35 mm Cylinder & Piston Kit for STIHL FS120 2-MIX / FS120 R 2-MIX – 4134 020 1221

Description

This STIHL FS120 2-MIX cylinder kit is an aftermarket 35 mm cylinder and piston assembly for STIHL FS120 2-MIX and FS120 R 2-MIX brushcutters using OEM cylinder assembly 4134 020 1221.

The 2017 STIHL parts list identifies 4134 020 1221 as a Ø35 mm cylinder with piston and assigns it specifically to:

• STIHL FS120 2-MIX
• STIHL FS120 R 2-MIX

It is not the standard non-2-MIX FS120 cylinder.

Fits

• STIHL FS120 2-MIX
• STIHL FS120 R 2-MIX

OEM cylinder assembly reference:

• 4134 020 1221
• 4134-020-1221
• 41340201221

Cylinder diameter:

• 35 mm

OEM 4134 020 1221 Engine References

For the 4134 020 1221 version, STIHL specifies:

• Cylinder with piston – 4134 020 1221
• Piston Ø35 mm – 4134 030 2017
• Piston rings Ø35 × 1.2 mm – 4134 034 3003
• Piston pin 10 × 6.5 × 23 mm – 1139 034 1500
• Piston-pin circlips – 9463 650 1000
• Cylinder-base gasket – 4134 029 2301
• Small-end needle bearing 10 × 13 × 12.5 mm – 9512 003 2250

These references are useful when checking which top-end version is fitted to the engine. They describe the OEM engine assembly and should not be taken as a promise that every one of these separate items is supplied with this aftermarket kit.

Important 2-MIX and Revision Check

This is not the ordinary FS120 / FS120 R cylinder.

In the same STIHL parts list, standard FS120 and FS120 R machines use a different cylinder and piston configuration. The 4134 020 1221 assembly belongs specifically to the 2-MIX versions.

There is also a later factory revision. STIHL’s 2019 parts list specifies 4134 020 1222, still Ø35 mm, for FS120 2-MIX and FS120 R 2-MIX, together with revised piston 4134 030 2023 and rings 4149 034 3005.

Therefore this listing is specifically for the 4134 020 1221 version. When repairing a later machine, identify the installed top-end version before mixing individual piston, ring and cylinder references from the 1221 and 1222 configurations.

Before Installing a New Cylinder

If the original piston is badly scored or seized, find the cause before fitting the new cylinder. Check:

• Carburetor mixture and fuel supply
• Fuel filter and fuel lines
• Intake-system air leaks
• Crankshaft seals
• Correct two-stroke fuel mixture
• Cooling passages and general overheating

A lean-running engine can damage a new piston and cylinder very quickly.

During assembly, inspect the connecting rod and small-end needle bearing. Lubricate the piston, rings and cylinder with clean two-stroke oil, align the piston rings with their locating pins and install the piston in the correct orientation.

Use the correct cylinder-base gasket and tighten the cylinder fasteners according to STIHL service specifications.