The Namura NA-50001-4K Top End Kit is designed for select 1990–1993 Polaris Trail Boss 350L 2x4 and 4x4 models. This 80.95 mm (+1.00 mm) oversized piston kit features an 11:1 compression ratio and provides the core components needed for a reliable top-end rebuild. The kit includes a piston, piston rings, wrist pin, wrist-pin clips, top-end bearing, and gasket kit for convenient installation.
Namura uses a hypereutectic casting process to increase silicon content, helping reduce expansion, improve wear resistance, and withstand higher cylinder temperatures. The piston skirts feature a rolled-on MOS2 coating made from Teflon and molybdenum. This application creates a bond reported to be significantly stronger than spray-on coatings while helping transfer heat, reduce friction, and minimize the risk of cold seizures.
Additional piston features include machined smooth heads and anodized domes. The smooth head surface helps reflect combustion heat and reduce carbon buildup, while the anodized dome improves heat resistance and durability. Together, these design elements help protect the piston and support consistent performance during demanding riding conditions. The Namura NA-50001-4K is intended for standard top-end service when cylinder preparation and final clearances are completed according to manufacturer specifications.
Fitment: Fits 1990, 1991, 1992, and 1993 Polaris Trail Boss 350L 2x4 models, plus 1990, 1991, 1992, and 1993 Polaris Trail Boss 350L 4x4 models. Verify the existing cylinder, required oversize, compression ratio, and service specifications before installation.
Features:
- Complete top-end kit includes piston, rings, wrist pin, wrist-pin clips, top-end bearing, and gasket kit
- 80.95 mm (+1.00 mm) oversized piston supports cylinder rebuilding and top-end replacement
- 11:1 compression ratio is designed for compatible Polaris Trail Boss 350L applications
- MOS2 Teflon/molybdenum-coated skirts help reduce friction, improve heat transfer, and minimize cold-seizure risk
- Machined smooth head helps reflect combustion heat and reduce carbon buildup
- Anodized dome improves heat resistance and piston durability
- Hypereutectic casting process provides reduced expansion, improved wear resistance, and increased high-temperature capability
- Fitment includes 1990–1993 Polaris Trail Boss 350L 2x4 and 4x4 models
- Brand: Namura
- Manufacturer part number: NA-50001-4K
- Vendor part number: 186-50014
Fitment:
1990 Polaris Trail Boss 350L 2X4
1990 Polaris Trail Boss 350L 4X4
1991 Polaris Trail Boss 350L 2X4
1991 Polaris Trail Boss 350L 4X4
1992 Polaris Trail Boss 350L 2X4
1992 Polaris Trail Boss 350L 4X4
1993 Polaris Trail Boss 350L 2X4
1993 Polaris Trail Boss 350L 4X4