OK, I have a dumb question.
If the piston on your saw is scored and you have low to no compression, is the problem the scored piston or the rings?
The rings make almost all of the compression. The issue with a scored piston is typically going to be the rings get seized and the aluminum transferred from the piston to the cylinder does not allow the rings to seal against the cylinder wall tightly. It is possible to have a lightly scored piston still function if the rings are unaffected and the amount of aluminum transferred in minimal. Reed valve saws can run with stuck rings and scored piston. It is more about running properly and long term performance. Once scoring has occurred it will only get worse until the engine stops working and the issue or cause of the damage is repaired a long with any additional damaged parts. A scored piston and cylinder is almost always a symptom of the actual problem.
Is it always necessary to replace the piston and rings - what about the cylinder, or can you hone it out?
In most instances it is better to replace the piston and the rings if both have damage. It is not always required but is the easiest way to ensure good results that will last. Do a search for information about honing, lots of information and opinions on that subject. The cylinder can often be re used if the cylinder wall, port edges and plating have not suffered severe damage.
Doesn't the compression come from the rings and if so, then why care about if the piston is scored?
A scored piston will trap carbon, etc. in the marks and tend to wear out fast and or cause additional damage to the cylinder. The piston wall is also needed to build compression, provides "bearing or "guiding" wear surface and to guide the air charge through the cylinder.
Just courious - thanks for your replies in advance.
Bill
