Piston Kit for Stihl FS66 FS62 FS56 Trimmer 31mm 4123030200

Piston kit for Stihl FS66, FS66 R, FS62, FS62 R and the vintage FS56 trimmer, 31mm bore, replacing Stihl part number 4123 030 2000. Stihl used the FS56 name on two different machines and only one of them is covered here. The vintage FS56 is the 4125 series at 31mm and this kit fits it. The FS56, FS56 R, FS56 C-E and FS56 RC-E sold in recent years are the 4144 series at 34mm and use piston 4144 030 2002, which is not interchangeable. Displacement will not tell the two apart, since both are quoted around 27cc, so check the bore or the series number on the machine tag. The kit contains the piston, two compression rings at 31mm by 1.3mm, the wrist pin and two circlips, which matches the Stihl parts book for this engine. A scored piston on this engine usually follows an air leak or a lean setting, so inspect the intake boot and crankshaft seals and pressure test the crankcase before fitting new parts.

• FITS STIHL FS66, FS66 R, FS62, FS62 R AND THE VINTAGE FS56 trimmers. Bore is 31mm. Replaces Stihl 4123 030 2000. If the trimmer has lost compression, will not start after sitting on old fuel, or has scoring visible through the exhaust port, the top end is the repair.
• READ THIS BEFORE ORDERING IF YOU HAVE AN FS56. Stihl used the FS56 name on two completely different machines. The vintage FS56 is the 4125 series and is 31mm, which this kit fits. The FS56, FS56 R, FS56 C-E and FS56 RC-E sold in recent years are the 4144 series and are 34mm, and this kit will NOT fit them. Their piston is 4144 030 2002. Check the series number on the machine tag.
• BORE IS THE ONLY THING THAT SETTLES IT. Do not go by displacement. Both the old 31mm engine and the current 34mm engine are quoted around 27cc, so the cc figure will fool you. Measure the bore or read the four digit series number, 4122, 4123 or 4125 for this kit, 4144 for the newer machine.
• IN THE KIT: the piston, two compression rings at 31mm by 1.3mm, the wrist pin and two circlips. Two rings is correct for this engine and matches the Stihl parts book. Kits that ship a single ring for an FS66 are short a part.
• WHY IT SCORED IN THE FIRST PLACE. A scored piston on a trimmer this size almost always follows an air leak or a lean carburetor setting rather than honest wear. Check the intake boot for cracks and the crankshaft seals for hardening, pressure test the crankcase, and fit a new cylinder base gasket before you run fuel through the new piston.