Piston kit, 40mm, for the Stihl 31.4cc 4-MIX engine. Replaces Stihl part number 4180-030-2001. Contents: piston, ring, wrist pin and circlips. The ring on its own is 4180-034-3000, 40mm by 1.2mm. Fits FS100, FS100R, FS100RX, FS110, FS110R, FS110X, FS110RX, FS111, FS111R, FS111RX, HT73, HT100, HT101, HT102, HT103, KM100, KM100R, KM110R, KM111R, FC100, FC110, FC111, FT100, HL100 and HL100K. Check the bore before ordering. Stihl built three different bores in the 4180 series and the prefix alone will not tell you which one you have: 38mm - 4180-030-2007 - FS87, FS90, FS91, KM90, HL90, HL95 40mm - 4180-030-2001 - this kit 43mm - 4180-030-2003 - FS130, FS131, KM130, KM131, HT130, HT131 None of the three interchange. Two things that matter on a 4-MIX rebuild. Valve clearance is 0.10mm, which is 0.004 inch, on both valves, checked cold, and Stihl calls for a check around every 135 running hours. And the engine has no sump, no oil pump and no oil filter - the valve train and the bottom end are lubricated entirely by the oil mixed into the fuel. Fifty to one, every tank. A 4-MIX run on straight gasoline does not just seize a piston, it wrecks the valve train, and that is how most of these arrive on the bench. Some machines in this range changed part number partway through production, so check yours against the parts diagram if the machine is a late one. Piston kit only. Cylinder, valves, gaskets, crankshaft seals and the needle bearing are not included.
- 40MM 4-MIX PISTON KIT - Piston, ring, wrist pin and circlips. Replaces Stihl part number 4180-030-2001. For the 31.4cc 4-MIX engine. Ring is 4180-034-3000, 40mm by 1.2mm, if you need one separately.
- FITS THE 40MM 4-MIX MACHINES - FS100, FS100R, FS100RX, FS110, FS110R, FS110X, FS110RX, FS111, FS111R, FS111RX, HT73, HT100, HT101, HT102, HT103, KM100, KM100R, KM110R, KM111R, FC100, FC110, FC111, FT100, HL100 and HL100K.
- THREE DIFFERENT BORES WEAR THE SAME 4180 PREFIX - 38mm is 4180-030-2007, for the FS87, FS90, FS91, KM90, HL90 and HL95. 40mm is this one. 43mm is 4180-030-2003, for the FS130, FS131, KM130, KM131, HT130 and HT131. Same series number, three pistons, no interchange. Go by the bore, not the prefix.
- SET THE VALVE LASH - A 4-MIX has a valve train, and clearance is 0.10mm - 0.004 inch - on both intake and exhaust, checked cold. Stihl calls for a check around every 135 running hours. Lash that has drifted costs power long before it costs an engine.
- NEVER RUN IT ON STRAIGHT GAS - A 4-MIX has no sump, no oil pump and no oil filter. The whole engine, valve train included, is lubricated by the oil in the fuel. Fifty to one, every tank. Running one dry destroys the valve train as well as the piston. Cylinder, valves, gaskets, crank seals and the needle bearing are not included.