Chainsaw Rebuilds Piston Wear on saws?

[oceancruze1]

I am new to rebuiding chainsaws but have rebuilt automotive race engines. Do pistons actually wear in chainsaws rather than just rings like in automotive engines? Do you use a micrometer to determine how much wear there is? What about cylinders, what can you do to get the prepared for a rebuild. If there is no scoring do you throw it back together, scuff up the walls to get the rings to seat? What do you do it there is some scoring albeit maybe slight, try and clean it up with??? What should the compression be on most saws specifically a Stihl to determine if it needs a rebuild in the first place

 

[timberwolf]

Pistons do wear, the skirts wear down and then the piston rattles around and starts tilting in the bore and unseating rings as well as doing a poor job of sealing ports. Nikasil bores tend to wear very little. But if they get scored up there is not much you can do. Only very light scratches can be honed out, plating is only a couple thou thick. Honeing is a last resort IMHO, try localized clean up with fine sand paper first. Aluminium transfer to bore from a scuffed piston is another matter and it can be cleaned with muriatic acid.

Good compression should be in the 150-160 plus PSI range, below 140 psi is suffering, below 120 is toast.