A 54mm pop-up piston kit for the Stihl 066 and MS660. It fits where standard piston 1122-030-2005 does. The kit has the raised-dome piston, ring, wrist pin and circlips. The raised dome reduces combustion chamber volume, which raises compression, tightens squish and helps low-speed torque and starting; it is not a guaranteed gain in top-end power, and for a straight repair the standard piston is the right part. Check piston-to-head clearance with a solder test and choose base gasket thickness from what you measure. Set the high-speed mixture slightly rich and take the first tank gently.
- POP-UP PISTON KIT - A raised-dome piston with ring, wrist pin and circlips.
- FITS STIHL 066 AND MS660 - The 54mm saws. It fits where standard piston 1122-030-2005 does.
- WHAT A POP-UP DOES - The dome reduces combustion chamber volume, which raises compression, tightens squish and helps low-speed torque and starting. It is not a guaranteed gain in top-end power; for a straight repair the standard piston is the right part.
- MEASURE SQUISH ON ASSEMBLY - Cylinders vary, so check piston-to-head clearance with a solder test through the plug hole and choose base gasket thickness from what you measure. Too tight and the dome contacts the head.
- SET IT UP RIGHT - Higher compression runs hotter: set the high-speed mixture slightly rich, use fresh high-octane fuel and fresh oil, and take the first tank gently.