Husqvarna 266 266XP 52mm Big Bore Cylinder & Piston Kit

Lil Red Barn 52mm Big Bore Cylinder and Piston Kit for Husqvarna 266, 266XP and 266SE The 52mm top end, with the intake adapter block included. A deliberate bore upgrade for a 50mm saw that already needs a top end, not a stock replacement part. WHAT IS INCLUDED Closed-port 52mm cylinder 52mm piston with rings, piston pin and circlips Intake adapter block WHY THE ADAPTER BLOCK MATTERS The 266 and the 52mm cylinder use different intake arrangements. The 266's own intake block has separate bolts and will not serve on this cylinder, so the adapter is not an accessory, it is part of the conversion. It is in the box. WHAT THE JOB MAY STILL WANT Carburetor screws in the 272 pattern, because the two carburetors have different bolt orientations; possibly a different impulse line and muffler. The 266XP top cover fits, though it is tight. STOCK OR UPGRADE A standard 266, 266XP, 266SE or Jonsered 630 is 50mm, and the stock assembly is Husqvarna 503517502. Caliper the old bore before ordering: 50mm is stock, 52mm means the saw has already been converted, and 48mm is a different saw entirely. BEFORE ASSEMBLY Measure squish with solder through the plug hole at four points around the piston, turning the engine through top dead centre by hand. Check ring end gap in this cylinder rather than the old one. Fit new crankshaft seals while the engine is open.

• 52MM TOP END WITH THE INTAKE ADAPTER BLOCK INCLUDED - A closed-port 52mm cylinder and piston for the 266, 266XP and 266SE, and for the Jonsered 630. The adapter block is in the box, and it has to be: the 266's own intake block will not serve on this cylinder because the 266 uses a different design with separate bolts. Several kits sold at this size leave you to find one.
• THIS IS AN UPGRADE, NOT A STOCK PART - A standard 266, 266XP, 266SE or Jonsered 630 is 50mm. This is the 52mm top end, which is the 272XP size. The stock 50mm assembly is Husqvarna 503517502, and that is the part to order if you want the saw back to original. Caliper the old bore before you decide: 50mm is stock, 52mm means someone has already been here.
• WHAT IS IN THE BOX, AND WHAT THE JOB MAY STILL WANT - Cylinder, piston, rings, piston pin, circlips and the intake adapter block. Not included and worth having to hand: the carburetor screws in the 272 pattern, because the two carburetors have different bolt orientations, and possibly a different impulse line and muffler. The 266XP top cover does fit, though it is tight.
• WHEN IT IS WORTH DOING - Straight from a builder who has done both: the gain is noticeable, but it is not worth pulling a 266 apart for if the saw is running fine. If the engine already needs a top end, it makes a good project and the cost over a stock rebuild is small. That is the honest version, and it is the reason this page tells you the stock part number as well.
• MEASURE SQUISH BEFORE YOU TRUST IT - Crush a length of solder through the plug hole at four points around the piston, turn the engine slowly through top dead centre by hand, then measure. Cylinders of the same part number vary. Check ring end gap in this bore rather than the old one, fit new crankshaft seals while the engine is open, and use a ring compressor on assembly.