Genuine OS factory piston for the FS-56α (FS-56A) four-stroke glow engine. The piston is the wearing heart of the compression system, and a fresh one is the fix for an engine that's down on pinch, hard to start, or showing blow-by after a long service life.

Note: the piston ring is not included — order ring 44603400 alongside, as a new ring should always be fitted with a new piston.

Piston and cylinder liner wear together as a matched pair, so inspect the liner bore while the engine is stripped — scoring, wear ridges, or corrosion mean the liner (part 44603100, available separately) should be replaced at the same time. Fitting a new piston into a worn bore gives away most of the improvement. Reassemble with a new head gasket, as the original will have crushed in service, and check the piston pin and its retainers for wear while they're out.

After the rebuild, run the engine in as if new: several tanks rich to bed the fresh surfaces before leaning out. Expect starting and compression to feel factory-tight again.

Specifications

Brand: OS Engines (Japan)
Part number: 44603200
Type: Piston (ring 44603400 not included)
Suits: OS FS-56α (FS-56A) four-stroke