§ 02 / Brand
PROX
ProX is what you fit when the top end's tired and the budget won't stretch to OEM. Pistons, rods, gaskets, bearings, cables, levers, wheel spacers — workshop staples held to tight tolerances. Built for the rider who pulls the engine in winter and expects it to last the season. Filter by category to find your rebuild parts.
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PROX — frequently asked questions
Common questions, straight answers. No fluff.
- Yes. Tolerances meet or beat factory spec. Drops straight into stock cases and chassis with no machining, no shimming, no fettling.
- Yes, and it is the job PROX was built for. Once a four-stroke passes the service-hour mark and head and bore tolerances start drifting, the piston kit, rings, valves, cam chain and gasket set restore compression and oil control without paying dealer counter prices. The forgings and castings sit inside the same dimensional windows as the originals, so valve clearances come back into shim range and ring end-gaps land on the number the manual asks for. Buy the kit, not the individual line items.
- Measure the bore with a dial bore gauge before you order. Pistons are graded A, B or C against the cylinder coating wear. Wrong grade, wrong piston-to-wall clearance.
- PROX runs in race engines for a reason. The pistons, rods and bearings carry the reciprocating loads of a hard-revved motor through full motos without protest, and the metallurgy copes with the heat soak that comes after the chequered flag when the rider sits on the line idling. Forged rods, cast and forged pistons depending on application, properly hardened wrist pins. The parts that come back from a national weekend looking tired are rarely the PROX ones. Workshops keep stock on the shelf because rebuilds turn around fast and the components are predictable.
- Year, model and engine generation. Manufacturers change wrist pin diameters, ring profiles and gasket shapes mid-cycle without warning. A 2018 head gasket and a 2019 head gasket from the same model can be different parts. Confirm against the VIN-matched parts diagram.
- Most listings carry the OEM cross-reference so the part can be checked against the factory schematic. Use the diagram to confirm the component you are pulling out matches the one going in. The cross-reference is a guide, not a substitute for reading the manual.