy new. Plan a 123 rebuild around what is still made — PJME is the UK specialist named in the brief — and treat missing 123-only parts as a reason to walk away from a cheap project, not as a weekend surprise.

Service life of the top end is the one mileage figure the brief records from MCN, and it is for the two-strokes as a group: rings around every 5,500 miles, piston and barrel around every 10,000 miles. Clearances and torque are not in the brief.

Special editions

Reggiani (1992, with a 1995 decal set also recorded), Chesterfield (1994), Telaio Lucido (1994) and the Sport Pro sit on this generation. A replica is the sticker kit. The mechanical bike is the GS or LA of that year. The Chesterfield name comes back on the bee-tail from 1999 to 2005. It is not listed as a 1998 scheme.