Small Engine Parts and Piston Ring Kits

Bore diameter, ring thickness and the saw they fit

A piston ring kit is sold by two measurements and a list of compatible models. A kit labeled 50 mm x 1.2 mm has rings for a 50 mm bore and a ring thickness of 1.2 mm, and the listing names the saws it suits by make and model. Match the cylinder bore of your engine, not the saw's name, and check the ring thickness, because a ring that is too thick will not seat in its groove.

Engine model numbers, not brand names

Engines of the same brand differ by model and year, so work from the model number, not the make alone. Find it on the saw or engine plate and compare it with the fit list. A new ring set is only part of a repair: measure the cylinder and piston for wear and scoring, and replace the piston or cylinder if they are damaged, since new rings in a worn bore will not seal. Two-stroke and four-stroke engines use different pistons, rings and other internal parts, which do not swap between them.

Questions about Small Engine Parts and Piston Ring Kits

How do I know which piston ring size my engine needs?

Check the cylinder bore diameter, which is the piston diameter plus a small clearance, and the ring thickness. The service manual often lists these, or you can measure the old rings and cylinder. Choose a kit that states those two values and names your engine model.

Do I need to replace the piston when I fit new rings?

Not always, but inspect it first. If the piston skirt or cylinder wall shows deep scratches, scoring or wear, new rings will not seal and the engine will lose compression. In that case replace the piston, the cylinder or both.

Does a part listed as fitting a brand come from that brand?

Not necessarily. Words such as fits or for a brand name mean the part is intended to be compatible with those models, not that the brand made it. Compare the dimensions and model list, and expect small differences from the original part.