Pop Up Piston Kit Husqvarna 455 Rancher 47mm 537293004

Pop-up piston kit for the Husqvarna 455 and 455 Rancher. Bore 47mm. Replaces Husqvarna 537293004, superseded from 537293002. SPECIFICATION Bore - 47mm Stroke - 32mm Displacement - 55.5cc Piston ring - 503289050 FITS. 455, 455 Rancher, 455 Rancher II, 455e Rancher II, 455 Rancher II TrioBrake. Jonsered CS2255 is the same saw. NOT THE 460. This needs saying plainly because a great many listings get it wrong. The 460 and 460 Rancher are 49mm bore, 60.3cc engines. They do not take a 47mm piston. If you have a 460 and you order from a listing that claims '455/460 47mm', you will receive a piston two millimeters too small. THE HUSQVARNA RANGE BY BORE 445 - 42mm - 45.7cc 450 - 44mm - 50.2cc 357XP - 46mm - 57cc 455 Rancher - 47mm - 55.5cc - THIS PISTON 359 - 47mm - 59cc - 34mm stroke, different piston 460 Rancher - 49mm - 60.3cc Note that the 455 and the 359 are both 47mm. They have different strokes and different compression heights, so the bore is not a fitment check on this range. Go by the part number. WHAT A POP-UP PISTON IS. The crown is raised so that it projects further into the combustion chamber at top dead centre. That reduces chamber volume and raises the compression ratio, which gives sharper throttle response and more low-end pull. Husqvarna's own piston is flat topped. MEASURE YOUR SQUISH CLEARANCE. A raised dome consumes squish clearance directly. Check it with solder through the plug hole before final assembly. Deleting the base gasket and fitting a pop-up are alternatives, not a combination - do both and the crown can contact the head.

• FITS THE HUSQVARNA 455 AND 455 RANCHER - 47mm bore, 32mm stroke, 55.5cc. Replaces Husqvarna 537293004, and the superseded form 537293002. Covers the 455 Rancher II, 455e Rancher II and the TrioBrake version. The Jonsered CS2255 is the same saw and takes the same piston.
• NOT THE 460 OR 460 RANCHER - AND THE INTERNET IS WRONG ABOUT THIS - You will find any number of listings advertising a 47mm kit for the '455 and 460'. The 460 Rancher is a 49mm engine, 60.3cc. A 47mm piston in it is two millimeters undersize. Check your model plate, not somebody else's fitment list.
• THE OTHER 47mm HUSQVARNA IS THE 359 - also 47mm, but 59cc with a 34mm stroke, so the compression height is different and nothing crosses. The 357XP nearby is 46mm. The 450 is 44mm and the 445 is 42mm. Bore alone will not identify your saw on this range - match the part number.
• RAISED DOME, NOT THE STOCK FLAT TOP - The crown projects further into the combustion chamber at top dead centre, which lifts compression and sharpens throttle response and low-end pull. Husqvarna does not make a pop-up piston; the factory part is flat topped. This is a performance variant and it is sold as one.
• MEASURE SQUISH BEFORE YOU RUN IT - A raised dome eats squish clearance directly. Check it with a length of solder through the plug hole and turn the engine over by hand before final assembly. Do not delete the base gasket as well - the two changes stack and the crown can reach the head. Raised compression also raises detonation risk, so keep the fuel fresh and the tune rich rather than lean.